Primary Septic Arthritis Among Children 6 to 48 Months of Age: Implications for PCR Acquisition and Empiric Antimicrobial Selection.

Introduction Primary septic arthritis requires unique evaluation and treatment considerations for children in the 6- to 48-month age range because of the spectrum of identified pathogens and high rate of negative cultures. The purpose of this study is to evaluate primary septic arthritis in this age group in order to differentiate children with infection caused by Kingella kingae from those with other confirmed pathogens and those with no identified pathogen. Methods Preschool children who underwent multidisciplinary evaluation and treatment for septic arthritis between 2009 and 2019 were retrospectively studied. Three cohorts were established for comparison of clinical and laboratory features of primary septic arthritis: (1) confirmed K. kingae, (2) confirmed other pathogen, and (3) presumed (without identified pathogen). Results Among 139 children with septic arthritis, 40 (29%) were confirmed K. kingae, 29 (21%) other pathogen, and 70 (50%) presumed. Children with Kingella and those with presumed septic arthritis had significantly lower initial C-reactive protein (4.8 and 4.5 vs. 9.3 mg/dL) and fewer febrile hospital days (0.2 and 0.4 vs. 1.3 d) than children with other confirmed pathogens. Children with other pathogens had higher rates of bacteremia (38% vs. 0%) and positive joint fluid cultures (86% vs. 15%) than that of children with Kingella. The rate of polymerase chain reaction (PCR) acquisition was 38 of 40 (95.0%) Kingella cases, 18 of 29 (62.1%) other pathogen cases, and 33 of 70 (47.1%) presumed cases. Conclusions K. kingae was the most commonly identified pathogen among 6-month to 4-year-old children. The Kingella and other identified pathogens in this study serve to guide empiric antimicrobial recommendations for this age range. Because of similarities between children with septic arthritis because of K. kingae and those with no identified pathogen, it is likely that an unrecognized burden of Kingella resides in culture negative cases, particularly if no PCR is sent. Systematic evaluation, including PCR acquisition, and a high index of suspicion for K. kingae are recommended to thoroughly evaluate septic arthritis in preschool children. Level of evidence Level III-Retrospective cohort comparison.