[Serodiagnosis of human Q-fever--demonstration of non-complement binding IgM antibodies in the enzyme-linked immunosorbent assay (ELISA)].

The application of an indirect ELISA for detection of IgM and IgG antibodies against Coxiella burnetii in five Q fever patients--among them one with endocarditis and one with hepatitis--is described. In the acute phase of infection, within a few days after onset of clinical symptoms, a significant rise of IgM antibodies could be detected. It was followed by a rise of IgG in the second and third week. In chronic Q fever endocarditis, IgM antibodies persisted over a period of nine months. High IgM and low IgG values indicated acute infection, while in convalescent sera the IgM/IgG relationship was vice versa. In a comparative investigation with complement fixation (CF) test it could be shown that CF antibodies were associated exclusively with immunoglobulin G. IgM separated from IgG by gel chromatography did not fix complement. So, the CF test does not appear to be suitable for detection of antibodies against Coxiella in the early stages of the disease. Because of the persistence of IgG antibodies over a longer period of time, sole detection of a titer against the agent is insufficient for diagnosis of current disease, if not a rise or fall in titer can be detected in a second serum sample. Using the sensitive ELISA technique, a diagnosis is usually possible with one serum sample--in connection with history and clinical investigation--by differentiation of IgM and IgG antibodies.