Serodiagnosis of Q fever by enzyme-linked immunosorbent assay (ELISA).

Indirect enzyme-linked immunosorbent assays (ELISAs) specific for IgG and IgM antibodies against Coxiella burnetii were applied to test 208 serum samples collected within 1983 to 1986 from 128 individuals suspected of having Q fever, and from 1611 serum samples of normal blood donors. Among them were 2 patients with Q fever endocarditis, one patient with myocarditis, one patient with chronic hepatitis, 3 patients with pneumonia, one woman who had aborted a monstrous child, 38 state veterinarians, 26 farms workers, 21 persons employed in veterinary medicine, and 4 laboratory workers. Comparison with the complement fixation test (CF) revealed 46 (38%) subjects seropositive by CF and 77 (60%) seropositive by IgG and/or IgM ELISA. Among the normal blood donors 22% had antibodies to C. burnetii by ELISA. With exception of two CF titers of 1:2 and 1:8, all positive results detected by CF were confirmed by ELISA. Early stages of C. burnetii infections could be diagnosed in four cases with a single serum sample through demonstration of specific IgM by ELISA before appearance of CF antibodies. In 9 patients with acute Q fever and rising CF titers or IgG levels, diagnosis was already possible with the first serum sample by demonstration of high IgM levels by ELISA. In the two cases of endocarditis investigated, high CF titers against phase I antigen of C. burnetii confirmed the diagnosis "chronic Q fever".