Emerging epidemic of community-acquired methicillin-resistant Staphylococcus aureus infection in the Northern Territory

Objective: To investigate the epidemiology of WA MRSA (the recently recognised Western Australian strains of methicillin-resistant Staphylococcus aureus) in the north of the Northern Territory (NT). Design: Retrospective survey of data from hospital records. Setting: Royal Darwin Hospital (a tertiary referral hospital that serves the north of the NT) between January 1991 and July 1995. Subjects: All inpatients with clinical MRSA infection. Outcome measures: Incidence of MRSA infection, classification of MRSA as WA or EA (Eastern Australian) based on antibiotic susceptibility, patient demographic details (age, sex, ethnicity, region of residence), source of infection (nosocomial or community-acquired). Results: There were 125 WA MRSA and 93 EA MRSA infections, comprising 7% of all S. aureus infections. The incidence of WA MRSA infections consistently increased, while that of EA MRSA initially fell and then increased. All EA MRSA infections were nosocomial, while 50% of WA MRSA infections were community acquired. Rates of WA MRSA infections were highest in patients from the west region of the NT, adjacent to the Kimberley region of Western Australia (WA). Community acquired WA MRSA infections were more likely to affect Aboriginals than non-Aboriginals (relative risk [RR], 25.86; 95% confidence interval [CI], 12.51-53.47, based on population data; RR, 15.43; 95% CI, 7.85-30.32, based on admission data), as were nosocomial EA MRSA infections (RR, 2.54; 95% CI, 1.44-4.47, based on population data; RR, 2.30; 95% CI, 1.52-3.46, based on admission data). Conclusions: Changes in the epidemiology of MRSA infection in the north of the NT are consistent with the hypothesis that community-acquired WA MRSA spread into and across the NT from the Kimberley region of WA. Alternatively, crowded living conditions, hygiene difficulties and increasing use of broad spectrum antibiotics may have led to independent emergence of WA MRSA in both regions. Current infection control policies and their use in rural Aboriginal communities must be reassessed.