Comparison of Paired Immunofluorescent Antibody Serology and Real-Time Polymerase Chain Reaction Testing for the Detection of Acute Q Fever among Febrile Patients in Kilimanjaro, Tanzania, 2012-2014.

Acute Q fever diagnosis via paired serology is problematic because it requires follow-up for convalescent sample collection; as such, it cannot provide a diagnosis to inform a treatment decision at the time of acute presentation. Real-time polymerase chain reaction (PCR) may be a useful approach for the diagnosis of acute Q fever in endemic settings. Among febrile patients enrolled in a sentinel surveillance study for Q fever at two referral hospitals in Moshi, Tanzania, from 2012 to 2014, we analyzed those with paired sera for IgG to Coxiella burnetii (C. burnetii) phase II antigens using immunofluorescent antibody (IFA) testing, and acute serum was tested for C. burnetii with PCR. Acute Q fever was defined as a fourfold or greater rise from the acute to convalescent sample in IFA reciprocal titer or PCR detection that was confirmed through repeat testing. Test characteristics were tabulated. Among 496 participants tested using both paired IFA and PCR testing, 463 (93.3%) tested negative on both IFA and PCR, five (1.0%) tested positive for Q fever on both IFA and PCR, and 28 (5.6%) tested positive for Q fever on IFA alone. The sensitivity of PCR testing using paired IFA testing as an index was 0.15 (5/33), and the specificity was 1 (463/463). C. burnetii PCR testing provides a clinically specific method that may aid in timely diagnosis in settings in which acute Q fever is a common cause of febrile illness. However, we found a low clinical sensitivity of PCR testing on serum when compared with paired IFA serology.