A commercially available enzyme-linked immunosorbent assay (ELISA) (Virion/Serion [Wuerzburg, Germany]), an indirect fluorescent antibody test (IFAT) (BIOS/Focus [Cypress, CA]), and a nested polymerase chain reaction (PCR) were explored for diagnosis of acute Q fever in reference to time of serum collection. Serum samples of 22 patients with acute Q fever collected around the fifth day of illness were included. A sensitivity of 30% by ELISA and 80% by IFAT (P = 0.1) was found for the first 5 days of illness and 92% by ELISA and 83% by IFAT during the sixth and eleventh day. PCR revealed a positive result in 8 cases (36%) with 6 cases deriving from the first 5 days of illness. We conclude that ELISA aids especially in the diagnosis of Q fever after 5 days of illness. The benefit of PCR as an additional tool to ELISA was especially evident in the early days of serum sampling.
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