Hydatid disease screening: Sanpete County, Utah, 1971-1976

Between 1971 and 1976 approximately 20% (2,265) of the population of Sanpete County, Utah, was screened for hydatid disease (Echinococcus granulosus) by intradermal, indirect hemagglutination, and bentonite flocculation tests. Of 34 persons who had follow-up chest radiographs and radioisotope liver scans, 6 were found to have asymptomatic hepatic cysts. If a participant who had pulmonary cysts and negative screening tests were included, the prevalence of asymptomatic hydatid disease would be 3 per 1,000. During the same period, 82 (148 per 1,000) of 553 dogs successfully purged and examined had E. granulosus infections. Human cyst carriage was associated with dog ownership, particularly of infected dogs or in conjunction with sheep raising as the main livelihood. Combinations of immunodiagnostic tests were more efficacious in identifying cyst carriers than the tests used singly. Limitation of screening to high risk groups (e.g., sheep raisers with dogs) can reduce costs without reducing yield. Optimum management of the cyst carrier awaits further information on the natural history of asymptomatic hydatid disease.