Evaluation of dual target-specific real-time PCR for the detection of Kingella kingae in a Danish paediatric population.

Background: We aimed to evaluate the relevance of dual target real-time polymerase chain (PCR) assays targeting the rtxA and cpn60 genes of the paediatric pathogen Kingella kingae. We also studied for the first time the clinical and epidemiological features of K. kingae infections in a Danish population.
Method: Children with K. kingae-positive cultures were identified from 11,477 children and 86 children younger than 16 years old from whom blood cultures and joint fluid cultures were obtained between January 2010 and November 2016. Results were then compared to microbiological results obtained from 29 joint fluids (28 children) tested by dual target K. kingae real-time PCR from September 2014 to November 2016. Epidemiological data of all children with microbiologically confirmed K. kingae infections were collected.
Results: From 2010 to 2016, we diagnosed 17 children with microbiological-proven K. kingae infections. During this period, blood cultures from five children and joint fluid cultures from a single child yielded K. kingae. Dual target K. kingae real-time PCR allowed us to increase the diagnostic yield of K. kingae infections by detecting the organism in 12 of 29 (41.4%) specimens. Notably, the 12 real-time PCR-positive specimens were rtxA-positive whereas only 10 (83.3%) were cpn60-positive. PCR-positive children were significantly younger than PCR-negative children (p-value: .01). A significant seasonal variation was found for patients with proven K. kingae infection (p-value: <.001), with a peak in autumn.
Conclusion: Dual target-specific real-time PCR markedly improved the detection of K. kingae in clinical specimens when compared to culture methods.