An Outbreak of Enterotoxigenic E. Coli aboard the M/V Caronia, March 24 - April 5, 2002
An Outbreak of Enterotoxigenic E. Coli aboard the M/V Caronia, March 24 - April 5, 2002
Backgrounder
- On April 2, 2002, Dr. Elaine Cramer of the Vessel Sanitation Program (VSP), National Center for
Environmental Health (NCEH), notified the Foodborne and Diarrheal Diseases Branch (FDDB), Division of
Bacterial and Mycotic Diseases (DBMD), National Center for Infectious Diseases (NCID) of a possible
outbreak of gastrointestinal illness aboard the cruise ship M/V Caronia. In accordance with illness
reporting requirements outlined in the Vessel Sanitation Program Operations Manual 2000, the ship’s
physician reported to the VSP gastrointestinal illness in 90 (15%) of 621 passengers and 15 (4%) of 395
crew members by the 9th day of a 12 day cruise. The itinerary of the ship was as follows:
- March 24 Passenger embarkation, Acapulco, Mexico
- March 25 At sea
- March 26 Puerto Quetzal, Guatemala
- March 27 At sea
- March 28 Puntarenas, Costa Rica
- March 29 At sea
- March 30 At sea through Panama Canal
- March 31 San Blas Island, Panama
- April 1 San Andres Island, Colombia
- April 2 At sea
- April 3 Montego Bay, Jamaica
- April 4 At sea
- April 5 Passenger disembarkation, Fort Lauderdale, FL
- On the basis of higher-than-expected (>3% of passengers or crew) and increasing numbers of passengers
and crew reporting gastroenteritis, Cunard Line Limited, collaborated with CDC to conduct an epidemiologic,
laboratory, and environmental investigation of the outbreak. On April 3, Dr. Tom Chiller (EIS Officer,
FDDB, DBMD, NCID) and Commander Jaret Ames (VSP, NCEH) traveled to Montego Bay, Jamaica, to board the
ship and initiate an epidemic investigation on day 10 of the cruise.
- Objectives
- The objectives of the investigation were to:
- 1. Identify the etiologic agent(s) associated with the outbreak;
- 2. Determine the source(s) of spread of illness among passengers and crew;
- 3. Formulate interventional strategies to control the outbreak and prevent a recurrence.
Methods
- Epidemiological Investigation
- Case definition
- A case of gastroenteritis was defined as a passenger or crew member with diarrhea (3 or more loose
stools in a 24-hour period) or vomiting plus 1 other symptom (e.g. fever, abdominal cramps, headache,
muscle aches, or sore throat) with onset occurring between March 24, 2002, day 1 of the cruise, and April
4, 2002, day 11 of the cruise. A secondary case was defined as a passenger or crew member who met the case
definition and who developed illness at least 48 hours after a cabin mate. Secondary cases were excluded
from further analyses. Well people were defined as passengers or crew reporting no gastrointestinal
symptoms on the questionnaires during the first 10 days of the cruise. People who reported a
gastrointestinal illness, but who did not meet the case definition, were classified as having
indeterminate illness and were excluded from the cohort study.
- Records Review
- The gastrointestinal illness (GI) log, from March 22 – April 3, from the ship’s infirmary was
reviewed. Cases from the GI log meeting the case definition were used to generate a preliminary epidemic
curve to determine the most likely exposure period. Hypotheses as to the cause of illness were generated
by reviewing self-administered food history questionnaires completed by ill passengers who were treated
in the infirmary. Menus and daily passenger activities were reviewed with the Executive Chef and the Food
and Beverage Manager. All on-board restaurants and other areas where food was served were identified.
Dates of shore excursions and description of food served ashore were obtained.
- Passenger Survey
- A standardized passenger questionnaire, based on ship menus, shore excursions, and a likely period of
exposure determined by the epidemic curve, was distributed to the each of the 621 passengers on April 4th
by placing it under the cabin doors. All 395 crew also received a modified questionnaire. Interviewees
were asked about demographic information, risk factors for illness, and asked to select food items from a
list that they may have eaten during specific meals in the exposure period. Questionnaires were returned
to the reception desk on board the ship before passengers disembarked.
- Statistical Methods
- Data were entered and analyzed using Epi Info version 6.04 software. Descriptive and cohort analyses
of disease onset were based on returned questionnaires from ill passengers and crew who met the case
definition. Baseline characteristics of passengers and crew were described by frequencies and percentiles
for categorical variables and ranges of values for continuous variables. Univariate analysis was performed
using relative risks with 95% confidence intervals (CIs) to test for differences in risk between ill and
well individuals. A two-tailed p-value of < 0.05 was considered statistically significant. A cohort study
was conducted based upon the entire data set. Exposure variables were coded dichotomously; foods were
grouped according to specific meals (lunch on day 3) or specific foods (any chicken consumed during the
study period). Exposure variables included shore excursions, ship’s water, ice, and food items from meals
throughout the selected exposure period.
- Laboratory Investigation
- Prior to arrival of CDC representatives at the ship, the ship’s physician organized collection of 12
stool samples from ill passengers and crew, and stored the specimens in the infirmary refrigerator. After
arriving, 8 additional stool samples from ill passengers and crew were collected. Samples from all stools
were put into Cary-Blair transport medium and frozen, and the remaining whole stool was refrigerated.
Twenty samples of whole stool and corresponding Cary-Blair tubes were transported in a cooler, on ice, to
CDC for analysis. Whole stools were analyzed using electron microscopy and reverse transcriptase
polymerase chain reaction. Bacterial specimens were examined for pathogens including the following:
Salmonella spp., Shigella spp., Vibrio spp., Campylobacter spp., E.coli O157:H7, Yersina entercolitica,
Bacillus cereus, Staphylococcus aureus, and enterotoxigenic E. coli. Selected samples were tested for
Norwalk-like virus using RT-PCR with a region “B” primer set.
- Samples from cooked baby scallops, cooked baby shrimp and scallop salad, and pre-cooked jumbo shrimp
from the galley cold pantry refrigerators were examined at the VSP lab for bacterial content by total
plate count for total coliforms, E. coli, S. aureus, Salmonella spp., and fecal coliforms.
- Environmental Investigation/Sanitation Inspection
- The investigative team performed an environmental health inspection of the vessel focusing on the
period from March 24, 2002 to April 3, 2002. This included inspection of housekeeping, food safety
procedures, and testing of potable water systems. Temperature logs were reviewed for all food refrigerator
units; the ship records of the free residual chlorine concentration in the potable water tanks and
distribution system were also reviewed. The executive chef and food and beverage manager were interviewed
about food service. The ship’s Captain, Staff Captain, and Deck Engineer were interviewed about the
potable water system and bunkering of water. The medical staffs were interviewed about recent
gastrointestinal illness in the crew. Water samples were collected from potable water tanks, distribution
points, and ice machines and analyzed for the presence of bacteria using standard methods for membrane
filtration and most probable numbers. Tests were performed looking at total plate count and total and
fecal coliforms.
Results
- Epidemiologic Investigation
- Descriptive epidemiology
- Completed questionnaires were returned by 431 (69%) of 621 passengers and by 340 (86%) of 395
crew. Of passenger respondents, 225 (53%) reported having had symptoms that met the case definition of
gastroenteritis; 41 (9%) had indeterminate illness and were excluded from further analysis; 23 passengers
met the secondary case definition and were excluded from the analysis; 165 (38%) were well. The median age
of ill passengers was 66 years (range 13 – 89 years); 56% were female. Well passengers did not differ in
age and sex from ill passengers. Illness among passengers and crew was characterized by primarily
diarrhea with accompanying abdominal cramps, nausea, and headache (Table 1). Vomiting was reported by 70
(41%) and fever in 41 (25%). For passengers who had recovered, the median duration of illness was 3 days
(range 1 – 9 days); 30% (66/221) reported being ill at the time they returned their questionnaires on day
11 or 12 of the cruise. Of passengers who met the primary case definition, 50% of ill passengers
reported onset of gastroenteritis within the first five days of the cruise (Figure 1). The peak date of
illness onset for passengers was March 28, 2002, which was the 5th day of the cruise.
- Cohort Study
- Potable water and ice were considered possible vehicles of transmission of disease given the
large number of ill passengers with onset of illness spread over many days. Higher gastroenteritis attack
rates were observed among passengers who had consumed any beverages with ice before they became ill
compared with passengers who had not (Table 2); 185 (58%) of 317 passengers consumed beverages with ice
before they became ill, compared with 17 (33%) of 51 passengers who had not consumed any beverages with
ice before they became ill [relative risk (RR) = 1.75, 95% CI = 1.17 – 2.61]. In addition, dose-response
effects were noted among passengers, with increased consumption of beverages with ice associated with
increased attack rates of gastroenteritis (chi-square test for trend = 8.31, p <0.005). There were no
differences between gastroenteritis attack rates when comparing passengers who had or had not consumed any
unbottled (ship’s potable) water during the cruise (RR = 1.10, CI = 0.73 – 1.67). There were only 2
passengers who drank only bottled water during the study period. There were no significant differences in
gastroenteritis attack rates among passengers who went on shore excursions compared with those who did
not (Table 2). Shore excursions were not associated with passenger illness. Similarly, eating meals on
specific days, eating specific meals, or eating specific food items were not associated with passenger
illness.
- Gastroenteritis attack rates were also higher among crew members who had consumed any beverages with
ice compared with crew members who had not; 18 (19%) of 196 crew members who consumed any beverages with
ice became ill, compared with 6 (4%) of 141 crew members who had not consumed any beverages with ice
(RR = 2.13, CI = 0.87 – 5.23).
- Laboratory Investigation
- Whole stool samples were collected from 14 passengers and 6 crew; 2 swabs for bacterial analysis were
obtained from each of the whole stool specimens. Three specimens exhibited no growth. Enterotoxigenic E.
coli (ETEC) was isolated from eight passengers and one crew member (Table 3). Multiple ETEC serotypes
were isolated: O27:H7 (5), O148:H28 (2), O79: Hund (1), O25:NM (1), O6:H16 (1). All of the serotypes had
the gene sequence for the heat-stable toxin (ST) and two had gene sequences for both the heat-stable toxin
and the heat-labile toxin (LT/ST). Shigella sonnei was also isolated from one passenger. All 20 cultures
were negative for Salmonella, Yersinia, Campylobacter, E. coli O157:H7, and Vibrio species.
- Ten stool samples, five that were positive for ETEC, from seven passengers and three crew, tested
negative for Norwalk-like virus.
- Environmental Investigation
- Record review and food service inspection with the Food and Beverage Manager and Executive Chef
revealed hot/cold food storage temperatures and preparation practices in compliance with VSP sanitation
requirements. Food handlers wore disposable gloves and aprons as required.
- During the cruise, water was bunkered (potable water taken on in port) in Acapulco (on 3/24),
Guatemala (3/26), Costa Rica (3/28), Panama (3/30), and Jamaica (4/3). On the M/V Caronia, bunkered water
is routinely tested for the presence of total coliforms and E. coli using Colilert test kits before and
immediately after chlorine injection. The water bunkered in Guatemala tested positive for total coliforms
and E. coli pre-chlorination and tested positive for total coliforms and negative for E. coli post-
chlorination. No further treatment was administered prior to distribution. From potable water chlorine
analyzer records, potable water chlorine levels were observed to be appropriate (between 0.5 – 2.0 ppm) at
the distribution system level during the entire cruise, never dropping below the 0.2 ppm minimum
requirement. Chlorine was added to the bunkered water at the required 2 mg/L. This was increased to 3
mg/L after the positive test from the water bunkered in Guatemala.
- Ice machines delivered ice in a manner where ice handling was not considered to contribute to
contamination. There was however, one ice machine on the lido deck buffet where the trigger contacted the
lip contact surface for the cups. A sign posted advised passengers not to refill used cups, but
passengers were observed re-using cups. Activated charcoal filters were in place on all ice machines to
remove chlorine from water before it was frozen into ice. Samples of water (n = 9) and ice (n = 4) taken
from the ship on April 5, 2002 and tested by VSP tested negative for the presence of coliforms.
- Discussion
- A large outbreak of gastroenteritis caused by ETEC occurred among passengers and crew aboard the
M/V Caronia during a cruise from Acapulco, Mexico on March 24, 2002 to Fort Lauderdale, Florida on April
5, 2002. Clinical characteristics of illness were consistent with ETEC, which was identified among 9 of
20 stool samples collected from ill passengers and crew. The peak of the outbreak occurred on the fifth
day of the cruise. Given that the typical incubation period for ETEC infection is between 21-48 hours,
the initial exposure most likely occurred in the first several days after embarkation. Questionnaire data
revealed a statistical association between consumption of beverages with ice and illness among passengers
and a dose response related to the number of iced beverages consumed. A similar association was seen
among the crew members, although it was not statistically significant probably because of the small number
of cases among the crew.
- The shape of the epidemic curve (Figure 1) is most likely due to several factors. In this case,
contaminated water contained multiple pathogens resulting in several distinct incubation periods which are
represented in the shape of the epidemic curve. Furthermore, the ship offered free health visits for
anyone with diarrhea beginning on March 31 which explains a rise in case numbers identified.
- The most likely source of contamination of the ice was the water used in the ice makers. Based on the
onset dates, this could have been water bunkered in Acapulco or Guatemala. Findings from the environmental
investigation demonstrated that the potable water bunkered in Guatemala was contaminated with coliforms
before and after chlorination. This suggests that water was contaminated with enough fecal material to
survive standard chlorination and allowed ETEC to be introduced into the ship’s water system.
Furthermore, the multiple serotypes of ETEC found in stool samples from ill passengers and crew support
the finding that there was fecal contamination of the bunkered water.
- Epidemiologically, ice was associated with illness, but not the ship’s water. One hypothesis
accounting for this is that ETEC reached the ice machines through the water in conditions of inadequate
chlorination. There, the filters removed chlorine prior to freezing. ETEC could then have remained viable
in the non-chlorinated ice. The same water may have had longer chlorine contact time in the potable water
system allowing for better disinfection. The fact that ice and water samples taken by VSP were negative
for the presence of coliforms at the time of the investigation is not surprising given the additional
chlorine added to the water system upon identification of the outbreak. It is unlikely that ice was
contaminated by ice handling, given that ice machines used on board the ship had separate dispensers and
trigger buttons.
Recommendations
- On April 12, 2002, VSP made the following recommendations to Cunard Line Limited for immediate
implementation:
- I. General recommendations for the control of gastroenteritis aboard the next cruise:
- 1. Continue to submit daily reports of all diarrheal illness over the next several cruises to
monitor for cases of gastroenteritis.
- 2. Encourage both passengers and crew with diarrhea to immediately report illness to the infirmary.
Obtain and label stool samples from all passengers and crew who have diarrhea and refrigerate immediately.
- 3. Reinforce the importance of good hand washing practices among all crew.
- 4. Exclude food handlers with vomiting or diarrhea or a history of vomiting or diarrhea until they are
symptom-free for 72 hours before returning to duty. Cabin mates of sick crew should be confined to cabins.
If they experience no illness after 48 hours they can return to work.
- 5. Establish procedures for handling soiled crew cabin laundry separately, as is the case for soiled
passenger laundry. A separate machine should be used with high heat and chlorine added.
- II. Specific recommendations for management of potable water on the M/V Caronia:
- 1. Bunker water only from reliable sources of well documented quality. Specifically avoid bunkering in
Guatemala on future cruises.
- 2. Increase free chlorine residual to 3 ppm or greater when bunkering potable water.
- 3. Maintain free chlorine residual at 1 ppm at the far point of the distribution system during the
next cruise.
- 4. Monitor and record the tanks filled during bunkering and record a quantity in tons for each tank.
- 5. Conduct microbiological tests on all potable water being bunkered. Water that is positive should be
stored and the free chlorine levels should be raised to 5 ppm and the tanks retested after chlorination.
If water is still positive after initial chlorination, water should be held for 24 hours and retested. No
water should be distributed that is still positive. If possible, any water testing positive should be
dumped.
- 6. Empty all ice machines, clean, sanitize, and make new ice.
- 7. Eliminate passenger self-service in the lido buffet by posting staff to serve passengers food from
the serving line and drinks from the beverage station. Repair or replace the ice maker/dispenser so the
trigger is separate.
- 8. Thoroughly disinfect all passenger garbage receptacles and sanitize ice buckets. Use disposable
plastic liners in ice buckets and trashcans in all cabins.
Acknowledgements
- Cunard Line Limited, staff and crew of the M/V Caronia cooperated fully with this investigation. They
facilitated distribution and collection of passenger and crew surveys, collection and storage of stool
samples, provided copies of updated environmental and medical records, and implemented recommendations
listed above.
- Tom M. Chiller MD,MPH
- Epidemic intelligence Service Officer
- Foodborne and Diarrheal Diseases Branch
- Division of Bacterial and Mycotic Diseases
- National Center for Infectious Diseases
- Elaine H. Cramer, MD,MPH
- Medical Epidemiologist
- Vessel Sanitation Program
- Division of Emergency and Environmental Health Services
- National Center for Environmental Health
Appendix
- Table 1 Characteristics of clinical illness (from 225 ill passengers and 24 ill crew members), MV
Caronia cruise, March 24- April 5, 2002.
- Table 2 Gastroenteritis attack rates among passengers associated with exposure to selected risk
factors, MV Caronia cruise, March 25 – April 5, 2002.
- Table 3 Stool specimen ( n = 10) results from passengers and crew members with gastroenteritis aboard
the MV Caronia cruise, March 24 – April 5, 2002.
- Figure 1 - Date of illness onset among passengers aboard the MV Caronia cruise, March 24 – April 5,
2002