Low Prevalence of Anaerobic Bacteria in Pediatric Septic Arthritis Makes Obtaining Anaerobic Cultures of Questionable Value.

Background: Pediatric acute septic arthritis necessitates urgent identification and treatment to avoid irreversible joint damage if not recognized and treated in a timely manner. Many centers routinely obtain both aerobic and anaerobic cultures for the purpose of pathogen identification; however, the yield of anaerobic culture results has been called into question. The goal of this study was to determine the positivity rate of anaerobic cultures collected intraoperatively in pediatric patients with clinically diagnosed septic arthritis.

Methods: Patients with a clinical diagnosis of septic arthritis were extracted from a search of musculoskeletal infections at a large tertiary care pediatric hospital from 2007 to 2021. Cultures obtained from the operating room or through arthrocentesis were examined.

Results: We identified 470 cases of pediatric septic arthritis of which only 3 cultures were positive (0.6%) for anaerobic organisms. All cases involved a single isolate. The anaerobic bacteria that were detected included 1 facultative anaerobe, 1 strict anaerobe, and 1 relatively aerotolerant anaerobe. Four aerobic organisms grew on the anaerobic cultures. Three of the false positives also grew on aerobic culture media, whereas 1 aerobic specimen grew explicitly on anaerobic media. Neither the facultative anaerobe nor the aerotolerant anaerobe grew on aerobic culture media.

Conclusions: Over a 14-year period, only 0.6% (3 cases) of septic arthritis cases yielded positive anaerobic cultures that were not able to be cultured on aerobic media. As such, an anaerobic culture was more likely to culture a bacterium that would have also been cultured on aerobic media. In addition, a true positive anaerobic culture that would not have been diagnosed on aerobic cultures only occurs about once every 5 years at our institution. If one were to decide against obtaining anaerobic cultures, they would only miss 3 infections out of almost 500 (0.6%), and antibiotics would only have changed 0.6% of the time. These results suggest that routinely obtaining anaerobic cultures may be of limited value in pediatric septic arthritis. The false-positive rate of anaerobic labs exceeds that of true-positive cases. These results provide actionable opportunity to help guide clinician decision-making in a more cost-effective and efficient management of pediatric septic arthritis.

Level Of Evidence: IV.