Coxiella burnetii (Q fever), Molecular Detection, PCR, Blood
Diagnosing Coxiella burnetii infection (eg, Q fever)
Clinical Information Discusses physiology, pathophysiology, and general clinical aspects, as they relate to a laboratory test
Coxiella burnetii, the causative agent of Q fever, is a small obligate intracellular bacterium, which is distributed ubiquitously in the environment. The agent is acquired through aerosol exposure and generally causes mild respiratory disease. A small number of these acute cases will advance to a chronic condition, which typically manifests as endocarditis. If left untreated, cases of Q fever endocarditis are fatal.
Current diagnostic methods of Q fever endocarditis include serologic studies and histopathologic examination of excised cardiac tissue. These current methods are subjective and nonspecific, limiting usefulness in patient diagnostics.
Evaluation of infected tissue, blood, or serum using PCR has been shown to be an effective tool for diagnosing Coxiella burnetii infection. Mayo Medical Laboratories has developed a real-time PCR test that permits rapid identification of Coxiella burnetii.
The assay targets a unique sequence of the shikimate dehydrogenase gene (aroE) present in Coxiella burnetii.
Reference Values Describes reference intervals and additional information for interpretation of test results. May include intervals based on age and sex when appropriate. Intervals are Mayo-derived, unless otherwise designated. If an interpretive report is provided, the reference value field will state this.
A positive test is diagnostic of Coxiella burnetii disease.
A negative result does not negate the presence of the organism or active disease, as false-negative results may occur due to inhibition of PCR, sequence variability underlying the primers and probes, or the presence of Coxiella burnetii in quantities less than the limit of detection of the assay.
Cautions Discusses conditions that may cause diagnostic confusion, including improper specimen collection and handling, inappropriate test selection, and interfering substances
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 2.16 targets/mcL for EDTA whole blood.
Clinical Reference Provides recommendations for further in-depth reading of a clinical nature
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