Evaluation of the complement fixation and indirect immunofluorescence tests in the early diagnosis of primary Q fever.

A comparison was made of the performance of the commonly used complement fixation test and the more recently developed indirect immunofluorescence test in the early diagnosis of Q fever. The 303 sera tested were from 181 patients who contracted Q fever during an outbreak in Switzerland in 1983. Specific IgM antibodies were detected by the immunofluorescence test in 53% and 89% of sera obtained during the first and second week respectively after onset of illness. With the complement fixation test, the diagnosis could not be made until the second week of illness. The immunofluorescence test proved to be superior to the complement fixation test in the early detection of Q fever. Not only was it more specific but also faster and simpler to perform, permitting an earlier diagnosis on the basis of results obtained with a single serum specimen.