An explosive outbreak of gastroenteritis caused by a parvovirus-like (PVL) agent (Norwalk agent) affected 521 (64%) cruise ship passengers in 1977. The illness was characterized as mild-to-moderate and lasted one to two days. Principal symptoms experienced by ill passengers were nausea, vomiting, and diarrhea; fever was reported for approximately 25% of the patients. The outbreak was compatible with a common-source exposure, but no such exposure was identified. On the next four cruises, passengers experienced a similar gastrointestinal illness, but the outbreaks were less explosive, affected fewer persons, and symptoms appeared milder, on each subsequent cruise. No common source was identified, and person-to-person transmission may have occurred. The etiology of these outbreaks would have remained unknown were it not for the recent development of a specific radioimmunoassay (RIA) for the serologic identification of Norwalk virus and the measurement of antibody titers to the virus. A fourfold or greater rise in serum antibody titers to Norwalk antigen in serum from seven of eight ill passengers and the identification of Norwalk antigen in stool specimens from two ill passengers on the first cruise demonstrated that Norwalk virus caused this outbreak. The symptoms experienced by passengers on the four subsequent cruises suggest that a Norwalk agent probably also caused these outbreaks. In addition, a stool specimen from an ill passenger on cruise 3 contained Norwalk antigen.

An invasive strain of Escherichia coli (ONT:NM) was isolated from stool specimens from 7 of 10 ill passengers who developed diarrhea during a 5-day ocean cruise. The ill passengers had shared no common exposures off the ship before or during the cruise. Three of the persons whose stools were cultured were part of a tour group of 219 persons, and a food consumption and health history questionnaire was completed by 190 members (87%) of this tour group. Forty-seven (25%) had had diarrhea during the cruise; other symptoms among those with diarrhea included nausea (72%), abdominal cramps (68%), headache (68%), chills (60%), dizziness (53%), myalgias (43%), subjective fever (36%), and vomiting (26%). The median duration of symptoms was 3 days. Eating at cold buffets on ship and eating potato salad, a buffet food item, were significantly associated with illness. No evidence of secondary spread of illness in household contacts of the ill person was found.

SUMMARYWe reviewed data from the Vessel Sanitation Program (VSP), established by the US Public Health Service in 1975, to describe the epidemiology of shipboard diarrhoeal outbreaks, determine the risk of outbreak-related illness among cruise ship passengers, and evaluate changes in rates and patterns of shipboard diarrhoeal illness since the VSP was implemented. When the programme began, none of the cruise ships passed periodic VSP sanitation inspections; since 1978, more than 50 % of ships have met the standard each year.

Outbreaks of illness on passenger cruise vessels during 1970–1975 were caused by Shigella flexneri, Salmonella, and Vibrio parahaemolyticus. Vehicles for the etiological agents were water, multiple foods, seafood cocktail, and shrimp and lobster. Staphylococcus aureus caused two outbreaks of foodborne illness on aircraft during the same period. Vehicles were custard and ham.