Investigation of Gastroenteritis aboard Palm Beach Princess
CDC's Investigation of Gastroenteritis Aboard Palm Beach Princess, May 18-19, 2000
Background
- 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.
- Objectives
- 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.
Methods
- Case Definition
- 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.
- Passenger Survey
- 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.
- Epidemiologic Investigation
- Descriptive Epidemiology
- 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).
- Cohort Study
- 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.
- Environmental Investigation
- 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.
- Discussion
- 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.
Recommendations and Follow-up Activities
- As a result of this foodborne outbreak, and after reviewing food preparation and handling
practices on the ship, VSP made the following recommendations:
- General
- 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.
- Galley
- 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
Table 1 Characterization of illness (n=51) for passengers with gastroenteritis, Palm Beach
Princess cruise ship, May 18, 2000
Symptom |
Ill Passengers (%) |
Diarrhea |
41 (80) |
Vomiting |
7 (14) |
Nausea |
24 (47) |
Abdominal Cramps |
38 (75) |
Fever |
3 (6) |
Muscle Aches |
7 (14) |
Bloody Stool |
3 (6) |