title: Measurement and Impact of Staphylococcus aureus Colonization Pressure in Households.
abstract: BACKGROUND
  Methicillin-resistant Staphylococcus aureus (MRSA) "colonization pressure" (CP) predicts infections in hospitals. We applied the CP concept to staphylococcal transmission within households. We tested the hypothesis that children with S aureus skin and soft tissue infection (SSTI) plus colonization ("cases") with higher baseline household CP (HHCP) would be at greater risk for persistent colonization and recurrent SSTI during study period.
  
  
  METHODS
  We collected baseline colonization swabs from 92 cases and 296 of their household contacts. Cases underwent decolonization. S aureus HHCP was calculated as the proportion of colonized household contacts at baseline (excluding cases). S aureus colonization and recurrent SSTI in cases were followed for 12 months.
  
  
  RESULTS
  Overall, median S aureus HHCP was 60% (mean = 55%). For cases colonized with MRSA, median MRSA HHCP was 11% (mean 29%); methicillin-susceptible S aureus (MSSA)-colonized cases had a median MSSA HHCP of 50% (mean = 49%). Over 1 year, MRSA HHCP was an independent risk factor for persistent MRSA colonization in cases (each 10-unit increase in HHCP associated with an adjusted odds ratio of 1.25; 95% confidence interval, 1.06-1.47). HHCP was not associated with recurrent SSTI in cases.
  
  
  CONCLUSIONS
  MRSA HHCP is associated with persistent colonization in outpatients. Further studies are needed to determine the relationship between persistent colonization of household contacts, environmental contamination, and SSTI.
authors.affiliation: Department of Pediatrics.
authors.forename: Marcela
authors.initials: M
authors.lastname: Rodriguez
authors.affiliation: Department of Pediatrics.
authors.forename: Patrick G
authors.initials: PG
authors.lastname: Hogan
authors.affiliation: Division of Biostatistics.
authors.forename: Melissa
authors.initials: M
authors.lastname: Krauss
authors.affiliation: Department of Medicine, Washington University School of Medicine, St Louis, Missouri.
authors.forename: David K
authors.initials: DK
authors.lastname: Warren
authors.affiliation: Department of Pediatrics.
authors.forename: Stephanie A
authors.initials: SA
authors.lastname: Fritz
keywords: Colonization Pressure; Methicillin-Resistant; Methicillin-Sensitive; Skin Infections; Staphylococcus aureus