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Investigation of Gastroenteritis on the Royal Odyssey

CDC's investigation of Gastroenteritis on the Royal Odyssey Cruise Ship, March 4-14, 1997

 

This is the first of two investigations conducted on the Royal Odyssey. The report for the March 25-April 4, 1997 cruise is pending and will be available when completed.

Background

On March 13, 1997, the Vessel Sanitation Program (VSP), National Center for Environmental Health, Centers for Disease Control and Prevention (CDC) notified the Foodborne and Diarrheal Diseases Branch (FDDB), CDC of an outbreak of gastroenteritis among passengers and crew members on the Norwegian Cruise Line ship, the Royal Odyssey. In accordance with statutory requirement (Title 42, United States Code of Federal Regulations), ship officials had contacted VSP 24 hours before docking at a United States port and provided information on diarrheal illness among passengers and crew occurring during the cruise. The cruise occurred between March 4 though 14, with the following itinerary:

Date Port

March 4: Embarkation, Miami

March 5-6: at sea

March 7: Tortola

March 8: St. Barts

March 9: St. Kitts

March 10: St. John

March 11: San Juan

March 12: at sea

March 13: Great Stirrup Cay

March 14: Disembarkation, Miami

On March 13, the captain of the Royal Odyssey reported that over the 10-day cruise, 33 (4.4%) of 755 passengers and 8 (2.1%) of 375 crew had been seen at the infirmary for gastrointestinal illness characterized predominantly by vomiting and diarrhea, with 3 to 20 bowel movements occurring per 24-hour period. Some patients reported fever and abdominal cramps, but there had been no bloody or mucoid diarrhea observed. Five patients were hospitalized in the ship's infirmary, receiving intravenous fluids for rehydration.

Based on these reports (greater than 3% of passengers and crew members reporting diarrhea during the cruise), members of FDDB arranged to meet one of the inspectors from VSP in Miami to board the Royal Odyssey at 0700 hours on March 14 and assist with epidemiologic and environmental investigations. On March 13, epidemiologists from FDDB departed for Miami. The purpose of this investigation was to determine the etiology of the outbreak, the extent of the outbreak among passengers and crew, and the possible sources of infection, and to make recommendations to prevent future illnesses.

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Methods

Cohort studies were conducted among passengers and crew members using data gathered from two standard CDC questionnaires (one for passengers and one for crew members) faxed to the ship for distribution on March 13, the evening before disembarkation. The questionnaire addressed possible risk factors such as cabin and dinner seating assignment, shore excursions, and consumption of ship's water.

For this investigation, a case of gastroenteritis was defined as vomiting or diarrhea (3 loose stools in a 24-hour period) in a passenger or crew member aboard the Royal Odyssey with onset between March 4 and 14. Well passengers or crew members were persons reporting no gastrointestinal symptoms during the 10-day cruise. Persons reporting some gastrointestinal symptoms but whose illness did not meet the case definition were classified as having indeterminate illness and were excluded from further analysis. Serum and stool samples were collected from ill and well passengers and crew members by CDC investigators on March 14 for routine bacterial and viral testing. Rectal swabs were transported in Cary-Blair medium to CDC and examined for bacterial pathogens (Campylobacter, Salmonella, Shigella, Vibrio, toxigenic Escherichia coli, and Yersinia enterocolitica). Whole stools were tested for small round structured virus (SRSV) using electron microscopy (EM) and polymerase chain reaction (PCR) analyses.

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Results

Case finding

Questionnaires were collected on March 14 from 735 (97%) passengers and 374 (99.7%) crew members. We identified 303 (41%) ill passengers and 85 (23%) ill crew members with illness meeting the case definition, and 345 (47%) passengers and 243 (65%) crew members who were well; 87 (12%) passengers and 46 (12%) crew members had indeterminate illness and were excluded from further analysis (Table 1). Illness was characterized predominantly by diarrhea (88%), nausea (87%), abdominal cramps (83%), vomiting (72%), headache (70%), and fever (51%); bloody stools (6%) were uncommon (Table 2). Dates of illness onset ranged between March 4 and 14, with peak date of onset for passengers and crew members on March 12 (Figures 1 and 2). Among 141 ill persons who had recovered by the time they completed the questionnaire, the mean number of days ill reported was 2 days (range, <1 to 7).

Cohort studies

Higher gastroenteritis attack rates were observed among passengers who had consumed any of the ship's potable water (tap water) compared with passengers who had not (Table 3); 292 (49%) of 597 passengers who had consumed any tap water became ill, compared with 10 (26%) of 38 passengers who had not consumed any tap water [relative risk (RR)=1.86, 95% confidence interval (CI)=1.08-3.18]. In addition, dose-response effects were noted among passengers, with increased consumption of tap water associated with increased attack rates of gastroenteritis (2 for trend=19.38, p<0.001). There were no differences between gastroenteritis attack rates when comparing passengers who had or had not consumed any drinks containing ice during the cruise (RR=0.1.02, CI=0.69-1.51). Dose-response effects resulting in higher gastroenteritis attack rates were observed, however, with an increasing number of drinks containing ice consumed per day (2 for trend=8.37, p=0.004). Consumption of bottled water only, compared with bottled water and/or tap water, appeared to be protective against illness; 4 (19%) of 21 passengers who consumed only bottle water became ill, whereas 299 (48%) of 619 passengers who consumed bottled water and/or tap water became ill (RR=0.39, CI=0.16-0.96). There were no differences in attack rates when comparing dining or cabin assignments, or participation in or eating during any shore excursion.

Gastroenteritis attack rates were also higher among crew members who had consumed any tap water compared with crew members who had not (Table 4); 62 (37%) of 170 crew members who had consumed any tap water became ill, compared with 18 (20%) of 91 crew members who had not consumed any tap water (RR=1.84, CI=1.17-2.92). Among crew members, consumption of bottled water only appeared to be pSrotective against illness; only 16 (21%) of 75 crew members who had consumed only bottled water became ill, compared with 62 (37%) of 170 crew members who had consumed bottled water and/or tap water (RR=0.58, CI=0.36-0.94).

Laboratory Investigation

Rectal swabs were collected from 10 ill persons (7 passengers, 3 crew members), whole stool samples from 6 ill persons (4 passengers, 2 crew members), and serum from 14 ill persons (11 passengers, 3 crew). Eight serum samples and 1 whole stool were also collected from well persons. There were no bacterial pathogens identified from rectal swabs. SRSV particles were identified by EM in the whole stool of all 4 ill passengers tested, 1 of 2 ill crew members tested, and the 1 well passenger tested. SRSV was identified by PCR from the whole stool of 3 of 4 ill passengers tested, no ill crew members, and the 1 well passenger tested.

Environmental Investigation

During this cruise, water was bunkered in Miami (3/4), Tortolla (3/7), St. Kitts (3/9), San Juan (3/11), and Miami (3/14). On the Royal Odyssey, bunkered water is sporadically tested for the presence of total coliform bacteria using the Millipore® test, a membrane filter test that indicates the presence or absence of coliform bacteria. From potable water chlorine analyzer records, potable water chlorine levels were observed to be appropriate (between 1.0 and 3.0 ppm) at the distribution system level during the entire cruise, never dropping below the 0.2 ppm minimum requirement. Although the bunkered water was not tested for coliforms at St. Kitts on March 9, the water was chlorinated at 3.5 ppm because of its "dark" appearance and "salty" taste. Ship records revealed that on March 10, one routine sample from an ice sink was positive for coliforms by the Millipore test. Inspection of the galleys revealed good food handling and storage practices. Inspection of the potable water system and records revealed compliance with VSP regulations (see VSP report.) Analysis of samples collected and tested by VSP from the potable water distribution system (n=2) and the ice sink mentioned above (n=2) on March 14 were negative for coliforms and E. coli.

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Discussion

A large outbreak of gastroenteritis caused by a small round structured virus (SRSV) occurred among passengers and crew on the cruise ship Royal Odyssey during the Eastern Caribbean cruise, March 4 through 14, 1997. SRSV, formally called "Norwalk" or "Norwalk-like" virus, causes an acute, usually self-limited gastroenteritis characterized by nausea, vomiting, diarrhea, and abdominal pain lasting 24 to 48 hours. The epidemic curve for this outbreak supports a point source of exposure. The questionnaire distributed to passengers and crew revealed a statistical association between consumption of the ship's tap water and illness, but no deficiencies were noted by VSP in the ship's potable water system. The source of this outbreak is still being investigated.

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Recommendations

1. Report any diarrheal illness (including zero cases) on a daily basis, beginning March 14, to Vessel Sanitation Program in Miami.

2. Exclude any food handlers with current vomiting or diarrhea, a history of vomiting or diarrhea within the last 48 hours, or a history of vomiting or diarrhea and still taking antidiarrheal medications from duty for the duration of the illness and until all antidiarrheal medications have been discontinued.

3. Reinforce the importance of good handwashing to all crew members.

4. Consider testing all water before bunkering for coliforms (fecal contamination) as a proxy for the potential presence of SRSV.

5. Continue to investigate sources of contamination for this outbreak. This includes evaluating sources of bunkered water and water processing practices aboard the Royal Odyssey (VSP); investigating improved methods of detecting SRSV in water; and evaluating the efficacy of routine water chlorination practices in inactivating SRSV on cruise ships (Division of Viral and Rickettsial Diseases, CDC).

M. Kathleen Glynn, DVM, MPVM

Epidemic Intelligence Service Officer

Eric D. Mintz, MD, MPH

Chief, Diarrheal Diseases

Epidemiology Section

Foodborne and Diarrheal Diseases Branch Foodborne and Diarrheal Diseases Branch

Division of Bacterial and Mycotic Diseases Division of Bacterial and Mycotic Diseases

National Center for Infectious Diseases

Centers for Disease Control and Prevention

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Tables

Table 1. Gastrointestinal illness attack rate, Royal Odyssey cruise, March 4-14, 1997
CharacteristicTotal (%) Passengers (%)Crew (%)
Persons on board (as reported by Captain) 1130755375
Completed Questionnaires1109 (98)735 (97)374 (99.7)
Ill Persons 409 (38)303 (41)85 (23)
Persons with Indeterminate illness 133 (12)87 (12)46 (12)
Number of ill visiting ship's doctor/ Number responding76/409 (19)49/321 (15)27/88 (31)
Numbers still ill at end of cruise/ Number responding 175/344 (51)143/259 (55)32/67 (48)

 

Table 2. Characterization of clinical illness (from 303 ill passengers and 85 ill crew members), Royal Odyssey cruise, March 4-14, 1997
SymptomIll Passengers / no. Responding (%)Ill Crew / No. Responding (%) Total Ill / No. Responding (%)
Diarrhea246/282 (87)70/77 (91)316/359 (88)
Nausea253/277 (91)34/52 (65)287/329 (87)
Abdominal Cramps 221/261 (85)49/63 (78)270/324 (83)
Vomiting197/261 (75)30/51 (59)227/312 (72)
Headache178/250 (71)31/53 (58)209/393 (70)
Fever110/206 (53)19/45 (42)129/251 (51)
Sore Throat37/215 (17)14/50 (28)51/265 (19)
Bloody Stool 7/190 (4)6/44 (14)13/234 (6)

 

Table 3. Gastroenteritis attack rates among passengers associated with exposure to selected risk factors, Royal Odyssey cruise, March 4-14, 1997
Risk Factor No. Ill/No. Exposed (%)No. Ill/ No. not exposed (%)RR (CI) p-vaule
Consumed any Tap Water 292/597 (49)10/38 (26)1.86 (1.08-3.18)0.01
Consumed any Drinks with Ice284/596 (49)14/30 (47)1.02 (0.69-1.51)0.93
Consumed Bottled Water only4/21 (19)299/619 (37)0.39 (0.16-0.96)0.02

 

Table 4. Gastroenteritis attack rates among crew members associated with exposure to selected risk factors, Royal Odyssey cruise, March 4-14, 1997
Risk FactorNo. Ill / No. Exposed (%) No. Ill / No. not Exposed (%) RR (CI) p-vaule
Consumed any Tap Water 62/170 (37)18/91 (20)1.84 (1.17-2.92)0.008
Consumed bottled Water only 16/75 (21)62/170 (37)0.58 (0.36-0.94)0.03

 

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