The integration of Coxiella burnetii PCR testing in serum into the diagnostic algorithm of suspected acute Q fever in an endemic setting.

UNLABELLED: Serum polymerase chain reaction (PCR) for the detection of Coxiella burnetii DNA has been suggested for rapid Q fever diagnosis. We evaluated the role of PCR testing in serum in the diagnosis of acute Q fever in an endemic setting. We examined patients suspected of acute Q fever tested for C. burnetii -specific serum real-time PCR in a tertiary hospital between January 2019 toand December 2022. In the first half, PCR orders were consultation-based by infectious diseases specialists, while in the second half, they were guided by serology, positive IgM2, and negative IgG1 and IgG2, indicating early acute infection. Logistic regression analyzed independent predictors for positive PCR. PCR positivity rates were calculated using various clinical criteria in the diagnostic algorithm. Out of 272 patients, 13 (4.8%) tested positive and 130 exhibited serologically suspected early infection. Presentation during April-July and aspartate aminotransferase (AST) > 3× upper normal limit (UNL) were independently associated with positive PCR with an odds ratio (OR) = 15.03 [95% confidence interval (CI), 1.58-142.46], P = 0.018 and OR = 55.44 [95% CI, 6.16-498.69], P < 0.001, respectively. PCR positivity rate was 8.5% in serologically suspected early infection vs 1.4% in other serology, yielding OR = 6.4 [95% CI, 1.4-29.7], P = 0.009. Adding AST > 3× UNL increased OR to 49.5 [95% CI, 5.9-408.7], P ≤ 0.001 reducing required PCR tests for a single acute Q fever case from 11.8 to 3. Elevated AST in serologically suspected early Q fever is proposed to be used in a diagnostic stewardship algorithm integrating PCR in serum in an endemic setting.

IMPORTANCE: Our study suggests in a diagnostic stewardship approach the integration of molecular testing (Coxiella burnetii targeted PCR) for the diagnosis of acute Q fever in a reliable time in the endemic setting. Integrating PCR detecting Coxiella burnetii in serum in routine testing of suspected early acute Q fever based on serology result increased the PCR positivity rate significantly. Adding increased transaminases optimizes PCR utility which is highly requested particularly in endemic areas.