Prevalence of skin sores in remote Australian Aboriginal communities remains unacceptably high, with Group A Streptococcus (GAS) the dominant pathogen. We aim to better understand the drivers of GAS transmission using mathematical models. The age of first skin sores infection —the inverse of the force of infection— is quantified by synthesizing historical data across five remote Aboriginal communities.
We extracted the observed age of first skin sores infection for children under five, from three pooled studies from 2001-2007. We estimated the age of first infection using the Kaplan-Meier estimator; parametric exponential mixture model; and Cox proportional hazards. We quantified disease burden, age of first infection, proportion escaping infection and influence of cofactors.
Our study included 378 children, who presented 21 (IQR 13-27) times in their first year of life. Skin sore prevalence reached 36% in 2006. Mean age of first infection was 7.8 months (95%CI 6.9-8.8), ranging from 7-10 months across communities. Up to 7% (95%CI 6.3-12.4) escaped infection. Birth year 2006 and birth quarter October-December had significantly younger ages of first infection, at 3.9 months (95%CI 2.0-7.6) and 5.6 months (95%CI 4.1-7.5) respectively, representing an increased force of infection.
The young age of first infection with skin sores reflects the high disease burden in these communities. Quantification of the age of first infection with skin sores, and the influence of cofactors, will inform development of GAS transmission models. Surveillance of the age of first infection can be used to measure the impact of intervention strategies.