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Guideline for the Prevention and Control of Norovirus Gastroenteritis Outbreaks in Healthcare Settings, 2011

Evidence Table Q1 - Environmental Characteristics

Author, Yr (Ref) Study Design Quality Study Objective Population and Setting N Results Comments Ref ID_Data extracted by
MMWR; 2008 79 Prospective controlled study. 1, 3, 4 To investigate an outbreak at an elementary school. Students and staff at an elementary school in Washington DC in February 2007.
Students – median age 8 years (range 3-12 years); 55% female. Staff – median age 41 years (range 13-66 years);
 
92% female. 266 – 207 students and 59 staff.
Symptomatic norovirus infection
Bivariate analysis: All results RR (95% CI); p value
Being a student – 0.94 (0.66-1.34); 0.76
Being female – 1.13 (0.82-1.56); 0.52
Having an ill contact – 1.76 (1.16-2.67); 0.01
Classroom J (first) – 1.94 (1.34-2.80); 0.02
Library use: 0.94 (0.58-1.52); 0.87
Library computer use: 1.08 (0.41-2.84); 1.00
 
Interventions implemented
District of Columbia Department of Health recommended
-more thorough handwashing
- cleaning all shared environmental surfaces with a diluted (1:50 concentration) household bleach
-cleaning computer equipment (i.e., mice and keyboards)
-excluding ill persons from school for at least 72 hours after resolution of illness
A case of gastrointestinal illness was defined as illness in a student or staff member with nausea, vomiting, or diarrhea, who was at the school February 2-18, 2007.
 
Power and sample size not reported.
017_IL
MMWR, 2007 80 Prospective controlled study 1, 2, 3, 4 To investigate source of norovirus gastroenteritis outbreak at a family reunion. Family reunion in Grant county, West Virginia, October 2006.
 
39 included in cohort study: 19 are cases and 20 are controls.
Risk factor – unadjusted RR (95% CI); p value
Food consumed
Scalloped potatoes – RR 2.80 (1.14-6.86); 0.01
Ham – RR 2.19 (0.63-7.60); 0.24
Chicken – RR 2.16 (0.97-4.81); 0.04
Chocolate cheese ball – RR 2.14 (1.26-3.65); 0.04 – only eaten by 7 individuals
Onion dip – RR 1.65 (0.88-3.07): 0.23
Meatballs – RR 1.54 (0.79-3.03); 0.21
Green beans – RR 1.44 (0.76-2.73); 0.27
Cream cheese roll-ups – RR 1.43 (0.77-2.65); 0.29
Cheese ball – RR 1.43 (0.72-2.83); 0.66
Chip dip – RR 1.33 (0.69-2.54); 0.42
Buterscotch cake – RR 1.24 (0.61-2.52); 0.71
Cole slaw – RR 1.17 (0.60-2.30); 0.65
Deviled eggs – RR 1.11 (0.59-2.10); 0.75
Pasta salad – RR 1.04 (0.57-1.89); 0.90
Broccoli salad – RR 1.04 (0.52-2.07); 0.92
Chocolate cake – RR 1.03 (0.36-2.94); 1.00
Pinch-me cake – RR 1.03 (0.36-2.92); 1.00 Sugar cookies – RR 1.00 (0.42-2.39); 1.00
Coffee – RR 1.00 (0.46-2.19); 1.00
Soda – RR 0.90 (0.47-1.70); 0.74
Spicy rice casserole – RR 0.89 (0.39-1.77); 1.00
Parsley potatoes – RR 0.83 (0.39-1.77); 0.63
Potato casserole – RR 0.74 (0.37-1.50); 0.40
Raw vegetables – RR 0.74 (0.34-1.62); 0.43
Pecan cake – RR 0.70 (0.27-1.83); 0.69
Coffee creamer – RR 0.69 (0.13-3.54); 1.00
Mandarin orange cake – RR 0.63 (0.19-2.04); 0.66
Macaroni salad – RR 0.53 (0.22-1.28); 0.11
Turkey – RR 0.40 (0.0-2.39); 0.35
Baked beans – RR 0.38 (0.11-1.34); 0.12
Fruit cocktail – N/A
Other risk factors
Contact with ill person – RR 2.27 (1.01-5.07); 0.03
At home A prereunion gathering – RR 1.57 (0.87-2.81); 0.24
At home B prereunion gathering – RR 0.92 (0.46-1.81); 0.80
12/13 stool specimens tested positive for norovirus genogroup II by RT-PCR.
 
Power and sample size not reported.
3864_IL
Costas L, 2007 81 Prospective controlled study
 
1, 2, 3, 4, 6, 7
To investigate a norovirus outbreak among hospital staff. Healthcare workers at a hospital in Barcelona, Spain.
 
31/38 cases available for interview.
31 unmatched healthcare workers selected as controls
Risk factor – OR (95% CI); p value
Rice salad with cocktail sauce – OR 4.11 (1.14-14.72); 0.03
Waterborne source – OR 0.675 (0.237-1.924)
September 12th (when rice salad with cocktail sauce served) – OR 3.37; p=0.07
Norovirus identified from stool samples – testing used not defined.
 
Power and sample size not reported.
IL_6577
Lopman, BA; 2005 82 Prospective controlled study
 
1, 2, 3, 4, 6, 7
To evaluate institutional factors related to gastroenteritis outbreaks in hospitals. Outbreaks occurring in 3 hospital administrations (NHS trusts) in England. These trusts include 4 major acute hospitals and 11 community hospitals, which comprise 171 inpatient functional care units. Outbreak rates (study duration 52 weeks)
Overall
227 outbreaks in 113 units – 1.33 outbreaks/unit-year
 
Hospital Type
Acute center vs. community –
1.5 (1.3-1.8) vs. 0.9 ( 0.7-1.2); 0.0002
 
All results are rate (95% CI)
Unit specialty; p<0.0001
Other types – 1.0 (0.8-1.3)
General medical – 2.5 (1.9-3.2)
Geriatric – 1.9 (1.4-2.6)
Surgical – 1.2 (0.8-1.8)
Orthopaedics – 1.9 (1.2-2.9) Mental health – 0.7 (0.3-1.5)
 
No previous outbreak vs. previous outbreak – 0.9 (0.8-1.1) vs. 2.4 (2.02.9); p<0.0001
 
Month following outbreak vs. rest of follow-up period – 3.3 (2.4-4.6) vs. 1.3 (1.1-1.5); p<0.0001
 
Outbreak risk factors
(study duration 52 weeks)
All results are HR (95% CI); p value
Univariate analysis
Number of beds in unit (per additional 10 beds) – 1.50 (1.25-1.81); <0.0001
Average length of stay (per additional week) – 0.96 (0.92-1.00); 0.04
Unit in acute centre vs. community hospital – 1.80 (1.31-2.49); 0.0002
Previous outbreak – 2.00 (1.50-2.67); 0.0001
Month following outbreak vs. other time – 2.05 (1.41-2.98); <0.0001
General medicine vs. geriatric vs. orthopaedics – 2.48 (1.76-3.49) vs. 1.94 (1.32-2.85) vs.1.90 (95% CI 1.17-3.08); <0.0001
 
Multivariable analysis
Number of beds in unit (per additional 10 beds) – 1.22 (0.96-1.55); 0.10
Average length of stay (per additional week) – 0.89 (0.80-0.99); 0.041
Previous outbreak – 0.88 (0.62-1.25); 0.47
Hospital ward type – p=0.006
General medicine – 1.71 (1.11-2.63)
Geriatric – 2.55 (1.52-4.25)
Surgical – 0.79 (0.48-1.29)
Orthopaedics – 1.43 (0.82-2.49)
Mental Health – 2.30 (0.36-14.9)
Power and sample size not done.
 
Noroviruses were detected in 65% of all outbreaks where specimens were available.
511_IL
Evans, M; 2002 83 Prospective controlled study
 
1, 3, 4
To describe an outbreak of norovirus gastroenteritis following vomiting by an attendee at a concert Primary school children attending a concert at a metropolitan concert hall. Demographic characteristics not provided.
 
1229 children from 15 primary schools
Description of outbreak
Following the vomiting, cleaning was done with an ordinary vacuum cleaner the following day. No hypochlorite based product was used. The index case was seated in tier 13.
 
Auditorium seating as a risk factor for symptomatic norovirus infection (follow-up not clearly reported)
Children seated in tiers 9-13 vs. children seated elsewhere – 199/387 vs. 58/797; RR(95% CI) = 7.1(5.4-9.2)
A case was defined as a person who had attended the concert hall and had developed vomiting and/or diarrhea within 24-72 hrs of the visit.
 
NLV was confirmed in fecal samples using RT-PCR Power and sample size not reported
897_RA
Lachlan, M; 2002 84 Prospective controlled study
 
1, 3, 4
To describe an outbreak of norovirus gastroenteritis and lessons learned. Persons with a connection to a hotel linked to the outbreak or ill contacts of people who were unwell and had a connection with the hotel.
 
112 potentially exposed, 79 cases

Symptomatic norovirus infection - Food specific attack rates
Beef sandwich – 1.35(1.08-1.67)
Cheese sandwich – 1.33(1.06-1.67)
Egg sandwich – 1.49(1.18-1.88)
Ham sandwich – 1.39(1.14-1.69)
Lamb sandwich – 1.46(1.28-1.66)
Tuna sandwich – 1.27(1.02-1.60)
Sausage sandwich – 1.01(0.77-1.32)
Soup – 1.28(1.00-1.64), P<0.05
Parsley garnish – 0.71(0.18-2.83)
Tomato garnish – 1.15(0.82-1.61)
Hot chocolate – 1.45(1.28-1.65)
Tea – 1.04(0.81-1.33)
Coffee – 1.36(1.10-1.67)
Ice – 1.25(1.00-1.57)
Other drinks – 1.52(1.12-2.05)

After applying a critical P value (<0.003) with Bonferroni correction, only egg sandwich and drinks from the bar (other drinks) were found to be statistically significant.

 

Lessons from the outbreak

  1. Outbreak control team meetings that are formally minuted with action points being highlighted on a flipchart
  2. Good liaison with laboratory services to agree on clear pathways for the delivery and analysis of samples that became available during normal working hours or were processed over the weekend.
  3. Rapid virological confirmation to reassure the public that appropriate control measures were in place and handle the media interest.
  4. Joint visit to the outbreak premises by protective services and public health representatives to facilitate clear and open communication between all parties and secure a voluntary agreement from the hotel owner to cease all food preparation.
  5. Food handlers should remain off work from onset of illness until 48 hours after diarrhea and vomiting have ceased
  6. All those involved in carrying out interviews and analyzing data working from one site and through one computer network to improve the efficiency of working through contact lists, allowing rapid assessment of the epidemic curve and symptom pattern and the results of RR calculations of the foodstuffs.
A case was defined as someone with symptoms of diarrhea, vomiting or abdominal pain or any combination of these more than once in 24 hours and a connection with the hotel where the outbreak started.
 
Norovirus was confirmed by EM
942_RA
Love, S 2002 84 Prospective controlled study
 
1, 3, 4
To describe an outbreak of gastroenteritis and procedures implemented to control it. Guests and employees of a Virginia hotel. There were 3 groups:
Group A: Attendees of a business conference (n=110); median age of cases (n=34) 52 years; 59% cases female Group
B: Physicians and their families (n=95); median age of cases (n=11) 31 years; 73% cases female
Group C: Retired persons (n=310); median age of cases (n=15) 71 years; 60% cases female
 
60 cases

Risk factors for symptomatic norovirus infection (follow-up unclear)
Attending reception: RR(95% CI) – 2.1(1.1-4.0)
Eating coleslaw at picnic: RR(95% CI) – 3.6(1.0-13.6)

Interventions

Infection control measures instituted:

  1. Employees who were ill in the past two weeks or had an ill child in diapers were excluded from work for 1 day. Employees who were currently ill with vomiting or diarrhea were told not to work for 1 day after resolution of symptoms
  2. All employees were instructed about hygiene and hand washing 5 days after initial cases
  3. The facility was closed for 8 h to permit thorough cleaning of all food service areas and guest rooms. New guests were not accepted until all guestrooms, bathrooms, and common rooms were thoroughly cleaned 7 days after initial cases
  4. All cold food requiring hand-preparation was excluded from the menu. No open bowls of food such as chips or popcorn were served 7 days after initial cases

Response to intervention (at two week follow-up)
The hotel reported no further ill guests or employees

A case was defined as vomiting or diarrhea in a hotel attendee or staff.
 
Norovirus confirmed by RTPCR
 
Power and sample size not reported.
915_IL
Anderson, AD; 2001 86 Prospective controlled study
 
1, 3, 4
To identify the source of a gastroenteritis outbreak at a car dealership. Multistate investigation involving catered meals given to car dealerships spanning 13 states. Median age 37 years (range 389 years).
 
753 banquet attendees.
333 met case definition.
Symptomatic norovirus infection
Univariate analysis
All results are RR (95% CI)
Any salad – 3.8 (2.5-5.6)
Rotini pasta salad – 3.0 (2.4-3.7)
Potato salad –1.6 (1.3-1.9)
Bow-tie pasta salad –1.5 (1.3-1.8)
Vegetable salad – 1.7 (1.4-1.9)
Condiments – 1.4 (1.2-1.7)
Dips – 1.3 (1.1-1.5)
Cheeses – 1.3 (1.1-1.5)
Snacks –1.0 (0.8-1.1)
Meats – 1.1 (0.7-2.0)
Desserts – 1.2 (1.0-1.4)
Breads – 1.4 (1.1-1.9)
Case was a person who attended a "banquet dinner" at one of the dealerships and developed vomiting or diarrhea (≤3 loose stools within 24 hours).
 
2/15 caterers had elevated norovirus immunoglobulins.
 
16 specimens that were sequenced showed a common outbreak strain.
 
Power and sample size not reported.
1003_IL
Cunney RJ, 2000 87 Prospective controlled study
 
1, 2, 3, 4
To investigate a hospital NLV outbreak. Hospital outbreak
 
N= 95 persons: 47 patients and 48 staff.
Infection control practices
-Affected patients were cohorted
-Admissions to and transfers from the geriatric ward were stopped
-70% alcohol hand rub supplemented routine hand washing
-Affected staff sent home until 48 hours after symptoms subsided
-Decontamination procedures changed from standard phenolic solution to 2% hypochlorite solution
 
Food source
Drinking water from the hospital water supply: 16 symptomatic and 6 nonsymptomatic (p=0.1)
12 (13%) containing SRSV were solid phase immune electron microscopy (SPIEM) positive for NLV
 
25 (27%) sampes contained small round featureless virus (SRFV) identified by direct EM and were negative on SPIEM
 
Power and sample size not reported.
1197_IL
Marks, P; 2000 88 Prospective controlled study
 
1, 3, 4
To describe an outbreak of gastroenteritis following a meal in a hotel during which one of the diners vomited Diners attending an evening dinner at a large hotel in the UK. Demographic characteristics not reported
 
126; 52 cases
Symptoms (% of ill subjects reporting symptoms)
Nausea – 58
Diarrhea and vomiting – 42
Vomiting without diarrhea – 21
Diarrhea without vomiting – 21
Abdominal pain – 40 Fever – 38
 
Time of onset of symptoms
83% of those who became ill did so between 13 and 48 hours after the meal and 59% between 25 and 48 hours. Of the 14 people who reported precise times for the onset of their illness, the mean time from exposure to onset of symptoms was 33 hours and the median 35 hours.
 
Symptomatic norovirus infection - Attack rate in % (at each of the tables)
The lady who vomited was seated at table 2
Table 1 – 71
Table 2 – 91
Table 3 – 56
Table 4 – 50
Table 5 – 40
Table 6 – 25
 
There was a signifiant relationship between distance from the vomiter and the risk of becoming ill (P<0.01) with no significant deviation from that trend (P=0.68)
NLV was confirmed using EM and RT-PCR 83 of 126 guests (66%) returned completed questionnaires
 
Power and sample size not reported
1122_RA
Lo SV, 1994 89 Prospective controlled study
 
1, 2, 3, 4
To investigate a SRSV gastroenteritis outbeak in 4 hospitals served by one central kitchen 4 hospitals - 1 acute district general hospital and 3 smaller peripheral hospitals with long-stay and rehabilitation patients
 
81 patients and 114 staff in 4 hospitals
 
Buffet lunch cohort study: N=41 completed quesionnaire
 
Patient case-control study: N= 23/24 cases and 35/36 controls completed questionnaires.
 
Staff case-control study: N= 22/27 cases and 49/54 controls completed questionnaire.
Buffet lunch study
Food - RR (95% CI)

Ham and tomato – RR 1.0 (0.6-1.7)
Cheese and pickle – RR 0.8 (0.4-1.9)
Turkey salad – RR 2.4 (1.4-4.1)
Tuna – RR 1.2 (0.7-2.0)
Sausage roll – RR 1.1 (0.6-1.8)
Cheese and pineapple – RR 1.0 (0.6-1.8)
Sausage mushroom – RR 1.6 (0.-2.9)
Fresh fruit – RR 0.8 (0.3-2.3)
Meringue – RR 0.9 (0.5-1.4)
Orange juice – 1.0 (0.48-2.0)
Wine – 1.0 (0.51-2.1)
 
Patient case-control study
Risk factor
Food - OR (95% CI)
March 7th
Beel cobble – OR 0 (0-1.7)
Beef crumble – OR 1.6 (0-11.5)
Mince – OR 0.7 (0.1-3.9)
Sausage and onion – OR 0.3 (0.1-1.3)
Cheese pie – OR 0.2 (0-1.6)
Lamb salad – OR 0.4 (0.05-2.4)
Tuna salad – OR 6.6 (1.0-71.6); p<0.05
Any salad – OR 1.8 (0.5-6.8)
Corn beef sandwich – OR 1.6 (0.1-23)
Any sandwich OR 4.6 (0.6-39)
 
March 8th
Cod – OR 1 (0.3-3.5)
Chicken curry – OR 0.8 (0.2-2.8)
Flaked fish – OR 0.7 (0.01-15)
Lamb casserole – OR 0.9 (0.2-3.9)
Mushroom pizza – OR 0.3 (0.01-3.9)
Savoury lamb – OR 1 (0.1-9.7)
Beef salad – OR 3.2 (0.2-97)
Chicken salad – OR 2.5 (0.3-31)
Any salad – OR 4.7 (0.9-30); p <0.05
Salmon sandwich – OR 0.2 (0-2.2)
Any sandwich – OR 0.4 (0.04-2.3)
 
March 9th
Pork casserole - OR 1.5 (0.4-5.7)
Chicken pie – OR 0.3 (0.1-1.5)
Minced chicken – OR 0.2 (0-1.6)
Cawl – OR 1.6 (0.2-13)
Fishcake – OR 0.5 (0.1-2.5)
Egg salad – OR 0.3 (0-3.9)
Cheese salad – OR 2.2 (0.2-4.8)
Any salad – OR 1.1 (0.2-4.8)
Ham sandwich – OR 0.5 (0.01-6.7)
Any sandwich – OR 1 (0.1-9.7)
 
Staff case-control study
No statistically significant associations found.
 
1 food handler who prepared the salad had a child who was ill 2 days prior and the food handler became ill the day following food preparation.
 
Infection control practices
Closure of the central kitchen
Disposal of all remaining food
Discontinuing all hospital admissions and ward transfers
Daily ward cleaning with 2% hypochlorite Emphasis on hand washing
A cohort study of staff who attended a retirement buffet lunch, a patient case-control study based at the district general hospital, and a nursing staff case-control study at the district general hospital were performed.
 
Fecal samples underwent bacteriological examination, routine EM, and immuno-EM.
 
Power and sample size not reported.
1540_IL
Patterson T, 1993 90 Prospective controlled study
 
1, 2, 3, 4, 6, 7
To investigate an SRSV gastroenteritis outbreak at a conference. Outbreak at an international AIDS conference. April 23, 1990.
 
N=226/283 (80%) delegates replied to the questionnaire.
Risk factor – Unadjusted RR (95% CI); p value – the foods prepared by potential source (foodhandler) italicized
Wednesday, April 18, 1990
Canapes – RR 1.21 (0.80-1.84); 0.44
Celery – RR 1.16 (0.76-1.79); 0.59
Sausage – RR 1.2 (1.01-2.30); 0.07
 
Thursday, April 19, 1990 buffet
Chicken drumsticks – RR 1.66 (1.08-2.55); 0.03
Green salad – RR 1.42 (0.87-2.31); 0.20
Tomato and chive salad – RR 0.79 (0.51-1.23); 0.36
Ham – RR 2.18 (1.38-3.44); <0.001
Vegetable pie – RR 0.76 (0.46-1.25); 0.34
Coleslaw – RR 0.84 (0.52-1.37); 0.59
Coleslaw and rice – RR 1.27 (0.80-2.02); 0.38
 
Thursday, April 19, 1990 civic reception
Melon – RR 1.19 (0.78-1.82); 0.51
Sole – RR 1.12 (0.73-1.70); 0.70
Lamb – RR 1.23 (0.80-1.89); 0.42
Vegetables – RR 1.31 (0.85-2.01); 0.28
Chocolate roulade – RR 0.97 (0.64-1.48) 0.98
Cheese – RR 1.04 (0.67-1.63)
 
Friday, April 20, 1990 buffet
Coronation chicken – RR 3.51 (2.23-5.52); <0.0001
Green salad – RR 1.78 (1.12-2.84); 0.018
Vegetable quiche – RR 1.07 (0.70-1.63); 0.88
Potato salad – RR 1.45 (0.95-2.21); 0.11
Curried rice – RR 1.43 (0.93-2.19); 0.13
Tomato and chive salad – RR 1.02 (0.73-1.43); 0.99
Chicken and ham pie – RR 1.25 (0.80-1.96); 0.43
Coleslaw – RR 1.13 (0.48-2.66); 0.76
 
Highest attack rates for coronation chicken and ham prepared by suspected source (foodhandler).
 
Adjusted analyses found only cornocation chicken was associated with illness:
Coronation chicken – RR 3 (1.9-4.8); <0.0001
SRSV visualized on EM in 2/5 samples.
 
A member of the catering staff attended a children’s party April 15th where there was a child with gastrointestinal illness.April 17th the staff member had vomiting and diarrhea, came to work, and was sent home. She returned on April 19th asymptomatic and helped prepare meals for the conference.
 
Power and sample size not reported.
1625_IL
Alexander WJ, 1986 91 Prospective controlled study
 
1, 2, 3, 4
To investigate a norovirus outbreak at a college campus. College campus in Jefferson County, Alabama in November 1981
 
N=92
Patient-control analysis of foods eaten and development of illness (Meal: Item – No. of discardant pairs (patients vs. controls); p value
Noon, Nov 15th: fried chicken – 2 vs. 4; NS
Noon, Nov 16th: chicken/dumplings – 2 vs. 8; NS
Noon, Nov 16th: corn – 6 vs. 3; NS
Noon, Nov 16th: BBQ beef – 3 vs. 0; NS
Noon, Nov 16th: lettuce – 11 vs. 2; 0.02<p<0.05
Evening, Nov 16th: lettuce - 7 vs. 1; NS
Noon, Nov 17th: mashed potatoes -4 vs. 1; NS
Noon, Nov 17th: lettuce – 8 vs. 4; NS
Evening, Nov 17th: lettuce – 9 vs. 2; NS
Serologic evidence of Norwalk virus infection.
 
Power and sample size not reported.
1935_IL
de Wit, M; 2007 92 Retrospective controlled study
 
1, 3, 4, 6, 7
To describe an outbreak of gastroenteritis caused by a baker infected with norovirus who continued to work in his bakery having washed his hands and disinfected countertops. Staff of a department in the Netherlands who attended a reception where the outbreak was reported. Median age 39 years; 45% female.
 
800-900 employees; 231 reported diarrhea or vomiting
Symptoms
Diarrhea and vomiting – 76%
Diarrhea only – 12%
Vomiting only – 12%
Median time to onset of symptoms – 31 hours
 
Symptomatic norovirus infection
All results OR(95% CI)
Univariate analysis

Coffee – 0.3(0.1-0.9)
Tea – 0.7(0.2-2.0)
Milk – 1.3(0.9-1.9)
Butter milk – 1.1(0.7-1.8)
Orange juice – 1.2(0.8-1.6)
Champagne – 1.6(1.1-2.3)
Cheese – 1.5(1.1-2.2)
Brie – 1.1(0.7-1.8)
Ham – 1.5(1.0-2.2)
Beef – 1.2(0.8-1.9)
Tuna salad – 1.6(1.1-2.4)
Salmon salad – 2.2(1.0-4.5)
Egg salad – 1.4(0.9-2.1)
Raisin roll – 0.9(0.6-1.3)
Increasing number of rolls – 2.0(1.6-2.4)
 
Multivariate analysis
Coffee – 0.4(0.1-0.8)
Raisin roll – 0.5(0.3-0.8)
Number of rolls – 2.0(1.5-2.5)
 
Intervention implemented
Sick food handlers excluded from work for 48hrs and reinforcement of hygiene measures
A case was defined as a member of the departmental staff who attended the reception and reported diarrhea (3 or more loose stools a day) or vomiting in the 72 hours following the reception. A control was defined as a member of the department staff attending the reception without diarrhea or vomiting in the 72 hours following the reception.
 
Norovirus infection was confirmed using RT-PCR
 
The estimated response rate for questionnaires among cases was nearly 100%. The estimated response rate among controls was 40-50%
 
Power and sample size not reported
4084_RA
MMWR;2007 93 Retrospective controlled study
 
1, 2, 3, 4
To identify the source of a restaurant outbreak. Subjects who ate at a Michigan restaurant in January/February 2006 during a norovirus outbreak. Cases – median age 40 years (range 1-92 years); 58.5% female.
 
364 patrons met case definition for the descriptive study. The case control study included 45 cases and 91 controls.
Symptomatic norovirus infection
All results in OR (95% CI)
Antipasti platter – 2.96 (1.08-8.14)
Garlic mashed potatoes – 4.05 (1.37-11.99)
 
Several food service workers reported to work ill including one line cook who vomited at the work station.
 
Interventions:
-Food prepared during January 27-30th was discarded
-Ill employees were excluded from work for at least 72 hours after symptoms had subsided.
-Facility was cleaned extensively.
Case for the descriptive February 3, 2006 and developed vomiting or diarrhea within 10-50 hours. A case for the employee was an employee with vomiting or diarrhea during that time period.
 
For the analytic study, case patron was someone who had eaten at the restaurant from January 28-29 and developed vomiting or diarrhea 10-50 hours after eating. A control was a patron with the same exposure but no gastrointestinal illness.
 
Power and sample size not reported.
046_IL
Rizzo C, 2007 94 Retrospective controlled study
 
1,2,3,4,6,7
To investigate risk factors for a norovirus outbreak in a resort. Resort in Puglia region of Italy during a three week period in July 2005.
 
400 guests during outbreak 150 guests available at the start of investigation and 41 (27.3%) cases identified.
 
N= 41 cases and 41 matched controls.
Risk factor – cases # (%) vs. controls # (%): OR (95% CI); p value
Only variables included in conditional logistic model have multivariate OR listed

Ice – 21 (51%) vs. 12 (29%): univariate OR 4.1 (0.9-7.1); 0.04
multivariate OR 16.4 (1.8-250.9); 0.04
Eggs – 2 (5%) vs. 8 (19%): univariate OR 2.3 (0.1-1.7); 0.12
Grilled sausage – 21 (51%) vs. 25 (61%): univariate OR 0.7 (0.2-1.7); 0.17
Ham – 1 (2%) vs. 5 (12%): univariate OR 2.8 (0.1-1.7); 0.09
Grilled meat – 11 (27%) vs. 15 (37%): univariate OR 3.5 (0.1-1.1); 0.06
Snacks – 20 (49%) vs. 19 (46%): univariate OR 0.1 (0.4-2.8); 0.15
Raw mussels – 22 (54%) vs. 13 (31%): univariate OR 3.9 (0.9-6.8); 0.04 multivariate OR 25.5 (1.5-442.9); =0.03
18/20 (90%) fecal samples were positive for norovirus by RT-PCR 3 samples confirmed GGII norovirus.
 
One matched control was selected for each case assuming 25% exposed controls, 80% power to detect OR 4.1, alpha error of 5%.
3_IL
Schmid, D; 2007 95 Retrospective controlled study
 
1, 3, 4, 6, 7
To identify the source of a norovirus outbreak at a telephone company. Cases were employees or external persons who ate lunch at the canteen of the telephone company in Austria and developed gastroenteritis.
 
325
Symptomatic norovirus infection - Attack rate
182/325 (56%)
 
Symptomatic norovirus infection
Demographic characteristics
Age – cases 38.4 years (SD 11.33) vs controls 34.5 years (SD 12.7); p=0.004
Female – RR 1.23 (95% CI 1.02-1.5); p=0.054
 
Working days
Univariate analysis: All results RR (95% CI); p value
Monday – 0.06 (0.02-0.2)
Tuesday – N/A
Wednesday – 18.82 (11.82-29.96); <0.001
Thursday – 2.14 (1.65-2.79); <0.001
 
Multivariate analysis: All results RR (95% CI)
Monday – 0.08 (0.02-0.25)
Tuesday – N/A
Wednesday – 3.05 (2.18-4.28)
Thursday – 1.89 (1.27-2.81)
 
Day-by-day food specific analysis
Univariate analysis: All results RR (95% CI)

Monday salad – N/A
Monday potatoes – 0.94 (0.09-10.17)
Tuesday potatoes – 0.66 (0.39-1.14)
Tuesday compote – 1.40 (0.77-2.54)
Tuesday salad – 2.51 (0.61-10.31)
Wednesday rice with beans –1.39 (1.04-1.85)
Wednesday salad – 3.44 (1.24-9.59)
Thursday semolina dumpling soup – 2.94 (1.57-5.52)
Thursday roast pork –1.72 (0.96-3.07)
Thursday potatoes –1.37 (0.81-2.32)
Thursday sauerkraut –1.86 (1.06-3.26)
Thursday salad – 1.04 (0.64-1.7)
 
Multivariate analysis: All results RR (95% CI); p value
Monday salad – N/A
Monday potatoes – 0.78 (0.05-13.67); 0.87
Tuesday potatoes – 0.80 (0.37-1.71); 0.57
Tuesday compote – 1.11 (0.50-2.43); 0.80
Tuesday salad – 2.19 (0.73-6.52); 0.16
Wednesday rice with beans –1.24 (0.96-1.61); 0.1
Wednesday salad – 2.82 (1.00-7.94); 0.05
Thursday semolina dumpling soup – 2.53 (1.32-4.83); 0.01
Thursday roast pork – 1.46 (0.55-3.88); 0.45
Thursday potatoes – 0.51 (0.29-0.92); 0.02
Thursday: sauerkraut – 1.91 (0.78-4.68); 0.16
Thursday salad – 1.77 (1.17-2.69); 0.01
 
Interventions implemented
Closure of kitchen
Gastroenteritis was defined as someone with symptoms of diarrhea (≥3 stools in 24 hours) and/or projectile vomiting after January 15, 2006.
 
Power and sample size not reported.
 
Most likely source of outbreak was a kitchen assistant who prepared the salad.
031_IL
Payne, J; 2006 207 Retrospective controlled study
 
1, 3, 4
To summarize an outbreak investigation into three norovirus outbreaks and a cluster of community cases. The primary outcome was identifying the source of norovirus illness. Cases of norovirus outbreak associated with a national submarine sandwich franchise restaurant in Michigan. The 3 outbreaks were at a school staff luncheon, publishing company staff luncheon and a social service organization luncheon. Community cases were also reported.
 
170 cases
Symptomatic norovirus infection
School staff luncheon – 23/29; 80%
Publishing company staff luncheon – 55/95; 58%
Social service organization luncheon – 9/18; 50%
Community cases – 25/28; 90%
 
Predominant symptoms
School staff luncheon – diarrhea (87%) and vomiting (74%)
Publishing company staff luncheon – diarrhea (94%) and vomiting (83%)
Social service organization luncheon – diarrhea (78%) and vomiting (78%)
Community cases – diarrhea (92%) and vomiting (80%)
 
Source of symptomatic norovirus infection
School staff luncheon – 22/23 cases reported eating lettuce; no specific food item was significantly associated with the illness
Publishing company staff luncheon – lettuce – 11.24(1.30-95.2); jalapeno peppers – 3.45(1.04-11.40); onions – 3.09(1.27-7.80)
Social service organization luncheon – no specific food item was significantly associated with the illness
Community cases – no specific food item was significantly associated with the illness
 
A food handler employed by the restaurant was identified as the source of illness. He had returned to work within a few hours of having symptoms of gastrointestinal illness while he was still excreting norovirus in the stools and lettuce was sliced each morning by him.
A case was defined as illness in a person who ate the suspect meal during the outbreak and became ill 856 hrs later with vomiting or diarrhea and two of the following: documented fever, abdominal cramps or nausea Cases were identified when the county health department was notified of the outbreak.
 
Power and sample size not reported
326_RA
Fretz, R; 2005 77 Retrospective controlled study
 
1, 2, 3, 6, 7
To identify risk factors for sporadic norovirus infections. All patients of general practitioners in German-speaking parts of Switzerland. Cases (mean age 32.7 years; median age 34 years; range 1.1-69.3 years) were subjects who resided in the study area who had an episode of diarrhea and/or vomiting, consulted a practitioner in the study area, had stool samples negative for Campylobacter, Shigella, Salmonella, and other gastroenteric pathogens, had stool samples positive for norovirus genogroup I or II. Cases excluded subjects <6 months or >75 years, patients with possible nosocomial disease, and patients who were part of a norovirus outbreak. Controls (mean age 33.2 years; median age 37.1 years; range 1.3-70.1 years) were identified through each patient, were the same sex and age group (defined as 5 year intervals over 5-20 years and 10 year intervals over 20-60 years), lived within 10 km of the case, and had not consulted a general practitioner for gastrointestinal illness or symptoms in the month prior to the questionnaire.
 
126 cases met study inclusion criteria. 73 matched case-control pairs.
Symptoms (study duration 2 years)
Diarrhea – 124/126 (98.4%).
Vomiting – 84/126 (66.7%).
Nausea – 85/126 (67.5%)
Fever – 57/126 (45.2%)
Headache – 45/126 (35.7%)
Abdominal cramps – 87 (69%)
Other – 46 (36.5%)
 
Mean duration of symptomatic illness
7.3 days (SD, 6.2 days; range 0.25-28 days)
 
Symptomatic norovirus infection
Multivariable analysis
Consumption of food and beverages OR (95% CI); p value

Mineral water – 1.00 (0.46-2.16); 1.00
Salad – 1.25 (0.34-2.65); 0.74
Raw berries – 0.75 (0.17-3.35); 0.71
Tap water – 1.33 (0.56-3.16); 0.51
Sweet beverages – 1.06 (0.55-2.05); 0.87
 
Personal contacts OR (95% CI); p value
Household with children ≤2 years) – 1.00 (0.29-3.45); 1.00
Household with children ≤ 5 years – 0.75 (0.26-2.16); 0.59
Household with children ≤ 10 years – 0.75 (0.26-2.16): 0.59
Household with children ≤ 65 years – 0.75 (0.17-3.35); 0.71
Household with children > 1 person – 1.50 (0.53-4.21); 0.44
Household with children > 2 person – 0.77 (0.34-1.75); 0.53
Household with children > 3 person – 0.71 (0.32-1.61); 0.53
Household with children > 4 person – 1.14 (0.41-3.15); 0.53
 
Symptomatic norovirus infection
ABO histo-blood group OR (95% CI); p value - conditional logistic regression
Type A: 1.34 (0.55-3.42); 0.49
Type B: 0.33 (0.07-1.65); 0.15
Type O: 1.00 (0.40-2.52); 0.49
Type AB: 1.50 (0.25-8.98); 0.65
Type A/AB: 1.44 (0.62-3.38); 0.39
Type B/AB: 0.63 (0.20-1.91); 0.40
 
Symptomatic norovirus infection
ABO histo-blood group OR (95% CI); p value – random effects logistic regression
Type A: 1.20 (0.55-2.61); 0.64
Type B: 0.28 (0.07-1.13); 0.07
Type O: 1.11 (0.51-2.45); 0.79
Type AB: 1.89 (0.35-10.2); 0.46
Type A/AB: 1.39 (0.64-3.00); 0.40
Type B/AB: 0.59 (0.21-1.70); 0.32
Power and sample size reported as 70 matched case-control pairs to detect an OR of 2.9 (alpha 0.05; power 0.80; 0.5 probability of an event in the exposed group).
 
Period between the start of symptoms and completion of the patient questionnaire averaged 29 days (median 24 days).
506_IL
Grotto, I; 2004 97 Retrospective controlled study To investigate an outbreak on an Israeli military base.
 
1, 3, 4
Soldiers at Israel Defense Force training center.
 
159: 84 males and 75 females. 40 cases and 44 controls for the case control study.
Risk factor of meals, selected food items, and dining facilities:
All results – OR (95% CI)
Breakfast Dec 20, 1999 – 1.68 (0.55-5.20)
Fresh vegetable salad that meal – 2.62 (0.99-6.96)
Lunch Dec 20, 1999 – 4.11 (0.96-24.52)
Fresh vegetable salad that meal – 4.38 (1.51-13.35)
Dinner Dec 20, 1999 – 0.59 (0.05-5.45)
Breakfast Dec 21, 1999 – 1.29 (0.49-3.43)
Vegetable salad at that meal – 2.86 (1.05-7.88)
Lunch Dec 21, 1999 – 0.70 (0.25-1.91)
Dinner Dec 21, 1999 – 0.15 (0.05-0.44)
Restaurant – 0.34 (0.13-0.92)
Eating at least one meal at a restaurant located off base on Dec 20-21 – 0.34 (0.13-0.92)
 
One food handler was reported being ill and vomiting 2 days before the outbreak. This food handler was not excluded from work and was not present during the iinvestigation.
Cases were defined as any base personnel who during the week of December 1926, 1999 suffered diarrhea (3 or more loose stools in 24 hours), vomiting or abdominal pain, with or without fever (>37.5 degrees Celsius). 576_IL
de Wit, M;2003 61 Retrospective controlled study (nested case-control study)
 
1, 3, 4, 6, 7
To identify risk factors for norovirus infection Patients registered at a general practice network in Netherlands. Cases were those persons identified in the community cohort with gastroenteritis and a matched control was selected from the cohort members without gastroenteritis at that time. Median age of case patients was 2 years. Other demographic characteristics were not reported.
 
152 case-control pairs
Symptomatic norovirus infection
All results OR(95% CI) unless otherwise noted
 
All case-control pairs
Univariate analysis
Poor food-handling hygiene (as a score) – 1.3(1.0-1.5); P<0.05
Low education level vs. intermediate education level – 1.9(0.9-4.0)
High education level vs. intermediate education level – 2.2(1.2-3.9)
Participant to day care center – 1.7(0.9-3.3)
Household member to daycare center – 2.0(1.0-3.9)
Household member to primary school – 1.6(1.0-2.7)
Pets in household – 0.6(0.4-1.0)
Cat as pet – 0.6(0.4-1.0)
1 household member with gastroenteritis vs. none – 3.7(1.7-8.0)
>1 household member with gastroenteritis vs. none – 13.1(3.9-34.7)
Child household contact – 5.2(1.8-15.3)
Adult household contact – 4.4(2.0-9.6)
Contact with person outside household with gastroenteritis – 11.4(4.727.3)
Consumption of fish in the week before onset of symptoms – 1.8(1.0-3.2)
Consumption of barbecued food in the week before onset of symptoms – 0.2(0.05-1.0)
 
Multivariate analysis
Poor food-handling hygiene (as a score) – 1.3(1.0-1.7); P<0.05
1 household member with gastroenteritis vs. none – 1.2(0.3-4.2)
>1 household member with gastroenteritis vs. none – 10.9(2.0-60.5)
Contact with person outside household with gastroenteritis – 12.7(3.151.8)
 
Population attributable risk (%) (based on multivariate odds ratios)
Poor food handling hygiene – 47
Number of household members with gastroenteritis – 17
Contact with person outside household with gastroenteritis – 56
 
<1 year to 4 years (105 case-control pairs)
Univariate analysis
Poor food-handling hygiene (as a score) – 1.2(0.9-1.5)
≤ 1 household members with gastroenteritis – 4.4(2.2-9.2)
Contact with person outside household with gastroenteritis – 17.7(5.161.1)
 
Multivariate analysis
Poor food-handling hygiene (as a score) – 1.2(0.9-1.7)
≤ 1 household members with gastroenteritis – 2.7(0.8-8.9)
Contact with person outside household with gastroenteritis – 10.9(2.254.6)
 
Population attributable risk (%) (based on multivariate odds ratios)
Poor food-handling hygiene (as a score) – 46
≤ 1 household members with gastroenteritis – 27
Contact with person outside household with gastroenteritis – 51
 
≤ 5 years (46 case-control pairs)
Univariate analysis
Poor food-handling hygiene (as a score) – 1.3(0.9-1.9)
≤ 1 household members with gastroenteritis – 15.0(2.0-113.6)
Contact with person outside household with gastroenteritis – 5.9(1.720.1)
 
Multivariate analysis
Poor food-handling hygiene (as a score) – 1.3(0.8-2.2)
≤ 1 household members with gastroenteritis – 1.1(0.1-15.9)
Contact with person outside household with gastroenteritis – 12.1(1.0147.3)
 
Population attributable risk (%) (based on multivariate odds ratios)
Poor food-handling hygiene (as a score) – 63
≤ 1 household members with gastroenteritis – 4
Contact with person outside household with gastroenteritis – 60
Samples were tested for norovirus by RT-PCR Cases and controls were matched by age, degree of urbanization, region and date of inclusion Selection of variables into the multivariable model was backwards manually, based on the log likelihood ratio; a significance level of 0.05 was used.
 
Food handling hygiene was determined using a questionnaire that included items on acquisition and preparation of food.
 
Power and sample size not reported
763_RA
Marks, P; 2003 98 Retrospective controlled study
 
1, 3, 4, 6, 7
To describe an outbreak of NLV gastroenteritis during which vomiting occurred in some, but not all, classrooms and thus investigate the importance of vomiting as a mode of transmission of NLV, and the likelihood that environmental contamination played a role in the spread of the outbreak. Children in a primary school and nursery in the UK. Age range 4-11 yrs.
 
492
Symptomatic norovirus infection – Attack rates (during the study period)
 
Based on sex [All results % (95% CI)]
Male – 30.4(25.1-36.2)
Female – 31.3(25.7-37.6)
 
Based on age group [All results % (95% CI)]
3-<4 yr – 20.0(9.5-37.3)
4-<5 yr – 25.9(16.3-38.4)
5-<6 yr – 44.8(32.7-57.5)
6-<7 yr – 52.3(37.9-66.2)
7-<8 yr – 39.0(27.6-51.7)
8-<9 yr – 28.3(18.5-40.8)
9-<10 yr – 27.0(18.2-38.1)
10-<11 yr – 22.2(13.7-33.9)
11-<12 yr – 16.7(8.3-30.6)
 
Vomiting episodes within classrooms as a risk factor [All results OR(95% CI) unless otherwise noted]
Attack rates increased with the number of vomiting episodes to which pupils were exposed (Chi-squared for linear trend – 37.8; P<0.01)
1 episode vs. none – Unadjusted: 2.7(1.6-4.5); Adjusted*: 5.1(2.2-11.6)
2 episodes vs. none – Unadjusted: 3.0(1.5-5.8); Adjusted*: 3.9(1.8-8.6)
3 episodes vs. none – Unadjusted: 10.4(4.8-22.4); Adjusted*: 14.6(5.936.5)
 
Exposure to another child vomiting as a risk factor [All results OR(95% CI)]
Unadjusted: 3.9(2.2-7.0); Adjusted*: 4.1(1.8-9.3)
 
Median time from exposure to onset of illness in days(during the study period)
3 pupils vomiting on the same day vs. vomiting occurring only once – 1 vs. 14; P<0.01
 
Symptomatic norovirus infection - Secondary attack rates (during the study period)
Adults – 17%
Children – 46%
Overall – 30%
 
(*Adjusted for sex, age and building in which the classroom was situated)
Cases were defined as follows:
- for those pupils who returned a questionnaire: those who reported either diarrhea or vomiting or both
- for those pupils who did not return a questionnaire: those who were absent from school with symptoms compatible with NLV infection
Secondary cases were defined as other household members reporting by questionanaire diarrhea or vomiting after a pupil had been ill.
 
Airborne transmission is implicated but in the discussion the authors state that aerosolization (eg droplets) from vomiting children may be the method of transmission.
 
Outbreak was confirmed using EIA or PCR for selected specimens
 
Completed questionnaires were returned for 289 pupils (response rate 59%)
 
Study period was 25 June to 16 July 2001
 
Power and sample size not reported
798_RA
Stegenga, J.; 2002 99 Retrospective controlled study
 
1, 3, 4
To examine the relationship between nurse staffing levels and the rate of nosocomial viral gastrointestinal infections in a general pediatrics population Patients on a general pediatrics ward in Toronto, Canada. Demographic characteristics not provided.
 
37
Symptomatic norovirus infection
All results Pearson correlation coefficient with norovirus gastroenteritis, P value
Monthly night patient-to-nurse ratio – 0.56; <0.05
Monthly day patient-to-nurse ratio – 0.50; <0.05
Monthly patient census – 0.51; <0.05
Monthly nursing hours per patient day: – 0.38; 0.14
 
Symptomatic norovirus infection at 72 hours (infections per 1000 patient days)
Nursing hours/patient-day<10.5 vs. >10.5 – 6.39 vs. 2.17; RR(95% CI) = 2.94(2.16-4.01)
 
All results preinfection period vs. non-preinfection period; P value
Mean nursing hours per patient day
12.5 vs. 13.0; <0.05
Mean nursing hours worked per patient day
390 vs. 376; <0.01
Mean patient census
31.7 vs. 29.5; <0.01
Day patient-to-nurse ratio
3.31 vs. 3.32; P>0.05
Night patient-to-nurse ratio 3.26 vs. 3.16; P<0.05
norovirus gastroenteritis was defined according to CDC definition
 
Analysis was done under the assumption of a 72 hr incubation period for norovirus gastroenteritis.
 
The cut-off point for 10.5 nursing hrs per patient day was chosen because the authors deemed this to represent a level of staffing that was inappropriately low, but occurred frequently enough to provide a comparison with more appropriate staffing levels.
 
The 72 hour period prior to each infection was considered as pre-infection period and all other periods were considered post infection. Overall, 92 days were defined as pre-infection period and 363 days were defined as non pre-infection period.
 
Power and sample size not reported
963_RA
Gotz, H; 2001 62 Retrospective controlled study
 
1, 3, 4
To describe an outbreak in which secondary transmission into households by individuals occurred Children and staff at 30 child centers (either a day care facility for preschool children or an after-school center for young children) in Sweden and their household contacts. Child center cases – 79 adults (mean age 41 yrs) and 114 children (mean age 5 yrs) Household cases – 58 adults (mean age 36 yrs) and 21 children (mean age 7 yrs)
 
775

Symptoms
All results adults vs. children - % reporting symptoms; P value
Diarrhea – 71.5 vs. 52.0; <0.01
Vomiting – 64.1 vs. 80.6; <0.01
Nausea – 96.8 vs. 93.1; 0.22
Stomach pain – 87.7 vs. 88.7; 0.82
Headache – 63.6 vs. 43.5; 0.01
Chills – 44.3 vs. 20.8; <0.01
Fever – 44.7 vs. 35.2; 0.20
Myalgia – 48.2 vs. 17.5; <0.01
 
Symptomatic norovirus infection - Primary attack rate
Adults vs. children – 68/127 vs. 74/386; P<0.01
Children 0-5 yrs old vs. 6-10 yrs old – 44/204 vs. 30/179; P=0.23
 
Symptomatic norovirus infection - Secondary attack rate
Adults vs. children – 11/59 vs. 40/312; P=0.23
Children 0-5 yrs old vs. 6-10 yrs old – 27/160 vs. 12/149; P=0.02
 
Risk factors for household transmission of symptomatic norovirus infection
All results RR(95% CI) unless otherwise noted
Children (vs. adults) – 3.8(1.9-7.6)
Exposure to vomiting – 2.4(1.0-5.5)
Exposure to diarrhea – 0.8(0.5-1.3)
Increased frequency of vomiting – P<0.01
Size of household – P=0.14
Onset of illness at child center (vs. onset of illness at home) – 0.9(0.61.6)
 
Median incubation period for primary cases
34 hours (range 2-61 hours)
 
Median serial interval (between a case in the chid center and the linked household cases)
Overall – 73 hours (range 4-198 hours)
Counting only the first case in each household – 59 hours (range 4-198 hours)
Truncating at 96 hours – 52 hours (4-96 hours)

Primary case: a person in the child center who became ill and who had diarrhea, vomiting or nausea during the first 3 days of the outbreak Secondary case: a person who became ill from day 4 through day 12 of the outbreak Secondary household case: a person who became ill at >6 h but <10 days after the onset of disease in the corresponding patient who acquired the infection in the child center.
 
NLV was confirmed using EM, used PCR for genotyping
 
Power and sample size not reported
 
524/775 subjects (68%) returned the questionnaire
1024_RA
Becker KM, 2000 100 Retrospective controlled study
 
1, 2, 3, 4, 6, 7
To investigate norovirus outbreak at a football game. Football game in Florida. Norovirus outbreak primarily involved members of the North Carolina football team during a game in Florida.
 
N=108 members of the North Carolina team and support staff interviewed.
54 with illness: 43 primary cases and 11 secondary cases.
Meal risk factor – Unadjusted RR (95% CI)
Lunch 9/18 – RR 4.1 (1.6-10.0)
Dinner 9/18 – RR 1.2 (0.7-2.2)
Late dinner 9/18 – RR 1.2 (0.8-1.8)
Breakfast 9/19 – RR 0.9 (0.6-1.5)
Lunch 9/19 – RR 1.1 (0.7-1.7)
 
Rate of attack among those who ate box lunch 9/18 – 62%
 
Lunch 9/18 food specific risk factor – OR (95% CI)
Sandwich – unadjusted OR 2.6 (1.2-5.5); adjusted OR 4.9 (1.3-18.9)
Apple – unadjusted OR 1.6 (1.1-2.3); adjusted OR 2.4 (0.6-9.3)
Candy bar – unadjusted OR 1.8 (1.0-3.2); adjusted OR 1.6 (0.5-5.0)
 
Rate of attack among those with ate sandwich – 71%
All 4 stool samples obtained from North Carolina patients were positive for norovirus like virus on EM. All 4 samples and ½ stool samples from players on Florida team were positive for norovirus-like virus of genogroup I on RT-PCR.
 
RT-PCR products had identical sequences.
 
Power and sample size not reported
1101_IL
Parashar, U; 1998 101 Retrospective controlled study
 
1, 3, 4
To determine the etiologic agent, source of infection and mode of spread of a gastroenteritis outbreak. Employees of a manufacturing company in Ohio. Demographic characteristics not reported.
 
325
Symptomatic norovirus infection - Food specific attack rates (at < 1 week after outbreak)
All results RR(95% CI)
Sandwiches – 14.1(2.0-97.3)
Ice – 1.5(1.0-2.3)
Tap water – 1.5(1.1-2.2)
Chips – 1.4(0.9-2.1)
Cookies – 1.4(0.9-2.1)
Bottled soda – 1.3(0.9-1.9)
Canned soda – 1.3(0.8-2.0)
 
One of the food handlers who prepared the sandwiches reported gastroenteritis that had subsided 4 days earlier
A case was defined by the presence of vomiting or diarrhea (≤ 3 loose stools in 24 hrs).
 
NLV was confirmed by EM and RT-PCR
 
Power and sample size not reported
1288_RA
McEvoy, M; 1996 102 Retrospective controlled study
 
1, 3, 4
To describe an outbreak of norovirus gastroenteritis. Passengers and crew of 4 cruises in the western Mediterranean. Median age of cases 55 years; 13/23 males
 
46 (23 cases and 23 controls)
Risk factors for symptomatic norovirus infection (matched pairs analysis)
All results OR; P value
Gala dinner – 0.20; 0.22
Salad – 1.00; 0.77
Fruit – 0.56; 0.42
Eggs – 0.50; 0.38
Table – 1.33; 1.00
Taps – OR not calculable; 0.24
Ice (tap water) – 0.56; 0.42
Teeth (tap water) – 1.00; 0.77
Pool – 0.71; 0.77
Chicken – 0.50; 0.39
Prawns – 0.29; 0.18
Meat – 1.14; 1.00
Cream – 0.67; 0.75
 
Interventions
1. Hygiene measures were introduced in the galley
2. When the passengers disembarked for a short period, the cabins were cleaned with a chlorine based disinfectant
3. Soft furnishings were removed for steam cleaning from all cabins whose occupants had reported illness. At the same time, the crew and staff quarters, including communal bathrooms and lavatories, were cleaned in the same way.
 
Response to outbreak
After control measures were implemented, fewer than 10 cases of diarrhea and/or vomiting were detected on each of the fifth and sixth cruises
A primary cabin case (the first case to have occurred in a cabin) was defined as a passenger on the ship from 27 May to 2 June with diarrhea (≤3 loose stools in a 24 hour period) and/or vomiting. Controls were matched to cases by sex and age (within 10 years)
 
Norovirus was identified by EM and RT-PCR in fecal specimens
 
277/1100 questionnaires were completed and returned.
 
Power and sample size not reported.
1410_RA
Sharp, TW; 1995 64 Retrospective controlled study
 
1, 3, 4, 6, 7
To identify risk factors for an outbreak onboard an aircraft carrier. Crew members aboard an aircraft carrier.
 
4500 male crew members. Questionnaire results available for 2,618 shipboard personnel. Mean age 27 years (range, 17- 59)
Symptomatic norovirus infection - Attack rates (n=4500)
13% with symptomatic infection
8% sought medical attention; almost all missed at ≤1 day work
 
Univariate analysis (n=2618)
All results variable – attack rate; unadjusted OR (95% CI)
Age range (years)
17-19 – 17.6%; Reference
20-29 – 14.3%; 0.93 (0.6-1.5)
30-39 – 11.5%; 0.73 (0.4-1.2)
40-59 – 9.3%; 0.57 (0.3-1.2)
Race
White – 14.3%; Reference
Black – 8.8%; 0.58 (0.4-0.85)
Other – 17.2%; 1.24 (0.9-1.74)
Rank
Junior enlisted – 13.8%; Reference
Senior enlisted – 10.7%; 0.74 (0.4-1.3)
Officers – 9.4%; 0.65 (0.4-1.09)
Number of persons in sleeping compartment
1-10 – 7.1%; Reference
11-50 – 8.6%; 1.23 (0.7-2.3)
51-100 – 15.5%; 2.39 (1.4-4.3)
>100 – 18.6%; 2.98 (1.7-5.3)
 
Multivariate analysis (n=2618)
All results variable – adjusted OR (95% CI)
Age (by year) – 0.98 (0.97-0.99)
Race
White – Reference
Black – 0.6 (0.3-0.9)
Other – 1.0 (0.7-1.3)
Number of persons in sleeping compartment
1-10 – Reference
11-50 – 1.1 (0.5-1.7)
51-100 – 2.2 (1.6-2.8)
>100 – 2.8 (2.3-3.4)
 
Pre-outbreak antibody levels and subsequent acute gastroenteritis
All results pre-outbreak antibody titer – No. developing illness/total No. (%)
<50 – 2/14 (14%)
50-200 – 9/28 (32%)
400-800 – 8/20 (40%)
1600-3200 – 11/35 (31%)
≤6400 – 2/12 (17%)
All – 32/109 (29%)
 
Pre-outbreak antibody levels and subsequent fourfold or more titer rise
All results pre-outbreak antibody titer – No. with fourfold or more titer rise/total No. (%)
<50 – 6/14 (43%)
50-200 – 12/28 (43%)
400-800 – 5/20 (25%)
1600-3200 – 9/35 (26%)
≤6400 – 2/12 (17%)
All – 23/109 (31%)
 
Pre-outbreak antibody levels and subsequent fourfold or more titer rise with acute gastroenteritis
All results pre-outbreak antibody titer – No. with fourfold or more titer rise and developing illness/total No. (%)
<50 – 2/14 (14%)
50-200 – 5/28 (18%)
400-800 – 4/20 (20%)
1600-3200 – 4/35 (11%)
≤6400 – 1/12 (8%)
All – 16/109 (15%)
Power and sample size not reported.
 
Gastroenteritis was defined as anyone reporting either vomiting or water stools with at least one of the following: nausea, fever, headaches, chills, or myalgias.
 
Gastroenteritis was associated with at least a fourfold increase in Norwalk virus antibody levels measured by ELISA. Norwalk virus like particles were also seen using immune EM in 2/6 stools.
1513_IL
Chadwick, PR; 1994 103 Retrospective controlled study
 
1, 3, 4, 6, 7
To determine risk factors for small round structured virus infection during an outbreak at an elderly care unit. Healthcare workers at an elderly care unit.
Cases – mean age 36 years (range 21-58 years).
Controls – mean age 39 years (range 18-59 years).
90% questionnaire responders were female.
 
103 questionnaires returned.
Clinical features
Overall attack rate – 34%
Attack rates among healthcare subspecialties
Nursing – 40%
Pharmacists – 34%
Doctors – 0%
 
Staff absent from work due to illness – 75%
Duration of absence – median 2 days (range 1-9 days)
 
Risk factors for symptomatic infection
Univariate analysis
Nearby vomiting – 50% exposed staff vs. 20% unexposed staff; OR 3.89 (95% CI 1.4-11); p=0.007
Number of exposures to nearby vomiting – p=0.032
Contact with ill patients – 42% exposed staff vs. 13% unexposed staff; OR 4.71 (95% CI 0.94-46); p=0.07
Number of close contacts with ill patients – p=0.023
Cleaning vomit – OR 1.96 (95% CI 0.46-9.8); p=0.49
Cleaning diarrhea – OR 4.67 (96% CI 0.49-225); p=0.22
 
Multivariate analysis
Nearby vomiting was the only significant risk factor
 
Interventions Implemented
Handwashing emphasized
Restricted transfers from affected wards
Ward closures
Staff cohorting
Disinfection with chlorine-based products
 
Attribute declining attack rates among subsequent wards to infection control measures
Case was a patient or staff at the hospital with vomiting or ≤2 loose stools in a 24 hour period.
 
Power and sample size not reported.
 
Aerosolization of vomit may have been important in infection transmission during the outbreak.
1555_IL
Reid, JA; 1988 104 Retrospective controlled study
 
1,3,4
To investigate an outbreak of NLV. Subjects affected by outbreak in a United Kingdom hotel in October of 1987.
 
Over 164 people affected – 40 staff, over 70 resident guests, and 54 people attending functions.
32 cases and 100 controls completed questionnaire for case-control study.
Symptomatic norovirus infection - Food specific attack rates
All results: Consumption vs. no consumption; p value
 
Function 2
*Smoked trout – 5/7 (71%) vs. 0/9 (0%); <0.005
Soup – 0/9 (0%) vs. 5/7 (63%); <0.005
 
Cold meats
*Ham – 1/7 (14%) vs. 4/7 (57%); NS
*Beef – 2/5 (40%) vs. 3/10 (30%); NS
*Chicken – 2/4 (50%) vs. 3/12 (25%); NS
*Tongue – ½ (50%) vs. 3/12 (25%); NS
*Turkey – 2/4 (50%) vs. 2/9 (22%); NS
*Pork – 1/1 (100%) vs. 4/14 (29%); NS
 
Turkey and rice – 5/11 (45%) vs. 0/5 (0%); 0.11
 
Salads
Coleslaw – 1/4 (25%) vs. 4/12 (33%); NS
*Waldorf – 5/10 (50%) vs 0/6 (0%); 0.09
*Tomato and cucumber – 3/10 (30%) vs 1/5 (20%); NS
*Mixed - 2/8 (25%) vs 2/7 (29%); NS
*Rice - 4/6 (67%) vs 1/10 (10%); 0.04
 
Function 3
*Mixed seafood – 22/28 (79%) vs 0 (0%)
Baked poussin – 21/27 (78%) vs 1/1 (100%); NS
Courgettes – 18/22 (82%) vs 4/6 (67%); NS
Cauliflower – 19/25 (76%) vs 3/3; NS
Black Forest gateaux – 19/25 (76%) vs. 3/3 (100%); NS
Cream topping – 16/20 (80%) vs. 6/8 (75%); NS
Cream (with coffee) – 9/12 (75%) vs. 13/16 (81%); NS
Cocoa almonds: 13/15 (87%) vs 9/13 (69%); NS
Table water: 6/8 (75%) vs 16/20 (80%); NS
*Foods prepared by chef who was still excreting virus 48 hours after his symptoms.
 
Cases were guest at the hotel from October 17-24 who had gastrointestinal disease defined by the presence of vomiting, or diarrhea (3 or more loose stools in 24 hours) or abdominal pain and nausea, or fever and either abdominal pain or nausea. Reported to management but who had not been interviewed.
 
Norwalk-like virus identified by EM.
 
Power and sample size not reported.
1847_IL
Iversen, AM; 1987 105 Retrospective controlled study
 
1, 3, 4
To identify the source of two outbreaks caused by a small round structured virus. Two outbreaks occurred in the banqueting suite of a London hotel.
 
First dinner -280 guests. Second dinner – 114 guests.
Symptomatic norovirus infection - Food specific attack rates:
All results –consumption vs. no consumption; p value
 
First outbreak
Melon – 197/220 vs. 0/5; 0.000006
Beef – 196/223 vs. 4/5; NS
Potatoes – 196/218 vs. 3/9; NS
Horseradish sauce – 142/161 vs. 58/67; NS
Blackforest gateau –184/207 vs. 16/21; NS
Cream – 180/202 vs. 19/26; NS
 
Second outbreak
Trout – 51/92 vs. 5/9; NS
Horseradish sauce – 31/35 vs. 25/39; 0.026
Vermicelli consommé – 54/66 vs. 2/8; 0.004
Duck – 55/70 vs. 2/5; NS
Potatoes – 52/68 vs. 4/6; NS
Ice cream soufflé – 53/67 vs. 3/7; NS
Case was someone with abdominal pain, nausea, vomiting, or diarrhea in a week after dinner.
 
Chef was likely source of outbreaks.
 
Power and sample size not reported.
1881_IL
White, KE; 1986 106 Retrospective controlled study
 
1, 3, 4, 6, 7
To conduct a foodborne outbreak investigation. Attendees at 8 banquets at a single Minnesota hotel.
 
383 attendees.
Symptomatic norovirus infection - Attack rate
220/383 (57%) developed gastroenteritis.
 
Food-specific attack rate
Univariate analysis – All results % ill among exposed vs % ill among unexposed; OR; p value
 
Banquet A
Potato salad – 57% vs. 30%; 3.2; 0.05
Fried chicken – 54% vs. 27%; 3.1; 0.06
Cranberry sauce – 86% vs. 34%; 11.6; 0.01
Fruit salad – 59% vs. 32%; 3; 0.07
 
Banquet B
Potato salad – 82% vs. 65%; 2.5; 0.04
Coleslaw – 84% vs. 57%; 4.0; 0.0007
 
Banquet C
Tossed salad – 56% vs. 13%; 9.0; 0.007
 
Multivariate analysis – All results RR; p value
Banquet A
Potato salad – 10.6; 0.010
Fried chicken – 4.1; 0.086
Cranberry sauce – 7.5; 0.062
Fruit salad – 7.7; 0.026
 
Banquet B
Potato salad – 2; 0.177
Coleslaw – 3.8; 0.004
 
Banquet C
Tossed salad – N/A
Case was defined as individual who developed diarrhea (≤ 3 loose stools within 24 hours) or vomiting within 3 days of consuming a meal prepared by food service of the hotel or after contact with primary case.
 
Power and sample size not reported
1921_IL
Kaplan JE, 1982 107 Retrospective controlled study
 
2, 4
To describe Norwalk oubreaks and assess how often Norwalk virus was implicated in outbreaks of acute nonbacterial gastroenteritis. Records of gastroenteritis outbreaks investigated for a viral cause by the CDC from 1976 -1980 and where serologic tests available. 7 additional norovirus outbreaks confirmed through 1980 at the NIH but not investigated by CDC. Overall
31/74 outbreaks (42%) investigated by the CDC were norovirus related
17/74 outbreaks (23%) with possible involvement of the norovirus
26/74 (35%) not due to norovirus virus
 
Analysis of confirmed norovirus outbreaks
norovirus outbreak characteristics
norovirus outbreaks: 38 confirmed including 7 not investigated by CDC 10 in camps and recreational areas, 7 in elementary schools 4 on cruise ships, 4 in nursing homes, 4 in colleges/universities, 4 in restaurants, 3 in small families, and 2 in larger communities.
3 in countries other than US, 4 on cruise ships at sea.
Outbreaks occurred all months of the year.
 
Source of norovirus outbreak
Common source of infection: 31 outbreaks.
17 possible vehicle of transmission: water in 13 outbreaks (municipal water systems in 2 outbreaks, semipublic water supplies in 7, stored water on cruise ships in 2, and recreational swimming in 2 outbreaks) and food in 4 (2 with oysters and 2 with salad).
 
Primary person to person transmission: 7 outbreaks Secondary person to person transmission (attack rates 4% to 32%): 20/ 23 common source and 3/3 person to person outbreaks for which evidence available.
Secondary attack rate highest among children <10 years of age in a single outbreak where information available.
 
Duration of norovirus outbreak
Outbreak duration: median 7 days (range, 1 day to 3 months) Of 24 common source outbreaks for which information available, 12 lasted 5-9 days.
Outbreaks of longer duration included 7 in which successive weekly outbreaks occurred among newly introduced populations and 1 nationwide epidemic associated with eating raw oysters.
Of the 5 perton to person transmitted outbreaks where information available, 4 lasted 5-9 days.
 
Number of infected persons and attack rates
Infected persons ranged from 2 to 2000.
Largest outbreaks in communities, schools, recreational areas, and on cruise ships (median, 348; range, 19-2000)
Smallest outbreaks in families and nursing homes (median, 19 cases; range 2-43)
All results: Common source outbreak vs. Person to person transimssion
No. affected persons – median, 236 (range, 6-2000) vs. median 38 (range 2-559).
Attack rates – median, 60% (range 23%-93%) vs. median 39% (range 31% to 42%).
Attack rates did not differ significantly with age or sex in the 6 outbreaks in which information was available.
 
Prevalence and duration of symptoms
All results ( #outbreaks which noted symptom): median % patients with symptom (range)
Nausea (30): 79 (51-100)
Vomiting (34): 69 (25-100)
Diarrhea (34): 66 (21-100)
Abdominal cramps (30): 71 (17-90)
Headache (22): 50 (17-80)
Fever (29): 37 (13-71)
Chills (14): 32 (5-74)
Myalgias (14): 26 (11-73)
Sore throat (7): 18 (7-32)
 
From 5 outbreaks, vomiting more frequent than diarrhea among children; and diarrhea more frequent than vomiting among adults. In 6 elementary school outbreaks, vomiting occurred in median 75% and diarrhea in median 46% of all children.
In 4 ourbreaks on cruise ships (affecting mostly adults), vomiting and diarrhea occurred in 51% and 85% cases respectively.
 
Duration of illness from 29 outbreaks ranged from 2 hours to several days. The mean (or median) time was 24- 48 hours in 19 outbreaks and 12- 60 hours in 26/28 outbreaks.
In 6 outbreaks, a small percent of persons (15% or less) were ill longer than 3 days
 
Of 22 outbreaks that recorded incubation period of illness, range was 477 hours
Mean (or median) incubation period was 24- 48 hours in 20/ 22 outbreaks.
 
Analysis of outbreaks possibly caused by norovirus virus
17 outbreaks occurred in all seasons of the year
11 in nursing homes, 3 in camps or recreational areas, 2 in elementary schools, and 1 in college.
Of 15 outbreaks in which information is available, 6 were common source infection (including 1 waterborne) and 9 primary person to person transmission (geographic clustering of cases in 2 outbreaks)
 
Secondary transmission (attack rates, 33% to 40%) in 2/3 common source outbreaks and 6/6 person to person outbreaks where information available
 
Outbreaks in the possibly norovirus virus category similar to in the confirmed norovirus category in duration of illness, prevalence of symptoms, and incubation period
 
All results: % (No. with characteristic/total number of outbreaks) among those with Norwalk infection vs. possibly Norwalk infection vs. not Norwalk infection
Duration of illness from 12 to 60 hours: 93 (28) vs. 92 (12) vs 84 (19)
Vomiting ≤ 50% cases: 89 (27/30) vs. 90 (10/17) vs. 50 (18/26)
Diarrhea ≤ 50% cases: 74 (27) vs. 70 (10) vs. 94 (18)
Headache ≤ 50% cases: 50 (18) vs. 25 (4) vs. 38 (13)
Incubation period from 24 to 48 hours: 91 (22) vs. 80 (5) vs. 78 (9)
 
Analysis of norovirus negative outbreaks
26 outbreaks occurred all months of the year 5 in nursing homes, 5 in restaurants, 4 in residential communities, 4 on cruise ships, 3 in hospitals, 2 in camps or recreational areas, and 2 in colleges.
 
14/21 outbreaks in which information was available were relate to a common source; 7 were waterborne an 3 were foodborne (salads) 7 outbreaks were primary to primary person to person transmission; geographic clustering was found in 2 of these.
Secondary transmission (attack rates 11% to 48%) in 7/7 common source outbreaks and in 2/2 person to person outbreaks for which information was available
 
Outbreaks not due to norovirus virus similar to those due to norovirus in duration of illness, prevalence of symptoms, and incubation period
Common source of infection if a vehicle of transmission was incriminated by epidemiologic analysis or if the peak onset of illness occurred during the first 2 days of the outbreak.
 
Primary person to person transmission presumed when no vehicle of transmission identified and when the peak onset of illness occurred after the second day of the outbreak; this was shown in some outbreaks by geographic clustering of cases.
 
Secondary person to person transmission was evidenced in both types of outbreaks by the finding of illness in family members or roommates not exposed to the primary location of the outbreak.
 
Incubation period determined by measuring either the interval between exposure to a common source and onset of illness or the intervals between onset of illness in primary and secondary cases.
 
Serologic testing by RIA and results of stool testing by immune EM or RIA/
 
An outbreak of gastroenteritis was considered to be caused by norovirus if at least 50% of the serum pairs from cases had a fourfold or greater rise in Norwalk antibody titer between acute and convalescent phases.
 
Power and sample size not reported.
2077_IL
Blanton LH, 2006 111 Descriptive Study
 
1, 2, 3, 4
To describe epidemiologic data from outbreaks of acute gastroenteritis occurring between July 2000 and June 2004 where samples were sent to the CDC. 226 confirmed outbreaks.
 
184 (81%) had CaCV detected.
 
Genogroup II norovirus strains were the most abundant (79%), followed by genogroup I norovirus strains (19%)
CaCV
Settings
65% of CaCV outbreaks in nursing homes, retirement centers, and hospitals
38% outbreaks in schools and day-care centers
58% outbreaks in vacation settings including cruise ships
Transmission
Person to person transmission (55%) vs. foodborne transmission (18%); p<0.001
 
norovirus
During 2002-2003 CaCV season, Farmington Hills sequivar was responsible for 36% all confirmed norovirus outbreaks and 44% of all GII outbreaks
RT-PCR used.
 
Power and sample size not reported.
371_IL
Mattison, K; 2007 112 Basic Science Study
 
Not applicable (N/A)
To assess virus survival in foods and on sufaces. FCV was used as a surrogate for norovirus to investigate its survival Food (lettuce, strawberry, ham) and metal surfaces. Study was conducted in Canada.
 
N/A
Survival of virus
At 30 min
Lettuce – 20%
Strawberry – 1%
Ham – 43%
Metal disk – 11%
At 7 days
There was a signifiant reduction in viral titer after 7 days for all samples at both room temperature (RT) and 4°C (P<0.05).
 
Comparison of virus survival at RT and 4°C (on day 7)
Lettuce – undetectable at RT; 1% survival at 4°C; statistical differences were not reported
Strawberry – undetectable at both RT and 4°C; survived for 5 days at 4°C, compared with survival of 1 day at RT; statistical differences were not reported
Ham – P>0.05
Metal disk – P>0.05
 
Comparison of virus survival among the different samples
The survival on ham was significantly greater when compared to all other surfaces at both temperatures (P<0.05)
Power and sample size not reported 154_RA

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