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Sanitation - Continued

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 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

TABLE 1. Number of cruise ships and shipping lines with at least one diarrheal disease outbreak per 10 million passenger days, by ranking groups* Vessel Sanitation Program, 1975-1985

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*Investigators ranked ships on the basis of their inspection scores and divided the ranking into three groups for analysis.

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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.

TABLE 2. Number of diarrheal disease outbreaks per 10 million passenger days, by ranking groups* Vessel Sanitation Program, 1975-1985

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*Investigators ranked ships on the basis of their inspection scores and divided the ranking into three groups for analysis.

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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The following are indicators of influenza activity in the United States for the weeks ending January 30 and February 6, 13, and 20. Numbers and percentages are provisional and may change as additional reports are received for the given weeks.

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*Sporadically occurring cases, no known outbreaks.

*Outbreaks in counties in which total population comprises less than 50% of total state population.

$Outbreaks in counties in which total population comprises 50% or more of total state population.

Members of the American Academy of Family Physicians who submit weekly influenza surveillance reports based on their patient population.

**States without confirmed influenza A(H3N2) to date: Kentucky, Maine, Massachusetts, Nevada, New Hampshire, New Jersey, North Carolina, Rhode Island, Vermont, and Virginia. **States reporting isolates of influenza A(H1N1) to date: Arkansas, Georgia, Maryland, New York, and Texas. The isolate from Texas resembles influenza A Taiwan/1/85 (H1N1). $$ States reporting isolates of influenza B to date: Alabama, Arizona, California, Hawaii, Michigan, Montana, Nevada, New York, Ohio, Tennessee, Virginia, Washington, and Wisconsin.

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The Morbidity and Mortality Weekly Report is prepared by the Centers for Disease Control, Atlanta, Georgia, and available on a paid subscription basis from the Superintendent of Documents, U.S. Government Printing Office, Washington, D.C. 20402, (202) 783-3238.

The data in this report are provisional, based on weekly reports to CDC by state health departments. The reporting week concludes at close of business on Friday; compiled data on a national basis are officially released to the public on the succeeding Friday. The editor welcomes accounts of interesting cases, outbreaks, environmental hazards, or other public health problems of current interest to health officials. Such reports and any other matters pertaining to editorial or other textual considerations should be addressed to: Editor, Morbidity and Mortality Weekly Report, Centers for Disease Control, Atlanta, Georgia 30333.

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