Risk factors for invasive Group A Streptococcal infection in children aged 6 months to 5 years, a case-control study, the Netherlands, February-May 2023

Summary In 2022, an increase in invasive Group A Streptococcal infections (iGAS) was observed in the Netherlands. A particular increase was seen among children, therefore we aimed to assess risk factors for iGAS in children aged 6 months to 5 years. A prospective case-control study was conducted between February and May 2023. We approached parents of notified iGAS cases to complete a questionnaire on exposures during 4 weeks prior to disease onset. Controls were recruited via social media and matched to cases (10:1) on sex and birthyear. Conditional logistic regression was performed to estimate odds ratios (OR) of exposures. For the analysis we included 18 cases and 103 controls. Varicella prior to onset of iGAS disease was reported in 2 (11%) cases and 1 (1%) control (OR: 12.0, 95% CI: 1.1-139.0). Exposure to GAS-like illnesses impetigo, pharyngitis and scarlet fever was reported in 8 (44%) cases and 15 (15%) controls (OR: 7.1, 95% CI: 1.8-29.0). Our findings are in line with previous studies by identifying varicella as a risk factor for iGAS among young children and highlight the association with non-invasive GAS infections in the community as a possible source of transmission.