Detection of Coxiella burnetii using (q)PCR: a comparison of available assays

Q fever, caused by the bacterium Coxiella burnetii, has become an emerging public health problem in the Netherlands since 2007. Diagnosis of Q fever, both in humans and animals, is mainly based on serology. Serological techniques are less suitable for direct transmission and source-finding studies for C. burnetii infection due to the delayed detection window for serological tests. The last two decades, several PCR based diagnostic assays (conventional PCR or qPCR) have been developed for the detection of C. burnetii DNA. These assays have been applied for the detection of C. burnetii DNA in clinical samples, veterinary samples, and environmental samples. These PCR-based diagnostic tests are often "in-house" developed assays. A number of commercial PCR diagnostic tests, however, have also become available. A drawback of these commercial kits is that information on some of the components is patented. This makes a thorough assessment of assay performance in relation to other "inhouse" developed assays difficult. In the current study, we describe a comparison of various (q)PCR assays used by laboratories both nationally and internationally for the detection of C. burnetii DNA. We compare the results obtained from three ring trials, set up specifically for the detection of C. burnetii DNA in human, veterinary, or environmental matrices. In addition, we compare specific parameters, such as sensitivity, specificity, and reproducibility for each of the (q)PCR assays. In conclusion, most (q)PCR assays developed for C. burnetii include detection of the multicopy insertion element IS1111, in combination with detection of other single copy genes such as icd, com1, sod, or plasmid genes. PCR based detection assays (conventional PCR or qPCR) for C. burnetii DNA preferably target short and multiple target sequences, including an internal process control in multiplex format. Other performance characteristics have not yet been published for these qPCR assays for the detection of C. burnetii, although this would be recommended