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

GRADE Table Q1 What person, virus or environmental characteristics increase or decrease the risk of norovirus infection in healthcare settings?

Person characteristics

Environmental characteristics

Comparison Outcome Quantity and type of evidence Findings Starting grade Decrease GRADE Increase GRADE GRADE of Evidence for Outcome Overall GRADE of Evidence Base
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Institution characteristics Symptomatic norovirus infection* 2 OBS 82, 99 An increase in average length of stay was an independent protective factor, general medicine ward and geriatric ward were independent risk factors in 1 OBS in the healthcare setting. Number of beds in a unit, having a previous outbreak, month following outbreak and acute care unit were possible risk factors. Surgical and mental health wards were not risk factors 82
Nurse understaffing was a possible risk factor in 1 OBS in a pediatrics ward 99
Low 0 0 0 −1 0 0 0 0 Very Low Very Low
Pets Symptomatic norovirus infection* 1 OBS 61 Pets in household and cats as pets were not risk factors in 1 OBS in the community setting 61 Low 0 0 0 −1 0 0 0 0 Very Low Very Low
Diet † Symptomatic norovirus infection* 23 OBS61, 77, 80, 81, 84, 86, 89 95, 97, 100-
102 104− 107 207 and 1 DES111
Of 17 norovirus outbreaks in 1 OBS where a possible vehicle of transmission was identified, water was implicated in 13 (municipal water systems in 2, semipublic water supplies in 7, stored water on cruise ships in 2, and recreational swimming in 2); and food in 4 (2 with oysters and 2 with salad) 107
 
Person to person transmission (55%) occurred more often than food transmission (18%) in 1 DES111
 
Coffee and raisin roll were independent protective factors and the number of rolls eaten was an independent risk factor in 1 OBS in the community setting where a baker continued to work despite being infected 92
 
Poor food-handling hygiene was independent risk factor in 1 OBS in the community setting 61
 
Lettuce, jalapeno peppers and onions were possible risk factors in 1 OBS in the community setting. A food handler who returned to work within a few hours of illness was identified as the source 207
 
Sandwiches, ice and tap water were possible risk factors in 1 OBS in the community setting. A food handler was implicated 101
 
Salad on Wednesday and Thursday, semolina dumpling soup on Thursday were independent risk factors and potatoes on Thursday were independent protective factors in 1 OBS in the community setting 95
 
Antipasti platter and garlic mashed potatoes were possible risk factors in 1 OBS in the community setting 93
 
Any salad, pasta salad, potato salad, vegetable salad, condiments, dips, cheese and bread were possible risk factors in 1 OBS in the community setting 86
Low 0 0 0 0 0 0 0 0 Low
Symptomatic norovirus infection* 23 OBS61, 77, 80, 81, 84, 86, 89, 95, 97, 100-102, 104-107, 207 and 1 DES111 Vegetable
salad was a possible risk factor in 1 OBS in the community setting. A food handler was the source of the outbreak 97
 
Eating smoked trout and rice salad and not eating soup were possible risk factors in 1 OBS in the community setting 104
 
Melon and vermicelli consommé were possible risk factors in 1 OBS in the community setting. Horseradish sauce was a possible risk factor in one outbreak reported in the study 105
 
In 1 OBS that reported outbreaks at banquets, potato salad, coleslaw and fruit salad were independent risk factors, cranberry sauce and tossed salad were possible risk factors 106
 
Lettuce was a possible risk factor in 1 OBS in the community setting 91
 
Ice and raw mussels were independent risk factors in 1 OBS in the community setting 94
 
Turkey salad, tuna salad and any salad were possible risk factors in 1 OBS. A possibly infected food handler was implicated 89
 
Coronation chicken was an independent risk factor in 1 OBS 90
 
Sandwich was an independent risk factor in 1 OBS 100
 
Scalloped potatoes, chicken and chocolate cheese roll were possible risk factors in 1 OBS 80
 
Rice salad with cocktail sauce was a possible risk factor in 1 OBS 81
 
Drinking water from the hospital water supply was not associated in 1 OBS 87
 
Beef, cheese, egg, ham, lamb, tuna sandwiches, soup, hot chocolate and coffee were found to be possible risk factors in 1 OBS 84
 
None of the foods were found to be risk factors in 2 OBS 77,102
                   
Survival of CaCV 1 BAS 112 Ham was a possible risk factor in 1 BAS 112 Very Low 0 0 0 0 0 0 0 0 very Low
Proximity to infected persons Symptomatic norovirus infection* 8 OBS 61, 62, 64, 79, 83, 88, 98, 103 and 1 DES111 Exposure to more than one household member with gastroenteritis was an independent risk factor overall, but not when divided into two groups of age < or ≥5 years in 1 OBS in the community setting. Contact with person outside household with gastroenteritis was an independent risk factor overall and in the two age-groups 61
 
> 50 persons in a sleeping compartment was an independent risk factor in 1 OBS among aircraft crew members. ≤ 50 persons was not a risk factor 64
 
Exposure to vomiting and increased frequency of vomiting were possible risk factors in 1 OBS in the community setting. Exposure to diarrhea and the size of the household were not risk factors 62
 
Exposure to vomiting and increased frequency of vomiting were independent risk factors in 1 OBS in the community setting 98
 
Distance from the vomiter was a possible risk factor in 2 OBS in the community setting 83,88
 
Nearby vomiting was an independent risk factor in 1 OBS among healthcare workers. Number of exposures to nearby vomiting and number of close contacts with ill patients were possible risk factors 103
 
Having an ill contact was a possible risk factor in 1 OBS 79
 
Person to person transmission (55%) occurred more often than food transmission (18%) in 1 DES 111
Low 0 0 0 0 0 +1 +1 0 High High
Time to illness 1 OBS 98 Significantly decreased with exposure to increased frequency of vomiting in 1 OBS in the community setting 98 Low 0 0 0 −1 0 0 0 0 Very Low

RCT – randomized controlled trial; OBS – observational study (prospective or retrospective controlled); DES – descriptive study (case series, case report, uncontrolled data in an observational study); BAS – basic science study
* These outcomes are considered the most critical by the guideline developers.
** These modifiers can impact the GRADE by 1 or 2 points † Rules for “not a risk factor” were not applied

Note: Definitions: "Independent risk factor" implies a variable was significant in a multivariate analysis; "possible risk factor" implies (1) it was significant in a univariate analysis and a multivariate analysis was not performed, or (2) it was significant in a univariate analysis but not in the multivariate analysis, but there were <10 events per variable examined in the multivariate analysis; "not a risk factor" implies that (1) it was not significant in a univariate/multivariate analysis when only one analysis was reported, and (2) there were > 10 events per variable examined in the univariate or multivariate analysis.

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