VirClia chemiluminescent assays as a tool for detecting Bartonella Henselae and Coxiella burnetii infections.

INTRODUCTION

VirClia provides an automated platform for detecting antibodies against Bartonella henselae and Coxiella burnetii.

OBJECTIVE

To assess the diagnostic performance of VirClia and identify potential sources of interference.

METHODS

A retrospective study was conducted using two independent datasets from routine clinical samples tested simultaneously by IFA and VirClia. Diagnostic performance was evaluated using Cohen's kappa and ROC curves, with IFA as the reference standard. For C. burnetii (n=1628), IgG against Phase I, Phase II, and their combination (positive if either reactive) was analyzed. For B. henselae (n=955), IgG and IgM were assessed independently. Two thresholds were defined per parameter: one ensuring 90% sensitivity and another ≥90% specificity. Intermediate values were considered within a gray zone, assumed to require IFA confirmation. The potential reduction in IFA use was estimated assuming that values outside this zone would not need confirmation. False positives (FP) were defined as VirClia values above the high-specificity threshold with a negative IFA result. Logistic regression was used to assess associations between FP results and sex, age, and symptoms. The presence of autoantibodies in FP cases was also evaluated.

RESULTS

Applying gray zone thresholds-using the manufacturer's upper cut-off (1.1) and a sensitivity-driven lower limit-yielded estimated IFA reductions of 56% for B. henselae IgG, 42% for IgM, and 79% for C. burnetii (combined phases). FP results for C. burnetii were significantly associated with extractable nuclear antigens and older age.

CONCLUSION

VirClia demonstrates strong diagnostic performance and may reduce IFA dependency when a gray zone strategy is implemented.