Q fever diagnosis in domestic ruminants: comparison between complement fixation and commercial enzyme-linked immunosorbent assays.

Q fever is an important zoonotic disease caused by infection with the bacterium Coxiella burnetii. Veterinary diagnostic laboratories, including the Veterinary Laboratories Agency (VLA) in England and Wales, have traditionally relied on the complement fixation test (CFT) for serological diagnosis. However, Q fever has assumed greater significance in recent years following several large human outbreaks linked to exposure to infected ruminants and it is essential that more reliable tests are introduced to detect the presence of C. burnetii infection in animals. The objective of the current study was to evaluate the performance of 3 commercially available enzyme-linked immunosorbent assays (ELISAs) for detection of antibodies to C. burnetii and to compare the findings with the CFT using a sample panel of 548 sera from sheep, goats, and cattle, including animals of known disease status. The statistical analysis using TAGS (test accuracy in the absence of a gold standard) software and receiver operating characteristic techniques demonstrated that the 3 ELISAs all showed improved sensitivity over the CFT. The test based on ovine antigen demonstrated the best overall performance and therefore, the VLA has adopted this test for routine use.