|Values are valid only on day of printing.|
Diagnosing Coxiella burnetii infection (eg, Q fever)
Coxiella burnetii, the causative agent of Q fever, is a small obligate intracellular bacterium, which is associated with animals. It is acquired through aerosol exposure and generally causes mild respiratory disease. A small number of acute cases advance to a chronic infection, which typically manifests as endocarditis. Left untreated, Q fever endocarditis may be fatal. Serologic and histopathologic studies may be nonspecific and subjective, respectively, limiting usefulness for patient diagnosis.
Evaluation of infected tissue, blood, or serum using PCR may be a useful tool for diagnosing some cases of Coxiella burnetii infection. Mayo Medical Laboratories has developed a real-time PCR test that rapidly detects Coxiella burnetii DNA in clinical specimens by targeting a sequence of the shikimate dehydrogenase gene (aroE) unique to Coxiella burnetii.
A positive test is diagnostic of Coxiella burnetii infection.
A negative test indicates the absence of detectable Coxiella burnetii DNA, but does not negate the presence of the organism or recent disease and may occur due to sequence variability underlying primers and probes, or the presence of Coxiella burnetii in quantities less than the limit of detection of the assay.
Test results should be used as an aid in diagnosis and not be considered diagnostic in themselves. The single assay should not be used as the only criteria to form a clinical conclusion, but results should be correlated with patient symptoms and clinical presentation. A negative result does not negate the presence of the organism or active disease.
This assay was clinically validated in a blinded manner using 52 archived, formalin-fixed, paraffin-embedded heart valve specimens from patients with endocarditis. A single sample within this set determined to contain PCR inhibitors was omitted from the final analysis set. Compared with existing diagnostic data, PCR had a sensitivity of 100% (8/8) and specificity of 100% (43/43). All samples were assayed with a second PCR assay targeting the IS1111 element.(6) Complete concordance was noted between the 2 assays (P >0.999). The limit of detection (LoD) of the assay is 216 targets/mcL for fresh tissue and estimated (by Probit analysis) to be 9.7 targets/mcL in formalin-fixed paraffin-embedded tissue.
1. Marrie TJ, Raoult D: Coxiella burnetii (Q fever). In Mandell, Douglas, and Bennett's Principles and Practice of Infectious Diseases. Edited by GL Mandell, JE Bennett, R Dolin. Seventh edition. Philadelphia, PA. Churchill Livingstone/Elsevier, 2010, pp 2511-2519
2. Maurin M, Raoult D: Q fever. Clin Microbiol Rev 1999;12:518-533
3. Fenollar F, Fournier PE, Raoult D: Molecular detection of Coxiella burnetii in the sera of patients with Q fever endocarditis or vascular infection. J Clin Microbiol 2004;42:4919-4924
4. Fournier PE, Raoult D: Comparison of PCR and serology assays for early diagnosis of acute Q fever. J Clin Microbiol 2003;41:5094-5098
5. Tande A, Cunningham S, Raoult D, et al: Coxiella burnetii prosthetic joint infection-case report and assay for detection. J Clin Microbiol 2013;51:66-69
6. Frangoulidis D, Meyer H, Kahlhofer C, Splettstoesser WD: 'Real-time' PCR-based detection of Coxiella burnetii using conventional techniques. FEMS Immunol Med Microbiol 2012;64:134-136
7. CDC Releases First National Guidelines on Managing Q Fever. JAMA 2013;309(18):1887
8. Anderson A, Bijlmer H, Fournier PE, et al: Diagnosis and management of Q fever-United States, 2013: recommendations from CDC and the Q Fever Working Group. MMWR Recomm Rep 2013;62(RR-03):1-30