Diarrheal disease on cruise ships, 1990-2000: the impact of environmental health programs.

Background: In 1975, the then-Center for Disease Control (CDC) established the Vessel Sanitation Program (VSP) to minimize the risk for diarrheal disease among passengers and crew aboard ships by assisting the cruise ship industry in developing and implementing comprehensive environmental health programs.

Objectives: To evaluate the relationship between cruise ship sanitation scores and diarrheal disease incidence and outbreaks among cruise ship passengers.

Methods: Retrospective cohort study of ship inspection and diarrheal disease data from 1990 through 2000 from the National Center for Environmental Health, CDC database, for cruise ships entering the United States.

Outcomes: Yearly trends in number of ships inspected, number of inspections conducted, inspection scores, and risks of failing inspections; rates of diarrheal disease among passengers, by inspection year, cruise duration, incidence of outbreaks, and passing- or failing-score status of the associated ship.

Results: From 1990 through 2000, inspection scores gradually increased from a median of 89 in 1990 to 93 in 2000 (p<0.001), with an associated statistically significant 21% increase in likelihood of passing. The total baseline level of diarrhea among passengers was 2.0 cases per cruise (13243/6485), or 23.6 cases per 100,000 passenger-days (13243/56129096). The latter rate declined significantly from 29.2 in 1990 to 16.3 in 2000 (p<0.0001). Diarrheal disease incidence rates among passengers sailing on ships that passed environmental inspections were significantly lower than rates among passengers sailing on ships that failed inspections (21.7 vs 30.1; RR = 1.39; 95% CI: 1.31-1.47). Diarrheal disease outbreak-related illnesses decreased from 4.2 to 3.5 per 100000 passenger-days from 1990-1995 to 1996-2000.

Conclusions: Environmental sanitation inspections conducted among ships sailing into the United States appear to continue to decrease diarrheal disease rates and outbreaks among passengers.