Evaluating the role of asymptomatic throat carriage of Streptococcus pyogenes in impetigo transmission in remote Aboriginal communities in Northern Territory, Australia: a retrospective genomic analysis

Lacey, Jake A., Marcato, Adrian J., Chisholm, Rebecca H., Campbell, Patricia T., Zachreson, Cameron, Price, David J., James, Taylah B., Morris, Jacqueline M., Gorrie, Claire L., McDonald, Malcolm I., Bowen, Asha C., Giffard, Philip M., Holt, Deborah C., Currie, Bart J., Carapetis, Jonathan R., Andrews, Ross M., Davies, Mark R., Geard, Nicholas, McVernon, Jodie, and Tong, Steven Y.C. (2023) Evaluating the role of asymptomatic throat carriage of Streptococcus pyogenes in impetigo transmission in remote Aboriginal communities in Northern Territory, Australia: a retrospective genomic analysis. The Lancet Microbe, 4 (7). e524-e533.

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Background: Streptococcus pyogenes, or group A Streptococcus (GAS), infections contribute to a high burden of disease in Aboriginal Australians, causing skin infections and immune sequelae such as rheumatic heart disease. Controlling skin infections in these populations has proven difficult, with transmission dynamics being poorly understood. We aimed to identify the relative contributions of impetigo and asymptomatic throat carriage to GAS transmission.

Methods: In this genomic analysis, we retrospectively applied whole genome sequencing to GAS isolates that were collected as part of an impetigo surveillance longitudinal household survey conducted in three remote Aboriginal communities in the Northern Territory of Australia between Aug 6, 2003, and June 22, 2005. We included GAS isolates from all throats and impetigo lesions of people living in two of the previously studied communities. We classified isolates into genomic lineages based on pairwise shared core genomes of more than 99% with five or fewer single nucleotide polymorphisms. We used a household network analysis of epidemiologically and genomically linked lineages to quantify the transmission of GAS within and between households.

Findings: We included 320 GAS isolates in our analysis: 203 (63%) from asymptomatic throat swabs and 117 (37%) from impetigo lesions. Among 64 genomic lineages (encompassing 39 emm types) we identified 264 transmission links (involving 93% of isolates), for which the probable source was asymptomatic throat carriage in 166 (63%) and impetigo lesions in 98 (37%). Links originating from impetigo cases were more frequent between households than within households. Households were infected with GAS for a mean of 57 days (SD 39 days), and once cleared, reinfected 62 days (SD 40 days) later. Increased household size and community presence of GAS and scabies were associated with slower clearance of GAS.

Interpretation: In communities with high prevalence of endemic GAS-associated skin infection, asymptomatic throat carriage is a GAS reservoir. Public health interventions such as vaccination or community infection control programmes aimed at interrupting transmission of GAS might need to include consideration of asymptomatic throat carriage.

Item ID: 79490
Item Type: Article (Research - C1)
ISSN: 2666-5247
Copyright Information: © 2023 The Author(s). Published by Elsevier Ltd. This is an Open Access article under the CC BY-NC-ND 4.0 license.
Funders: Australian National Health and Medical Research Council (NHMRC)
Projects and Grants: NHMRC GNT1145033, NHMRC GNT1117140
Date Deposited: 21 Mar 2024 00:36
FoR Codes: 45 INDIGENOUS STUDIES > 4504 Aboriginal and Torres Strait Islander health and wellbeing > 450402 Aboriginal and Torres Strait Islander biomedical and clinical sciences @ 50%
32 BIOMEDICAL AND CLINICAL SCIENCES > 3207 Medical microbiology > 320701 Medical bacteriology @ 50%
SEO Codes: 20 HEALTH > 2001 Clinical health > 200101 Diagnosis of human diseases and conditions @ 50%
21 INDIGENOUS > 2103 Aboriginal and Torres Strait Islander health > 210301 Aboriginal and Torres Strait Islander determinants of health @ 50%
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