Serological studies of patients with cutaneous and oral-oropharyngeal anthrax from northern Thailand.

An outbreak of 52 cases of cutaneous anthrax and 24 cases of oral-oropharyngeal anthrax occurred in rural Northern Thailand in 1982, caused by contaminated water buffalo meat. Microbiologic diagnosis of many of these cases was hindered by delayed presentation for care and by prior antibiotic therapy. In a retrospective investigation, we used enzyme-linked immunosorbent assays to measure antibody titers to components of anthrax edema toxin (edema factor [EF] and protective antigen [PA]), lethal toxin (lethal factor [LF] and PA), and poly-D-glutamic acid capsule. Electrophoretic-immunotransblots (EITB, Western blot) were used to detect antibodies to PA and LF. Nine patients with cutaneous anthrax, 10 patients with oral-oropharyngeal anthrax, and 43 healthy unexposed Thai control villagers were studied. Over all, EITB was positive in 13/18 patients (sensitivity 72%) and 0/43 controls (specificity 100%). The sensitivity of the ELISA was 72% for PA, 42% for LF, 26% for EF, and 95-100% for capsule. Although a few control sera had apparent false positive titers to PA, the specificity of the ELISA confirmed by EITB (100%) demonstrated the applicability of these tests for the diagnosis of anthrax.