Nonspecific reactions with the intradermal test for hydatidosis in persons with other helminth infections.

A partially purified Echinococcus antigen solution, prepared by boiling hydatid cyst fluid, was used in the intradermal test for hydatid disease in a Peruvian population. An unexpectedly high rate of positive reactions and poor agreement with serological tests suggested the presence of some agent(s) which produced cross-reactions with Echinococcus granulosus antigens in the intradermal test. Testing of hospital patients infected with a variety of helminths demonstrated nonspecific reactions in persons with Hymenolepis nana, Taenia spp., and Fasciola hepatica infections, mixed parasitisms, and several non-helminth pathological conditions. The findings contraindicated the use of the intradermal test for epidemiological surveys of hydatid disease. It is pointed out that intradermal test positivity rates cannot be used as synonymous with infection prevalence and regional differences do not necessarily reflect differences in the prevalence of E. granulosus infection. The greater specificity of some serological tests favor their use for epidemiological purposes.