Investigation of Gastroenteritis aboard Palm Beach Princess
CDC's Investigation of Gastroenteritis Aboard Palm Beach Princess, May 18-19, 2000
- Recommendations and Follow-up Activities
On May 23, 2000, senior management representatives from the Palm Beach Casino Line notified the Vessel Sanitation Program (VSP), Division of Emergency and Environmental Health Services (DEEHS), National Center for Environmental Health (NCEH), at the Centers for Disease Control and Prevention (CDC) of approximately 20 reports of diarrhea and vomiting among passengers who sailed on the Palm Beach Princess cruise ship on May 18, 2000. The casino ship, which conducts twice-daily cruises 7 days per week, embarked approximately 300 passengers at 5:30 p.m. on May 18th at the Port of West Palm Beach, Florida, and disembarked passengers in the same port 6 hours later. A dinner buffet was served during the cruise from 5:30 to 7:30 p.m. No crew members were reported ill. No additional reports of illnesses among passengers or crew who embarked on subsequent cruises were received.
On May 25th, Kathleen Y. McDuffie, PhD, MPH (EPO, NCCDPHP/ DACH/BSB), Elaine Cramer, MD, MPH (VSP, DEEHS, NCEH), Thomas Hill, MPH (VSP, DEEHS, NCEH), and epidemiology elective student, Amy Nelson (EPO), departed for Palm Beach, Florida to investigate the outbreak of gastroenteritis. On May 26th, CDC investigators sailed on the afternoon cruise from noon to 5:30 p.m. aboard the Palm Beach Princess.
The objectives of the investigation were to:
(1) identify the etiologic agent associated with the outbreak;
(2) determine the source of the etiologic agent; and
(3) formulate intervention strategies to control the outbreak and prevent a recurrence.
A case of gastroenteritis was defined as diarrhea (three or more episodes of loose stools in a 24-hour period) or vomiting in a passenger who sailed on the Palm Beach Princess on May 18th, with onset during or after the cruise.
Food Menus and Passenger Activities
The ship’s menu for the May 18th evening buffet was provided by the Palm Beach Casino Line. VSP staff interviewed the ship’s management, staff, and chef to review food preparation and handling practices and to match items listed on the menu with food production records.
A standardized questionnaire that included food items from the ship’s menu, water and ice intake, and symptoms of illness was administered to passengers by telephone from May 27th through June 2nd by the EIS officer and elective student. Interviewees were asked to provide demographic information and to select from a list the foods they ate during the cruise. The questionnaires were used to characterize passenger demographic information, timing of illness, attack rates, symptoms, and possible risk factors for illness.
Data were entered and analyzed using Epi-Info version 6.04 software. Frequencies of clinical characteristics, risk ratios (RR), and 95% confidence intervals (CIs) were calculated. A two-sided p-value of <0.05 was considered statistically significant.
On May 26th, VSP conducted an environmental investigation of the vessel to review housekeeping procedures, food storage and preparation, and cleaning and service practices in the galley and bars. The VSP environmental health officer measured free residual chlorine concentration in the potable water holding tanks and distribution system and performed a visual inspection and record review to identify possible direct or indirect cross-connections between potable and non-potable water stores. VSP staff observed food storage, preparation, cleaning, temperature of refrigeration units, and service practices in the galley and bars, and conducted a general evaluation of facilities. Because this retrospective investigation was conducted 8 days after the outbreak, no food or stool samples were available at the time of the environmental investigation.
Of 335 passengers listed in the passenger manifest , 111 (33 %) completed the telephone survey. The median age of passengers who completed the survey was 45 years; sixty (54%) were female. Of 111 respondents, 51 (46%) reported having symptoms that met the case definition of gastroenteritis. Diarrhea was reported by 41 (80%) of ill passengers, vomiting by 7 (14%), nausea by 24 (47%), muscle aches by 7 (14%), bloody stools by 3 (6%), abdominal cramps by 38 (75%) and fever by 3 (6%) (Table 1). The duration of illness was 2 days for most of the ill passengers. The peak date of illness was May 19. Most passengers experienced initial symptoms of gastroenteritis between 1 a.m. and 5 a.m. on May 19. (Figure 1).
Unadjusted analysis revealed that 45 (66%) passengers who ate any dish made with shrimp (seafood stew or peel and eat shrimp) were 2.3 times as likely than passengers who did not eat a dish with shrimp to experience gastroenteritis (Table 2). Of the 44 passengers who ate seafood stew, 30 (69%) reported illness (Table 2). Passengers who ate seafood stew were 2.58 times as likely than those who did not eat seafood stew to report being ill. Of the 34 passengers who ate peel-and-eat shrimp, 22 (65%) were ill (Table 2). Passengers who ate the peel-and-eat shrimp were 2.31 times as likely than passengers who did not eat peel and eat shrimp to report illness. There were no statistically significant differences in gastroenteritis attack rates associated with any other meals or foods or with consumption of tap water or ice aboard the ship.
Overall, the cleanliness of the vessel was excellent at the time of inspection. Internal temperatures of stored foods, prepared foods, and foods on the buffet were within the range of safe holding temperatures during the inspection. A review of the ship’s records revealed that one refrigeration unit used as a blast chiller was documented to be operating above the safe temperature range on May 18. Logs for the refrigeration unit revealed normal operating temperatures to be have been consistently recorded as being 10 - 30 degrees F. However, on May 18, the unit was recorded as operating at 39 - 45 degrees F, which is outside the correct range for rapid cooling. An interview with the chef and other staff indicated that roast turkey and pork were found to be out-of-temperature that day, and, therefore discarded. However, lasagna chilled in the same freezer was not discarded. Also, many potentially hazardous foods were prepared for the evening buffet early in the morning and held in the oven, or bain marie or placed in the refrigeration unit and later reheated (as much as 8 hours after of preparation). Observation revealed that employees, except one person busing tables, were practicing good hand washing techniques and were wearing disposable gloves. Foods in storage, holding units, and on the buffet line were properly protected at the time of inspection.
A large outbreak of gastroenteritis associated with peel-and-eat shrimp and seafood stew served at the dinner buffet on May 18, 2000, occurred among passengers on the cruise ship Palm Beach Princess during an evening cruise that sailed round-trip from West Palm Beach, Florida. The epidemic curve among passengers, for this outbreak supports a common source of exposure, with the peak onset of illness on the day after the cruise. Questionnaire data revealed a statistical association between eating shrimp, and seafood stew from the embarkation buffet and illness among passengers. Because of the delay in receiving reports of this outbreak, food and clinical patient specimens were not available for laboratory analysis. As a result, no pathogen was implicated.
The implicated food may have been contaminated off-site at any stage of product preparation before the shrimp were loaded onto the vessel. Moreover, mishandling of shrimp by food preparation workers, including the possibility of cross-contamination of the cooked shrimp with raw shrimp, or mishandling of shrimp during thawing and subsequent cooking in preparation for blast chilling may have contributed. The method of contamination remains unidentified.
As a result of this foodborne outbreak, and after reviewing food preparation and handling practices on the ship, VSP made the following recommendations:
1. Choose several employees responsible for food preparation and handling and in other management positions to attend the VSP food service sanitation training course. This course is held at least four times per year.
2. Maintain a more detailed passenger manifest, complete with passenger names, phone numbers, and addresses. This will facilitate comprehensive follow-up in the event oft a future public health investigation.
3. Notify the VSP of cases of gastrointestinal illness when the proportion of cases among passengers or crew exceeds 2%. Because the Palm Beach Princess is a day cruiser, notify VSP of reports from passengers who have disembarked. VSP will conduct an on-board investigation after an invitation and only in the event that an outbreak clearly occurred or in cases of unusually severe illness.
4. Continue to conduct surveillance aboard the vessel by documenting cases of illness in the gastrointestinal illness log and reporting cases 24 hours before arriving at a US port from a foreign port.
5. In the future, preserve all suspicious food items if a foodborne outbreak is suspected. Laboratory analysis of implicated foods can assist in identifying causal pathogens.
6. Discontinue use of sponges for sanitizing solutions. Use cotton cloths that can be easily laundered or disposable one-use cloths.
7. Discard all potentially hazardous foods that have been out-of-temperature for longer than 4 hours. The four hour time period includes the entire cycle from food transport through cooking to service of the final product to passengers. For example, the time provisions are placed on the dock while waiting to be stored and any other time the food is not refrigerated or is not at a temperature of 45 degrees F or below or 140 degrees F or above, is considered as time out-of-temperature.
8. When preparing the seafood casserole served on the buffet, time each segment of the entire process to ensure that the out-of-temperature time is not exceeded. Internal temperatures of shrimp and scallops while being thawed and when folded into the sauce should be checked and should exceed 165 degrees F.
9. Maintain refrigerator holding temperatures of 41 degrees F or less. Internal food temperatures within refrigerators should be 45 degrees F or less. To achieve rapid cooling, blast chiller temperatures should not exceed 30 degrees F.
10. Mark normal temperature ranges on each refrigeration unit and maintain a separate log sheet on each unit. The blast chiller log should record the time that each food item was placed into and removed from the unit as well as the internal food temperature at the time of removal.
11. Ensure that all dining room staff wash hands between soiled and clean operations. When staff leave their stations to perform other tasks, they should remove gloves and place new gloves on when returning to stations.
12. Do not serve leftover foods from the buffet to crew after the buffet service is finished. We understand that this practice has already been discontinued.
Kathleen Y. McDuffie, Ph.D., MPH
Epidemic Intelligence Service Officer
Behavior Surveillance Branch
Division of Adult and Community Health
National Center for Chronic Disease and Health Promotion