The emergence of meticillin-resistant Staphylococcus aureus among injecting drug users

Abstract

Objective: To quantify an observed increase in meticillin-resistant Staphylococcus aureus (MRSA) infections in injecting drug users (IDUs) and, using genetic analysis and clinical presentation, contrast findings with those from previous studies in Brighton to further understanding of the clinical epidemiology and underlying molecular biology associated with the increase.

Methods: From 2006 to 2008, isolates of S. aureus were collected, together with clinical details from infected IDUs. Isolates were characterised using antibiotic susceptibilities, multilocus-sequence typing (MLST) and spa typing. The molecular epidemiology and patterns of clinical presentation were compared with results from 1999-2000 to 2000-2003.

Results: From 2006 to 2008, 18/37 (49%) of clinical isolates from IDUs were MRSA compared with 4/59 (7%) in 2000-2003 and 0/48 (0%) in 1999-2000. Despite this increase, hospital attendances by IDUs for treatment of infection dropped from 3.2 to 1.1 patients per month. MLST showed a shift in population structure towards a single MRSA clone, ST1, rather than epidemic hospital-associated strains.

Conclusion: In IDUs between 2000-2003 and 2006-2008, an increase occurred in the percentage of community-associated S. aureus isolates showing meticillin-resistance, but hospital attendances decreased. IDUs may act as a focus for the emergence of resistant S. aureus strains.