Outbreak in Alberta of community-acquired (USA300) methicillin-resistant Staphylococcus aureus in people with a history of drug use, homelessness or incarceration

Abstract

Background: The USA300 strain of community-acquired methiciliin-resistant Staphylococcus aureus (CA-MRSA) can cause severe infliction and is increasingly recognized as a cause of community outbreaks. In 2004, an outbreak was identified in the Calgary Health Region (CHR). Methods: MRSA isolates were identified with standard methods at a central regional laboratory and typed via pulsed-field gel electroprtoresis (PFGE). Isolates were tested by PCR for mecA, Panton-Valentine leukocidin (PVL), SCCmec, and spa genes. Cases were defined as such if a clinical isolate of the USA300 strain was noted between January 1 and September 30, 2004, and the patient had lived or traveled in CHR within 2 years before symptom onset Demographic, clinical and risk darta cm all such cases were collected from several sources for statistical analysis. A case wsas defined as high-risk if the patient had a history of drug use, homelessness or incarceration. Results: Of 40 isolates with the USA300 PFGE pattern, all tested positive for PVL, SCCmec type IVa and spa type 008. Almost all infections (39/40,98%) involved Skin and soft tissues, except for 1 death from necrotizing hemorrhagic pneumonia; a notable proportion (38%) required hospital admission or intravenous antimicrobial therapy. The outbreak centred on the high-risk population in CHR (70%; risk ratio 169.4, 95% confidence interval 86.1-333.0). Interpretation: People with histories of illicit drug use, homelf SSACSS or recent incarceration were at highest risk for infection with CA-MRSA. The emergence and spread of this virulent strain has important implications for treatment and public health in Canada. © 2006 CMA Media Inc. or its licensors.