Epidemiology of diarrheal disease outbreaks on cruise ships, 1986 through 1993

To describe the epidemiology of cruise-associated diarrheal disease outbreaks from 1986 through 1993, to determine if the incidence had changed since 1985, and to determine the preventability of outbreaks that continue to occur.

The numerator data were collated from Centers for Disease Control and Prevention (CDC) outbreak investigation reports from 1986 through 1993. The denominator data were summations of cruise ship data on the number of passengers and length of cruises collected during routine diarrheal illness surveillance, available only for the period 1989 through 1993.

Cruise ships with outbreaks of diarrheal disease.

Cruise ship passengers and crew of staff ho participated in the original investigations.

The incidence of outbreaks during the study period, pathogens isolated, and vehicles of transmission implicated in investigations.

Among cruises of 3 to 15 days, CDC staff investigated 1.4 outbreaks per 1000 cruises, or 2.3 outbreaks per 10 million passenger-days. An etiologic agent was implicated in 21 (68%) of 31 investigated outbreaks: bacterial in 12, viral in nine. A specific vehicle of transmission was identified in 16. The most common vehicles of transmission were undercooked scallops (three outbreaks caused by enterotoxigenic Escherichia coli), eggs (two outbreaks caused by Salmonella serotype Enteritidis, one by Norwalk-like virus), and food items provided by caterers during onshore excursions (three outbreaks, one caused by Shigella sonnei).

Observance of two simple precautions could have prevented almost one third (5/16, or 31%) of the investigated outbreaks on cruise ships. Cruise lines have been reminded to cook seafoods thoroughly and to use pasteurized eggs for menu items calling for pooled eggs. Preventing food handlers from working while ill and not using onshore caterers for offship excursions might have prevented at least an additional one third (5/16) of these outbreaks.