Septic arthritis in intravenous drug abusers: a historical comparison of habits and pathogens.

BACKGROUND Intravenous drug abuse (IVDA) is a common problem; there were more than 16 million users worldwide in 2008. Numerous reports highlight the infectious skeletal complication associated with IVDA. OBJECTIVE To determine septic arthritis pathogens in IVDA in a U.S. hospital and compare the current causative organisms to a cohort from the 1980s at the same institution. METHODS An institutional review board-approved retrospective cohort study compared a consecutive series of IVDA septic arthritis patients over a 10-year period, 1999-2008 (Group B), with an IVDA septic arthritis database that was collected in the 1980s (Group A). Endpoints were: bacterial species and staph species antibiotic susceptibility. RESULTS Group B included 58 patients (35 men, 23 women) with a median age of 46.5 years. Group A included 38 patients (30 men, 8 women), with a median age of 32.5 years. The sets were significantly different in pathogens (p = 0.0443). The most common organisms were Staphylococcus (staph) species (B 74.51%, A 52.63%), followed by Streptococcus (strep) species (B 7.84%, A 31.58%), Pseudomonas (B 13.73%, A 13.16%), and Serratia (B 3.92%, A 2.63%). Of the total number of septic joints, methicillin-resistant Staphylococcus aureus (MRSA) made up 39% of Group B and 34% of Group A. However, within the staph species, MRSA made up 53% of Group B and 65% of Group A. Strep species made up 7.84% (Group B) vs. 31.58% (Group A), and Pseudomonas (13%) and Serratia (3-4%) were similar. In the Group B cohort, methicillin-susceptible Staphylococcus aureus (MSSA) had a predilection to infect the knee (94.4%), whereas MRSA was found more often in the hip (57.1%). CONCLUSIONS In IVDAs, MRSA is the most common pathogen causing septic arthritis. The ratio of staph species in septic joints is increasing, and the ratio of MRSA to MSSA remains high (>50%). Strep species are much less common.