Molecular Insights into Q Fever: PCR-Based Detection of Coxiella burnetii from Clinical Specimens-A Retrospective Study from a Tertiary Care Hospital of North India.

Abstract

Background: Q fever, caused by Coxiella burnetii, is an underdiagnosed zoonotic disease with significant public health implications. Serological tests remain the diagnostic cornerstone but often fail in early infection. This study investigates the utility of polymerase chain reaction (PCR) targeting the IS1111 gene for molecular detection of C. burnetii in human clinical samples from a resource-limited setting.

Methods: A retrospective PCR-based study was conducted on 243 archived clinical specimens collected from febrile patients across 11 districts of North India. DNA was extracted and subjected to conventional PCR targeting the IS1111 insertion sequence. Samples positive for C. burnetii were further evaluated for coinfection with rickettsial pathogens using real-time and nested PCRs. Sequencing and phylogenetic analysis were performed on positive samples to determine genetic relationships.

Results: C. burnetii DNA was detected in 4 of 243 samples (1.64%). Half the positive cases belonged to the patients in 1-15 year age group, and two had coinfections with Orientia tsutsugamushi. One case showed coinfection with spotted fever group rickettsia. Clinical features included fever (100%), myalgia (75%), and rash (25%). Phylogenetic analysis revealed that the isolates clustered with the Z3055 reference strain, indicating a close genetic relationship to known zoonotic strains.

Conclusion: PCR targeting IS1111 is a valuable diagnostic tool for early detection of C. burnetii, particularly in settings where serological testing is delayed or unavailable. Detection in pediatric patients and coinfection with other rickettsiae underscore the need for broader diagnostic consideration of Q fever in endemic febrile illnesses.