Trichinellosis surveillance--United States, 1997-2001

Trichinellosis is a parasitic disease caused by tissue-dwelling roundworms of the species Trichinella spiralis. The organism is acquired by eating Trichinella-infected meat products. The disease has variable clinical manifestations, ranging from asymptomatic to fatal. In the United States, trichinellosis has caused hundreds of preventable cases of illness and occasional deaths. The national trichinellosis surveillance system has documented a steady decline in the reported incidence of this disease, as well as a change in its epidemiology.

This report summarizes surveillance data for trichinellosis in the United States for 1997-2001.

Trichinellosis became a nationally reportable disease in 1966, but statistics have been kept on the disease since 1947. The national trichinellosis surveillance system is a passive system that relies on existing resources at the local, state, and federal levels. Cases are diagnosed based on clinical history with laboratory confirmation. Cases are reported weekly to CDC through the National Electronic Telecommunications System for Surveillance (NETSS). Detailed data regarding signs and symptoms, diagnostic tests, and food consumption are gathered by using a supplementary standardized surveillance form and are reported to CDC by fax or mail. This information is compared with NETSS data several times a year by CDC staff. Discrepancies are reviewed with the state health departments. The purpose of the surveillance system is to determine the incidence of trichinellosis, to maintain awareness of the disease, to monitor epidemiologic changes, to identify outbreaks, to guide prevention efforts, and to measure the effectiveness of those efforts.

Although trichinellosis was associated historically with eating Trichinella-infected pork from domesticated sources, wild game meat was the most common source of infection during 1997-2001. During this 5-year period, 72 cases were reported to CDC. Of these, 31 (43%) cases were associated with eating wild game: 29 with bear meat, one with cougar meat, and one with wild boar meat. In comparison, only 12 (17%) cases were associated with eating commercial pork products, including four cases traced to a foreign source. Nine (13%) cases were associated with eating noncommercial pork from home-raised or direct-from-farm swine where U.S. commercial pork production industry standards and Regulations do not apply.

The majority of the decline in reported trichinellosis cases is a result of improved observance of standards and regulations in the U.S. commercial pork industry, which has altered animal husbandry practices resulting in reduced Trichinella prevalence among swine.

Because of the change in epidemiology of trichinellosis and the continued occurrence of cases among consumers of wild game meat and noncommercial pork, more targeted public education is needed to further reduce the incidence of this disease.