title: The microbiology of impetigo in indigenous children: associations between Streptococcus pyogenes, Staphylococcus aureus, scabies, and nasal carriage.
abstract: BACKGROUND
  Impetigo is caused by both Streptococcus pyogenes and Staphylococcus aureus; the relative contributions of each have been reported to fluctuate with time and region. While S. aureus is reportedly on the increase in most industrialised settings, S. pyogenes is still thought to drive impetigo in endemic, tropical regions. However, few studies have utilised high quality microbiological culture methods to confirm this assumption. We report the prevalence and antimicrobial resistance of impetigo pathogens recovered in a randomised, controlled trial of impetigo treatment conducted in remote Indigenous communities of northern Australia.
  
  
  METHODS
  Each child had one or two sores, and the anterior nares, swabbed. All swabs were transported in skim milk tryptone glucose glycogen broth and frozen at -70°C, until plated on horse blood agar. S. aureus and S. pyogenes were confirmed with latex agglutination.
  
  
  RESULTS
  From 508 children, we collected 872 swabs of sores and 504 swabs from the anterior nares prior to commencement of antibiotic therapy. S. pyogenes and S. aureus were identified together in 503/872 (58%) of sores; with an additional 207/872 (24%) sores having S. pyogenes and 81/872 (9%) S. aureus, in isolation. Skin sore swabs taken during episodes with a concurrent diagnosis of scabies were more likely to culture S. pyogenes (OR 2.2, 95% CI 1.1 - 4.4, p = 0.03). Eighteen percent of children had nasal carriage of skin pathogens. There was no association between the presence of S. aureus in the nose and skin. Methicillin-resistance was detected in 15% of children who cultured S. aureus from either a sore or their nose. There was no association found between the severity of impetigo and the detection of a skin pathogen.
  
  
  CONCLUSIONS
  S. pyogenes remains the principal pathogen in tropical impetigo; the relatively high contribution of S. aureus as a co-pathogen has also been confirmed. Children with scabies were more likely to have S. pyogenes detected. While clearance of S. pyogenes is the key determinant of treatment efficacy, co-infection with S. aureus warrants consideration of treatment options that are effective against both pathogens where impetigo is severe and prevalent.
  
  
  BACKGROUND
  This trial is registered; ACTRN12609000858291 .
authors.affiliation: Menzies School of Health Research, Charles Darwin University, Darwin, Northern Territory, Australia. asha.bowen@menzies.edu.au.|Princess Margaret Hospital for Children, Perth, Western Australia, Australia. asha.bowen@menzies.edu.au.|Telethon Kids Institute, University of Western Australia, Perth, Western Australia, Australia. asha.bowen@menzies.edu.au.
authors.forename: Asha C
authors.initials: AC
authors.lastname: Bowen
authors.affiliation: Menzies School of Health Research, Charles Darwin University, Darwin, Northern Territory, Australia. steven.tong@menzies.edu.au.|Royal Darwin Hospital, Darwin, Northern Territory, Australia. steven.tong@menzies.edu.au.
authors.forename: Steven Y C
authors.initials: SY
authors.lastname: Tong
authors.affiliation: Telethon Kids Institute, University of Western Australia, Perth, Western Australia, Australia. mark.chatfield@menzies.edu.au.
authors.forename: Mark D
authors.initials: MD
authors.lastname: Chatfield
authors.affiliation: Princess Margaret Hospital for Children, Perth, Western Australia, Australia. jonathan.carapetis@telethonkids.org.au.|Telethon Kids Institute, University of Western Australia, Perth, Western Australia, Australia. jonathan.carapetis@telethonkids.org.au.
authors.forename: Jonathan R
authors.initials: JR
authors.lastname: Carapetis
mesh_terms: D000293:Adolescent; D001315:Australia / Q000208:ethnology; D002353:Carrier State / Q000453:epidemiology / Q000208:ethnology; D002648:Child; D002675:Child, Preschool; D060085:Coinfection; D005260:Female; D006801:Humans; D007169:Impetigo / Q000188:drug therapy / Q000208:ethnology / Q000382:microbiology*; D007223:Infant; D008297:Male; D016106:Methicillin Resistance / Q000208:ethnology; D009666:Nose / Q000382:microbiology*; D044382:Population Groups / Q000706:statistics & numerical data; D015995:Prevalence; D012141:Respiratory Tract Infections / Q000188:drug therapy / Q000208:ethnology / Q000382:microbiology; D012532:Scabies / Q000188:drug therapy / Q000208:ethnology / Q000382:microbiology*; D013203:Staphylococcal Infections / Q000188:drug therapy / Q000208:ethnology / Q000382:microbiology*; D013211:Staphylococcus aureus / Q000302:isolation & purification; D013290:Streptococcal Infections / Q000188:drug therapy / Q000208:ethnology / Q000382:microbiology*; D013297:Streptococcus pyogenes / Q000302:isolation & purification; D016896:Treatment Outcome