Evaluation of a Real-Time PCR Assay for Simultaneous Detection of Kingella kingae and Staphylococcus aureus from Synovial Fluid in Suspected Septic Arthritis

Direct plating of synovial fluid (SF) on agar-based media often fails to identify pathogens in septic arthritis (SA). We developed a PCR assay for the simultaneous detection of Kingella kingae and Staphylococcus aureus from SF to evaluate molecular detection in SF and to estimate the incidence of K. kingae in SA in North America. The assay was based on detection of the cpn60 gene of K. kingae and the spa gene of S. aureus in multiplex real-time PCR. K. kingae was identified in 50% of patients between 0 and 5 yr of age (n=6) but not in any patients >18 yr old (n=105). Direct plating of SF on agar-based media failed to detect K. kingae in all samples. The PCR assay was inferior to the culture-based method for S. aureus, detecting only 50% of culture-positive cases. Our findings suggest that K. kingae is a common pathogen in pediatric SA in North America, in agreement with previous reports from Europe. PCR-based assays for the detection of K. kingae may be considered in children with SA, especially in those with a high degree of clinical suspicion.