The microbiology of impetigo in Indigenous children: associations between Streptococcus pyogenes, Staphylococcus aureus,scabies, and nasal carriage

Abstract

BackgroundImpetigo 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.MethodsEach 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.ResultsFrom 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.ConclusionsS. 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.Trial registrationThis trial is registered; ACTRN12609000858291.Electronic supplementary materialThe online version of this article (doi:10.1186/s12879-014-0727-5) contains supplementary material, which is available to authorized users.

The Importance of Scabies Coinfection in the Treatment Considerations for Impetigo

“…It is unlikely that this difference in treatment success is driven by the presence of MRSA in children with scabies, as there was no increased association between MRSA and scabies detection observed in logistic regression models. 22 The only microbiological association with the presence of scabies in the trial was an increased chance of detecting S. pyogenes (odds ratio, 2.2; 95% CI: 1.1-4.4%). 20 Microbiology alone cannot explain this difference in treatment success.…”

“…Our previous study found no increased association between methicillin-resistant S. aureus (MRSA) and scabies detection. 22 Most children (463/508; 91.0%) were located in the tropical region, known as the Top End with (45/508; 9.0%) living in Central Australia, a desert climate. Scabies prevalence was 17.8% in the Top End and 16.5% in Central Australia, P = 0.47.…”

Impetigo and scabies – Disease burden and modern treatment strategies

“…23 Furthermore the demonstrated frequency of co-infection of S. pyogenes with S. aureus and the emergence of CA-MRSA present additional challenges in selecting appropriate therapy. 5,6 Antibiotic treatment of affected individuals leads to resolution of impetigo lesions which likely reduces transmission. Studies to date have not explored the effect of antibiotics on rarer endpoints such as invasive infection or APSGN due to the large sample size required.…”

“…Bacterial infection, particularly with S. pyogenes and S. aureus, is a well-recognised complication of scabies infestation. 1,4,5,13 The presence of scabies is associated with complications of impetigo including invasive bacterial infection and post-streptococcal glomerulonephritis. 11,13,14 As discussed earlier, in endemic settings the treatment of scabies at a community level has been shown to reduce the prevalence and severity of skin sores 32 and haematuria.…”

“…In tropical climates Streptococcus pyogenes (Group A Streptococcus or GAS) remains the major pathogen 3,4 and co-infection with Staphylococcus aureus is common. 5 In temperate climates S. aureus has largely replaced S. pyogenes as the predominant pathogen in impetigo 6 and community acquired methicillin resistant S. aureus (CA-MRSA) is of increasing importance worldwide. 6e8…”