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Canadian Journal of Infectious Diseases and Medical Microbiology
Volume 18, Issue 6, Pages 357-362
Original Article

Prevalence of USA300 Colonization or Infection and Associated Variables During an Outbreak of Community-Associated Methicillin-Resistant Staphylococcus aureus in a Marginalized Urban Population

Mark Gilbert,1,2 Judy MacDonald,3,4 Marie Louie,5,6,7,8 Dan Gregson,3,5,6,9 Kunyan Zhang,3,5,6,7,9,10 Sameer Elsayed,3,5,7,9 Kevin Laupland,3,4,5,6,9,10 Diane Nielsen,3 Virginia Wheeler,3 Tara Lye,3 and John Conly3,5,6,7,9,10

1Canadian Field Epidemiology Program, Public Health Agency of Canada, Ottawa, Ontario, Canada
2Department of Health Care and Epidemiology, University of British Columbia, Vancouver, British Columbia, Canada
3Calgary Health Region, Calgary, Alberta, Canada
4Departments of Community Health Sciences, University of Calgary, Calgary, Alberta, Canada
5Pathology and Laboratory Medicine, University of Calgary, Calgary, Alberta, Canada
6Medicine, University of Calgary, Calgary, Alberta, Canada
7Microbiology & Infectious Diseases, University of Calgary, Calgary, Alberta, Canada
8Alberta Provincial Laboratory for Public Health, Calgary, Alberta, Canada
9Calgary Laboratory Services, Calgary, Alberta, Canada
10Centre for Antimicrobial Resistance, University of Calgary, Calgary, Alberta, Canada

Received 22 May 2007; Accepted 7 August 2007

Copyright © 2007 Hindawi Publishing Corporation. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.


BACKGROUND: In 2004, an outbreak of the USA300 strain of methicillin-resistant Staphylococcus aureus (MRSA) was identified in persons with histories of homelessness, illicit drug use or incarceration in the Calgary Health Region (Calgary, Alberta). A prevalence study was conducted to test the hypotheses for factors associated with USA300 colonization or infection.

METHODS: Participants were recruited at sites accessed by this marginalized population. Health care staff administered a questionnaire and collected crack pipes and nasal, axillary and skin infection swabs. Pipes and swabs were cultured according to standard techniques. MRSA isolates were further characterized by polymerase chain reaction (mecA, Panton-Valentine leukocidin and Staphylococcal cassette chromosome mec) and typing methods (pulsed-field gel electrophoresis, staphylococcal protein A typing and multilocus sequence typing). Colonization or infection was determined by having any one of nasal, axillary, skin infection or pipe swabs positive for USA300. Colonized participants had one or more nasal, axillary or pipe swab positive for USA300; infected participants had one or more skin infection swab positive for USA300.

RESULTS: The prevalence of USA300 colonization or infection among 271 participants was 5.5% (range 3.1% to 9.0%). USA300 cases were more likely to report manipulation of skin infections (OR 9.55; 95% CI 2.74 to 33.26); use of crack pipes was not significant despite identification of the USA300 strain on two of four crack pipes tested. USA300 cases were more likely to report drug use between sex trade workers and clients (OR 5.86; 95% CI 1.63 to 21.00), and with casual sex partners (OR 5.40; 95% CI 1.64 to 17.78).

CONCLUSION: Ongoing efforts to promote the appropriate treatment of skin infections in this population are warranted. The association of USA300 colonization or infection and drug use with sexual partners suggest a role for sexual transmission of the USA300 strain of MRSA.