Immunoglobulin responses to Coxiella burnetii (Q fever): single-serum diagnosis of acute infection, using an immunofluorescence technique.

Blood specimens were collected over various periods of time from 30 abattoir workers with a clinical diagnosis of Q fever. All specimens were tested for complement-fixing antibodies and for specific immunoglobulin M (IgM) globulins to phase 1 and 2 Coxiella burnetii organisms by an immunofluorescence technique. All 22 patients with increasing levels of complement-fixing antibodies were shown to have generated specific IgM globulins, as did 4 patients with high convalescent titers but from whom "acute" specimens were not collected. Four individuals who did not show increasing levels of complement-fixing antibodies did not produce measurable levels of specific IgM. All patients with Q fever gave positive specific IgM results by 2 weeks after the onset of symptoms. IgM to phase 1 antigen persisted for 27 weeks in one patient, but IgM to phase 2 antigen was not detectable beyond 17 weeks. The estimation of Q fever-specific IgM has proved useful in confirming infection when only a "convalescent" blood specimen is available.