Trichinellosis surveillance - United States, 2002-2007

Abstract

Problem/condition: Trichinellosis is a parasitic disease caused by roundworms of the Trichinella genus. Humans are incidental hosts who become infected after ingestion of raw or undercooked meat containing encysted larvae of Trichinella spp. Common signs and symptoms of trichinellosis include eosinophilia, abdominal pain, fever, periorbital edema, and myalgia. National surveillance has documented a decline in the reported incidence of trichinellosis in the United States since 1947, the first year nationwide data were collected systematically. The decreased incidence of trichinellosis has mirrored the decrease of Trichinella in commercial pork products as a result of changes in pork industry management standards and government regulations. In addition, an overall decrease has occurred in the number of cases of trichinellosis related to pork consumption. During 1997-2001, meats other than pork were the most common source of infection, and more cases were associated with home-raised pork than with store-bought pork.

Reporting period covered: 2002-2007.

Description of system: Trichinellosis is a reportable disease in 48 states and has been a nationally notifiable disease since 1966. Cases are defined by clinical characteristics and the results of laboratory testing for evidence of Trichinella infection. States report cases to CDC through the National Notifiable Diseases Surveillance System. Reported cases are summarized weekly and yearly in MMWR. In addition, states are asked to submit a standardized case report form with supplementary case data to CDC's Division of Parasitic Diseases.

Results: During 2002-2007, a total of 66 cases of trichinellosis were reported to CDC. Those cases for which a supplementary case report form was not submitted or that did not meet the case definition were excluded from analysis. Of the 66 cases reported during 2002-2007, a total of 12 (18%) cases were excluded from analysis. Associated meat products were classified as either pork or meat products other than pork and were identified for 43 (80%) cases. Meat products other than pork were associated with 27 (50%) cases: 21 with bear meat, one with either bear or deer meat, one with cougar meat, one with deer meat, one with walrus or seal meat, and two with commercial beef. Pork was associated with 10 (19%) cases: seven with commercial pork, two with noncommercial pork, and one with an unspecified type of pork. Of the seven cases associated with consumption of commercial pork, five were linked to U.S. commercial pork, and two were attributed to pork ingested during travel in Asia. The two cases associated with noncommercial pork were attributed to wild boar meat; one case involved wild boar meat from a farm and the other wild boar meat from a farmers' market. Six patients reported consuming both pork and meat products other than pork, but the infected meat product could not be identified.

Interpretation: The number of reported trichinellosis cases attributed to commercial pork consumption remains low. The greatest number of cases continues to be associated with consumption of meat other than pork, especially bear meat.

Public health action: For the incidence of trichinellosis in the United States to be reduced further, education regarding safe food preparation practices and prevention of trichinellosis should be targeted toward hunters and other consumers of wild game meat, especially bear.