Consumption of raw shellfish has long been known to be associated with individual cases and sporadic outbreaks of enteric illness. However, during 1982, outbreaks of gastroenteritis associated with eating raw shellfish reached epidemic proportions in New York State. Between May 1 and December 31, there were 103 well-documented outbreaks in which 1017 persons became ill: 813 cases were related to eating clams, and 204 to eating oysters. The most common symptoms were diarrhea, nausea, abdominal cramps, and vomiting. Incubation periods were generally 24 to 48 hours long, and the duration of illness was 24 to 48 hours. Bacteriologic analyses of stool and shellfish specimens did not reveal a causative agent. Norwalk virus was implicated as the predominant etiologic agent by clinical features of the illness and by seroconversion and the formation of IgM antibody to Norwalk virus in paired serum samples from persons in five (71 percent) of seven outbreaks in which testing was done. In addition, Norwalk virus was identified by radioimmunoassay in clam and oyster specimens from two of the outbreaks. Determining the source of the shellfish was not always possible, but northeastern coastal waters were implicated. The magnitude, persistence, and widespread nature of these outbreaks raise further questions about the safety of consuming raw shellfish.

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Foodborne disease outbreak data are collected, collated, interpreted and disseminated to improve food safety programs at all organizational levels. Part II of this series described the disease aspects of foodborne surveillance. This part (III) focuses on the food components, with collation of data to list vehicles, significant ingredients, the places where foods were mishandled, the methods of processing or preparation, and operations that contributed to outbreaks. Specific food items should be cited as vehicles, but they will have to be put into subgroups and categories for some tabular presentations. Significant ingredients are the items in combined (mixed) foods that are the likely sources of the etiologic agents. Places of mishandling include farms, dairies, aquatic and land environments where foods are harvested, processing plants, food service establishments, homes, and transportation. Multiple places may contribute to the mishandling in any outbreak. The method of processing include all sorts of processing operations. The method of preparation is classified into the following food service systems: raw unaltered foods, assembled/prepare serve, cook-serve, cook hold-hot, cook chill serve, cook chill reheat, and acidify serve. The contributory factors are situations or operations that allow contamination of foods and survival and/or proliferation of the etiologic agents in the foods. This data will provide direction for setting food safety program priorities, suggest places and operations at which regulations need to be established and enforced, and indicate educational and training needs. Definitions of the terms used in the tables are given, and the value and limitations of each set of data in the tables and in tables of related information commonly presented in foodborne disease surveillance summaries are reviewed. The data from the tables should be used to improve food safety programs, which is the subject of the next part of this series.