Diagnosis of Acute Q Fever by Detection of Coxiella burnetii DNA using Real-Time PCR, Employing a Commercial Genesig Easy Kit

Abstract

INTRODUCTION: . Because of the danger of contracting the illness, isolation attempts are seldom made. Serological and molecular diagnostic tests are the main option. AIM: To study the prevalence of acute Q fever in Puducherry and surrounding districts of Tamil Nadu, India, employing a new commercial Real-Time Polymerase Chain Reaction (RT-PCR) kit and confirming it by the gold standard Immunofluorescence Assay (IFA). MATERIALS AND METHODS: IFA Fuller Laboratories, California, USA. Sensitivity, Specificity, Positive Predictive Value (PPV) and Negative Predictive Value (NPV) were calculated keeping IFA as the reference. RESULTS: Presumptive diagnosis of acute Q fever was made in two febrile patients by the Genesig Easy kit (2.78%). In addition to these two PCR positive cases, one more patient was positive for both Phase II IgM and Phase II IgG antibodies by the gold standard IFA. All 24 healthy controls were negative for Q fever by both PCR and IFA. The sensitivity, specificity, NPV and PPV for Genesig Easy kit PCR were: 66.67%, 100%, 100% and 98.57 % respectively against IFA as the reference. CONCLUSION: The true prevalence of Q fever in India and other developing countries is poorly understood, owing to the difficulties in the diagnosis of this infection. Since molecular diagnostic tests have good specificity and are mandated for confirmation of single acute samples, validation of commercial Q fever PCR kits is the need of the hour. Genesig Easy kit in our hands was found to be reliable with the moderate sensitivity and high specificity. Performing both PCR (with acute specimens) and IFA (with paired sera) would be ideal for Q fever diagnosis.