title: 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 methicillin-resistant Staphylococcus aureus (CA-MRSA) can cause severe infection 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 electrophoresis (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 data on all such cases were collected from several sources for statistical analysis. A case was 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).
  
  
  CONCLUSIONS
  People with histories of illicit drug use, homelessness 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.
authors.affiliation: Canadian Field Epidemiology Program, Public Health Agency of Canada, Ottawa, Ont.
authors.forename: Mark
authors.initials: M
authors.lastname: Gilbert
authors.forename: Judy
authors.initials: J
authors.lastname: MacDonald
authors.forename: Dan
authors.initials: D
authors.lastname: Gregson
authors.forename: Jennifer
authors.initials: J
authors.lastname: Siushansian
authors.forename: Kunyan
authors.initials: K
authors.lastname: Zhang
authors.forename: Sameer
authors.initials: S
authors.lastname: Elsayed
authors.forename: Kevin
authors.initials: K
authors.lastname: Laupland
authors.forename: Tom
authors.initials: T
authors.lastname: Louie
authors.forename: Karen
authors.initials: K
authors.lastname: Hope
authors.forename: Michael
authors.initials: M
authors.lastname: Mulvey
authors.forename: John
authors.initials: J
authors.lastname: Gillespie
authors.forename: Diane
authors.initials: D
authors.lastname: Nielsen
authors.forename: Virginia
authors.initials: V
authors.lastname: Wheeler
authors.forename: Marie
authors.initials: M
authors.lastname: Louie
authors.forename: Agnes
authors.initials: A
authors.lastname: Honish
authors.forename: Gloria
authors.initials: G
authors.lastname: Keays
authors.forename: John
authors.initials: J
authors.lastname: Conly
mesh_terms: D000416:Alberta / Q000453:epidemiology; D017714:Community-Acquired Infections / Q000453:epidemiology; D004196:Disease Outbreaks; D006703:Ill-Housed Persons; D006801:Humans; D016106:Methicillin Resistance; D011329:Prisoners; D018570:Risk Assessment; D012307:Risk Factors; D013203:Staphylococcal Infections / Q000453:epidemiology* / Q000635:transmission; D013211:Staphylococcus aureus / Q000187:drug effects / Q000302:isolation & purification*; D019966:Substance-Related Disorders