title: The turnover of strains in intermittent and persistent nasal carriers of Staphylococcus aureus.
abstract: OBJECTIVE
  We aimed to examine the dynamics of Staphylococcus aureus nasal carriage in healthy adults.
  
  
  METHODS
  Selected S. aureus strains isolated from weekly nasal swabs obtained from 122 healthy young adults over a 13 week period were spa typed.
  
  
  RESULTS
  The median duration of intermittent carriage was 4 weeks (IQR 2-6) and the median interval between episodes of carriage of different spa types was 3.5 weeks (IQR 2.25-4). 6/19 (32%) Persistent carriers were colonised with more than one spa type during the study, and in two persistent carriers a brief period of mixed colonisation with two spa types was observed. Even when the carriage strain changed, it was very rare for persistent carriers to have a period during which they were culture-negative (only 6/188 (3%) swabs submitted by persistent carriers failed to culture S. aureus).
  
  
  CONCLUSIONS
  Our results imply that at least every eight weeks a healthy young adult is exposed to S. aureus sufficient to cause a new episode of carriage among intermittent carriers. Persistent carriers are almost always colonised with S. aureus and over the course of a year there will be at least one replacement of the dominant strain.
authors.affiliation: Department of Molecular Medicine and Pathology, Faculty of Medical and Health Sciences, University of Auckland, New Zealand; NZ Institute for Advanced Study and Allan Wilson Centre for Molecular Ecology & Evolution, Massey University, Auckland 0745, New Zealand. Electronic address: s.ritchie@auckland.ac.nz.
authors.forename: S R
authors.initials: SR
authors.lastname: Ritchie
authors.affiliation: Department of Molecular Medicine and Pathology, Faculty of Medical and Health Sciences, University of Auckland, New Zealand.
authors.forename: E
authors.initials: E
authors.lastname: Isdale
authors.affiliation: Department of Preventive & Social Medicine, Dunedin School of Medicine, University of Otago, New Zealand.
authors.forename: P
authors.initials: P
authors.lastname: Priest
authors.affiliation: NZ Institute for Advanced Study and Allan Wilson Centre for Molecular Ecology & Evolution, Massey University, Auckland 0745, New Zealand; Max Planck Institute for Evolutionary Biology, Plön 24306, Germany.
authors.forename: P B
authors.initials: PB
authors.lastname: Rainey
authors.affiliation: Department of Molecular Medicine and Pathology, Faculty of Medical and Health Sciences, University of Auckland, New Zealand.
authors.forename: M G
authors.initials: MG
authors.lastname: Thomas
mesh_terms: D002353:Carrier State / Q000453:epidemiology* / Q000382:microbiology*; D005260:Female; D014644:Genetic Variation; D006801:Humans; D008137:Longitudinal Studies; D008297:Male; D058889:Molecular Typing; D009297:Nasal Mucosa / Q000382:microbiology*; D013203:Staphylococcal Infections / Q000453:epidemiology* / Q000382:microbiology*; D013205:Staphylococcal Protein A / Q000235:genetics; D013211:Staphylococcus aureus / Q000145:classification* / Q000235:genetics / Q000302:isolation & purification*; D055815:Young Adult
chemical_list: D013205:Staphylococcal Protein A
keywords: Carriage; Dynamics; Healthy adults; Staphylococcus aureus; Transmission; spa typing