305. Enterobacteriaceae Native Joint Septic Arthritis

BACKGROUND: Native joint septic arthritis (NJSA) is commonly caused by Gram-positive organisms. Gram-negative NJSA is uncommon, and discussion is usually limited to gonococcal arthritis despite NJSA due to enterobacteriaceae being more prevalent. We aimed to describe the clinical features, treatment, and outcomes of enterobacteriaceae NJSA (ENJSA). METHODS: Cases were obtained from a previously described retrospective cohort of adult NJSA admitted to Middlemore Hospital, Auckland, and New Zealand between January 1, 2009 and December 31, 2014. ENJSA episodes were compared with non-Enterobacteriaceae NJSA (NENJSA). RESULTS: From 543 NJSA episodes identified, ENJSA were the most frequent Gram-negative group (7%, 36/543) followed by HACEK (25/543), nonfermenters (10/543), Pasteurella (9/543), and Neisseria (5/543). The median age of ENJSA cases was 50 years and 72% were male. Immune compromise was more prevalent in ENJSA (19%, 7/36) than NENJSA (8%, 42/507), P = 0.0341. The most common causative organism for ENJSA was E. coli (10/36), followed by Enterobacter cloacae (8/36) and Klebsiella pneumoniae (6/36). Polymicrobial infection was more common in ENJSA (64%, 23/36) than NENJSA (20%, 99/507), P ≤ 0.0001. All ENJSA cases were monoarticular, and 72% (26/36) affected large joints. Small joint infection was less common in ENJSA (28%, 10/36) than NENJSA (47%, 240/507), P = 0.0247. Osteomyelitis was more common in ENJSA (53%, 19/36) than NENJSA (23%, 116/507), P = 0.0002. Carbapenems and ciprofloxacin were the most commonly utilised antimicrobials for ENJSA. Clinical outcomes were worse for ENJSA, with higher rates of treatment failure (53%, 19/36) than NENJSA (15%, 76/507), P = 0.0001 (although this association did not persist on multivariate analysis of the whole cohort) and longer mean length of stay (23.2 vs. 12.8 days P = 0.0001). CONCLUSION: Enterobacteriaceae are an important and poorly described cause of NJSA, associated with immune compromise, large joint infection, polymicrobial infection, treatment failure, and increased hospital length of stay. The optimal management strategy to improve ENJSA outcomes is unknown, but may include more aggressive surgical and longer medical therapy. Further studies of ENJSA are warranted. DISCLOSURES: All authors: No reported disclosures.