Outbreak of GI Illness Aboard the Cruise Ship, M/V Nantucket Clipper

Background
On January 20, 200zero, New World Ship Management Company notified the Vessel Sanitation Program (VSP), National Center for Environmental Health (NCEH), Centers for Disease Management and Prevention (CDC), that ten of eighty five passengers, and 9 of thirty five crew aboard the M/V Nantucket Clipper had reported to the ship’s captain with diarrhea or vomiting. The ship had taken on passengers five days earlier in St. Thomas, U.S. Virgin Islands. At the time of the report, the ship was sailing in the British Virgin Islands. The primary cases were documented by the captain on Wednesday, January nineteenth, the fourth day of a seven-day cruise. VSP workers recommended public health interventions and heightened surveillance activities to the ship management company for immediate implementation.
On January 25, 2000, the Vice President of New World Ship Management Company notified VSP that fourteen of ninety seven passengers, and three of thirty five crew aboard the second cruise of the M/V Nantucket Clipper had reported to the Captain or crew with diarrhea or vomiting. By January twenty six, 200zero, the sixth day of the cruise, nineteen passengers and five crew were unwell, for a combined attack rate of 18p.c (Table one).
On the premise of the continued incidence of diarrheal illness among passengers and crew throughout the second in an exceedingly series of 7-day cruises aboard the M/V Nantucket Clipper, VSP initiated an epidemiologic and environmental investigation. VSP workers flew to St. Thomas Virgin Islands to board the vessel on January twenty nine, 2000 in St. Thomas, U.S. Virgin Islands, the primary US port of the vessel’s itinerary when it set sail on January 23, 2000.

Objectives
The objectives of the investigation were to; one) determine the etiologic agent associated with the outbreak; two) confirm the supply(s) of unfold of illness among passengers and crew; 3) formulate interventional methods to manage the outbreak and stop a recurrence.
Ways
Epidemiologic Investigation
Case Definition
A case of gastroenteritis was defined as diarrhea (three or a lot of loose stools during a twenty four-hour period) or vomiting in an exceedingly passenger or crew member aboard the M/V Nantucket Clipper with onset on or once January 23, 2000.
Food Menus and Passenger Activities
Ship menus were obtained from New World Ship Management for the M/V Nantucket Clipper throughout the week January twenty three-thirty,200zero. VSP employees interviewed the corporate by phonephone to review food preparation and handling practices and to match things listed on menus with food-production records. VSP workers conjointly reviewed, by phone, water and ice handling practices with daily passenger and crew activities. The chef and hotel manager were subsequently interviewed head to head once members of the investigative team were aboard the ship.
Passenger Survey
A standardized questionnaire, based on ship menus, food-preparation practices, and daily activities was administered to all passengers and crew on the morning of January 29, 200zero. Questionnaires were administered in person by VSP’s employees epidemiologist and therefore the environmental health officer. Interviewees were asked concerning demographic info, and risk factors for illness (e.g. shore excursions, food and water consumed), and were asked to pick, from a list of food things, the foods they ate throughout of the cruise. The questionnaires were used to characterize passenger demographics, timing of illness, attack rates, symptomatology, and risk factors for illness.
Case Interviews
Several case-patients among passengers and every one case-patients among crew members were interviewed in-person to review exposure histories and determine individual risk factors for acquiring gastroenteritis prior to the onset of illness.
Records Review
VSP employees reviewed the ship’s medical log for data regarding gastrointestinal symptoms among passengers and crew throughout the cruise and to verify attack rates. As a result of of the little size of the vessel and therefore the absence of medical workers, the log was maintained by the Captain and Initial Officer of the M/V Nantucket Clipper.
Statistical Ways
Analysis of disease onset was based on came questionnaires from each ill passengers and crew members. People who reported symptoms but whose illness failed to meet the case definition were excluded from the cohort study. Descriptive and cohort analyses were based mostly on the whole passenger and crew data set.
Information from questionnaires were entered and analyzed using Epi Information version vi.02 software. Baseline characteristics of ill and well passengers and crew (e.g. symptomatology; and water, food, and ice consumption) were described by frequencies and percentiles for categorical variables (e.g., number of folks with diarrhea), and ranges of values for continuous variables (e.g., age). Exposure variables were coded as dichotomous variables. In univariate analysis, risk ratios with ninety five% confidence intervals were used to test for variations in illness risk between unwell and well individuals. Covariates identified as important in univariate analyses were included in multivariate regression models.
Multivariate analyses were performed using SAS version half dozen.twelve software, by using multiple logistic regression to judge the freelance association of risk factors with gastrointestinal illness. A model was derived to best characterize the probability of gastrointestinal illness whereas controlling for different potential risk factors. To acquire a reduced model that best characterised the probability of illness, a sequential, forward-stepwise elimination procedure was performed. Confounding variables were retained in the model if the beta coefficient for exposure was modified by > 10percent.
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Laboratory Investigation
On January 30, 2000, VSP employees collected serum and stool samples from ill passengers and crew members for bacterial and viral testing. Whole stools were transported in specimen cups to CDC and were tested for tiny round structured virus (SRSV) using electron microscopy (EM) and for Norwalk-like virus using polymerase chain reaction (PCR) analysis. Bacterial swabs were transported in Cary-Blair medium to CDC and examined for bacterial pathogens (Campylobacter, Salmonella, Shigella, Vibrio parahaemolyticus, toxigenic Escherichia coli, and Yersinia enterocolitica).
Environmental Investigation/Sanitation Inspection
VSP also conducted a review of housekeeping procedures that included evaluating infection-control measures, routine cabin and public house cleaning practices, laundry facilities, and sanitization of snorkeling gear. The inspection concerned a review of food storage, preparation, cleaning, and service practices within the galley and bars. The free residual chlorine concentration in the potable water holding tanks and distribution system was measured and a visual inspection and record review was performed to identify attainable direct or indirect cross-connections between potable and non-potable water stores.
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Results
Epidemiologic Investigation
Descriptive epidemiology
Completed questionnaires were came by 93 (ninety six%) of ninety seven passengers and by 34 (ninety sevenp.c) of thirty five crew. Of respondents, seventy seven (eighty threepercent) of passengers and 21 (sixty two%) of crew members reported having had symptom(s) that met the case definition of gastroenteritis. Diarrhea was reported in 80 (82p.c) of cases, vomiting in sixty eight (70%), nausea in sixty one (sixty threepercent), muscle aches in 42 (43%), bloody stools in 2 (two%), headache in 38 (thirty-ninep.c) abdominal cramps in thirty six (37p.c), and fever in 36 (37percent;[Table two]). The duration of illness was a pair of days or less for fifty nine (71p.c) of the cases, the onset of illness peaked on the third day of the cruise. The median age of sick passengers was 65 years (vary 10-72 years); the median age of unwell crew members was 24 years (range twenty one-seventy two years); 49 (fiftyp.c) of all case subjects were female.
Cohort study
In an unadjusted analysis, persons who used the ice bucket in their cabins, obtained ice from the most lounge, ate the breakfast served on January 24, 2000, and who consumed bread served at breakfast on January twenty four, 200zero, were a lot of seemingly to become sick with gastroenteritis (Table 3). When we have a tendency to adjusted by multiple logistic regression for risk factors determined statistically vital by univariate analysis, we found that solely consuming breakfast on January twenty four, 2000 was statistically important, (OR = three.nine, CI: one.fifty,10.31).
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Laboratory Investigation
5 of eight recent stool specimens were postivie for SRSV by electron microscopy. Seven of eight specimens were positive for Norwalk-like virus by RT-PCR using a “region B” primer set. Bacterial swabs of specimens were negative for Shigella spp., Vibrio spp., Campylobacter jejuni, Yersinia spp., E Coli 0157: H7 and enterotoxigenic E. Coli.
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Environmental Investigation
Record keeping aboard the ship was sensible. The ship’s medical log accurately reflected numbers of unwell passengers and crew. From potable-water chlorine analyzer records, we have a tendency to determined potable water chlorine levels were applicable (between one.zero and three.zero ppm) at the distribution-system level during the entire cruise, never dropping below the zero.2 ppm minimum demand. Analysis of samples collected and tested by VSP from the potable water distribution system revealed high chlorine concentrations in the potable water holding tanks and distribution system and no evidence of coliforms or E. coli bacteria.
There were good procedures in place for cabin cleaning, public space (surface) cleaning, and laundry practices. The galley facility had important space limitations, which created problems with proper separation of dirty and clean activities, correct and frequent handwashing, area for proper cleaning around equipment, and a good operational flow through the area. The single, two-stage ice machine was constructed during a approach that allowed debris and mould to collect on surfaces directly higher than the waterfall thus that contact with water and ice was a strong probability. This machine interior was extremely tough to wash properly because of its style. The ice machine has since been replaced with a replacement machine.
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Discussion
SRSV, that is usually known as Norwalk or Norwalk-like virus cause acute, self-restricted gastroenteritis characterized by diarrhea, nausea, vomiting, abdominal cramps, muscle aches and fever. The incubation amount and the average length of illness is from 24 to 48 hours. The epidemic curve for this outbreak among passengers supports a common source of exposure, with the peak onset of illness on the fourth day of the cruise for crew, and therefore the sixth day of the cruise for passengers, findings that are consistent with SRSV.
Questionnaire information revealed a statistical association between eating breakfast on January 24, 2000, sharing a cabin with an sick person, and illness for each passengers and crew. The strength of the association persisted when adjusted for multiple risk factors. No individual food things at that meal were identified as causative. Potential sources of unfold of SRSV embody consumption of contaminated food (e.g., seafood and prepared-to-eat foods like salads), water, ice, fomites, and person-to-person spread. Airborne transmission has been hypothesized but not established during this setting. As a result of illness was widely distributed among passengers and crew over the period of the cruise, modes of transmission probably involved both person-to-person spread and different unidentified modes, as well as the chance of an unidentified purpose supply of contamination. Consumption of non-bottled water and ice aboard the ship wasn’t related to gastroenteritis in this investigation.
Many factors obscured the flexibility to properly identify a single point source of contamination. 1st, the high attack rates resulted in comparatively low numbers of well passengers and crew, a state of affairs that limited statistical power. Second, it is seemingly that many passengers who reported being well at the time of the survey subsequently became sick or experienced subclinical infections that resulted in misclassification bias. Third, many crew were unwell the week before this investigation a factor which possibly contributed to person-to-person transmission and misclassification.
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Recommendations and Follow-up Activities
From January 30 to February half dozen, 200zero the vessel was voluntarily removed from service to carry out recommendations provided by VSP to New World Management for immediate implementation. The vessel came to service on February half dozen, 200zero. On Feb 10, VSP investigators visited the vessel in St. Johns U.S. Virgin Islands. Upon boarding the vessel and talking with the ship’s Captain, VSP learned that several passengers had become unwell throughout the cruise and fourteen had reported ill on the sixth day of the current cruise. VSP workers initiated an on the spot investigation of the apparent ongoing outbreak. An further twenty one cases were reported on the seventh day of the cruise and once VSP held discussions with the vessel’s management, the cruise for the week of Feb.13-20 was canceled and also the vessel was once once more taken out of service.
From February 6-thirteen, 2000, 45 of 82 (54.9%) passengers and 2 of 34 (five.9%) crew members on the cruise ship, M/V Nantucket Clipper, were unwell with acute gastroenteritis throughout a seven-day round-trip from St. Thomas, U.S. Virgin Islands. The incidence of self-reported illness peaked on Saturday, February twelve, 2000, the sixth day of the trip. The illness was characterized by diarrhea, vomiting, headache, abdominal cramps, and muscle aches lasting approximately one-two days for most people. Four stool specimens were collected from unwell passengers. Laboratory analysis confirmed the presence of Norwalk-like virus in all four specimens. Univariate analysis revealed no associated risk factors for illness.
Elaine H. Cramer, MD, MPH
Medical Epidemiologist
Vessel Sanitation Program
National Center for Environmental Health
Centers for Disease Control and Prevention