Current Trends Vessel Sanitation Scores

The Centers for Disease Control (CDC) established the Vessel Sanitation Program in 1975 as a cooperative activity with the cruise ship industry. The goals of the program were to achieve and maintain a level of sanitation on passenger vessels that would lower the risk of gastrointestinal disease outbreaks and provide a healthy environment.

To meet these goals, CDC began inspecting all passenger cruise ships that had foreign itineraries and arrived at ports under U.S. control. Between 1975 and 1985, CDC conducted three types of inspections: semiannual, follow-up, and "other." All inspections were unannounced and were conducted upon a ship's arrival in port. Inspectors rated cruise ships on water quality, food preparation and handling, potential for contamination of food, general cleanliness, methods of food storage, and repair of food service equipment. If a vessel failed a semiannual inspection, CDC conducted one or more follow-up inspections, depending on the itinerary of the cruise ship. "Other" inspections were conducted for special purposes, such as investigating a specific item (e.g., shipboard water chlorination levels) or a gastrointestinal disease outbreak.

From the program's inception through 1985, CDC conducted nearly 1,800 inspections of 172 vessels. In the first months of the program, ships received a simple pass or fail rating. Beginning in late 1975, however, CDC assigned a numerical score based on the same detailed criteria. Scores ranged from 1 to 100 points; 86 or above was considered satisfactory. The data collected during these inspections indicate major changes since 1975: the number of cruises per year and the number of passenger days per year have increased, while the number of diarrheal disease outbreaks per 10 million passenger days has decreased (Figure 1).

To assess the effectiveness of the Vessel Sanitation Program, CDC reviewed inspection data from 905 semiannual inspections performed from 1975-1985. The semiannual inspections are thought to best represent shipboard conditions because they were all complete inspections. Some inspections during the early years, although unannounced and rated, were not complete.

A cruise ship was considered to have experienced an outbreak if at least 3% of passengers or crew sought medical attention for diarrhea from the ship's physician and if CDC was notified and initiated an investigation. Cruises with fewer than 100 passengers and cruises of less than 3 days or more than 15 days were excluded, as were cruises with diarrheal outbreaks associated with a meal eaten on shore. Two or more outbreaks on consecutive cruises of the same vessel were considered to be a single outbreak unless they were known to be of different etiologies. During the period 1975-1985, CDC investigated 45 such shipboard outbreaks.

For the purpose of analysis, CDC ranked ships on the basis of their average inspection scores and their percentage of satisfactory inspections. To determine the percentage of satisfactory inspections, all numerical scores during the 10 years were converted to a satisfactory or unsatisfactory rating. This conversion allowed for the inclusion of data from the beginning of the program. The ranking was then divided into three groups: the upper 20%, the middle 60%, and the lower 20%. To determine the total passenger days for each ship, the number of passengers on board qualifying cruises was multiplied by the duration of each cruise (e.g., a 5-day cruise with 200 passengers had 1,000 passenger days). Rates per 10 million passenger days were then calculated for: 1) the number of ships with one or more outbreaks in each group and 2) the total number of outbreaks per passenger days for each group.

The analysis based on average scores alone revealed that, for every 10 million passenger days, 1.8 ships in the upper 20%, 3.5 ships in the middle 60%, and 8.1 ships in the lower 20% had one or more diarrheal outbreaks (Table 1). The results of the analysis based on the satisfactory/unsatisfactory rating system were similar. A comparable analysis of shipping lines (companies that own passenger vessels) demonstrates the same association between lower inspection every 10 million passenger days, 1.8 ships in the upper 20%, 3.5 ships in the middle 60%, and 8.1 ships in the lower 20% had one or more diarrheal outbreaks (Table 1). The results of the analysis based on the satisfactory/unsatisfactory rating system were similar. A comparable analysis of shipping lines (companies that own passenger vessels) demonstrates the same association between lower inspection scores and increasing rates of diarrheal disease outbreaks.

Since some ships had multiple disease outbreaks during the 10-year study period, the number of outbreaks per 10 million passenger days in each of the three ranking groups were analyzed (Table 2). This analysis, which was based on average scores and, thus, excluded the early "failing" ratings, showed that the likelihood of outbreaks increased with decreasing inspection scores. Reported by: Special Programs Group, Office of the Director, Center for Environmental Health and Injury Control, CDC. Editorial Note:

Shipboard sanitation is a significant factor in preventing diarrheal disease outbreaks on cruise ships (1). The occurrence of several major disease outbreaks on these vessels prompted CDC to initiate the Vessel Sanitation Program in the early 1970s. The program operated continuously at all major U.S. ports until 1986, when CDC terminated portions of the program. However, a restructured program became operational on March 1, 1987. Effective March 1, 1988, the Vessel Sanitation Program will be funded by user fees, which will reimburse the government for program costs.

A review of data from the Vessel Sanitation Program indicates that ships that consistently have the highest sanitation scores are less likely to have an outbreak of diarrheal disease than ships with lower average scores. The only analysis showing a slightly different trend was based on the percentage of satisfactory scores for individual ships. In this analysis, the middle ranking group appeared to experience a higher number of outbreaks than the lower ranking group, but both groups had more outbreaks than the highest ranking group. There are several possible explanations for this different pattern, but it is likely to be due either to the small numbers involved or to incomplete surveillance.

While this report is based on the best available information, it is important to remember that vessel sanitation inspections are not designed simply to prevent diarrheal illness and that the data collected can give only a crude estimate of the inspection program's impact on epidemic diarrheal disease. Nevertheless, the data consistently demonstrate that the cooperative effort between the cruise ship industry and CDC has helped to prevent outbreaks of diarrhea on cruise ships. The data collection system for the Vessel Sanitation Program has been revised and will allow for more precise analysis in the future.

References

1. Dannenberg AL, Yashuk JC, Feldman RA. Gastrointestinal illness on passenger cruise ships, 1975-1978. Am J Public Health 1982;72:484-8.

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