Acute Q fever in patients with an influenza-like illness in regional New South Wales, Australia.

Introduction: Query (Q) fever is a zoonosis caused by the bacterium Coxiella burnetii typically presenting as an influenza-like illness (ILI) with or without hepatitis. The infection may be missed by clinicians in settings of low endemicity, as the presentation is clinically not specific, and there are many more common differential diagnoses for ILI including SARS-CoV-2 infection. Methods: Residual serum samples were retrospectively tested for Phase 1 and 2 Q fever-specific IgM, IgG, IgA antibodies by indirect immunofluorescence and C. burnetii DNA by polymerase chain reaction. They had not been previously tested for Q fever, originating from undiagnosed patients with probable ILI, aged 10–70 years and living in regional New South Wales, Australia. The results were compared with contemperaneous data on acute Q fever diagnostic tests which had been performed based on clinicians requests from a geographically similar population. Results: Only one (0.2%) instance of missed acute Q fever was identified after testing samples from 542 eligible patients who had probable ILI between 2016–2023. Laboratory data showed that during the same period, 731 samples were tested for acute Q fever for clinician-initiated requests and of those 70 (9.6%) were positive. Probability of being diagnosed with Q fever after a clinician initiated request was similar regardless of the patients sex, age and the calendar year of sampling. Conclusion: In this sample, Q fever was most likely to be diagnosed via clinician requested testing rather than by testing of undiagnosed patients with an influenza like illness. Author summary: Q fever is a highly contagious infection presenting as an influenza-like illness or less commonly as acute hepatitis. Literature shows that there may be diagnostic delays in recognizing Q fever by primary care physicians if they are unfamiliar with the infection. We tested residual serum samples stored at NSW Health Pathology between 2016–2023 for Q fever, if that sample originated from a rural postcode in NSW and had been tested previously for an organism causing influenza like illnesses, but not Q fever. After testing 542 eligible samples only one case of missed acute Q fever was found. In the same period, from a similar population the same diagnostic laboratory received 731 requests for Q fever testing from which 70 were positive. Therefore, In this study the number of missed acute Q fever cases were clinically insignificant. [ABSTRACT FROM AUTHOR]