Risk of Household Secondary Invasive Group A Streptococcal Infections After a Prophylaxis Policy Change.

Importance: Household contacts of patients with invasive group A streptococcus (iGAS) disease have an increased risk of iGAS. In the Netherlands, the iGAS public health policy was changed in January 2023, offering antibiotic prophylaxis to household contacts of all patients with iGAS rather than only those presenting with necrotizing fasciitis or streptococcal toxic shock syndrome. Objective: To estimate risk of iGAS in the general population and among household and other contacts of primary patients with iGAS, before and after the policy change. Design, Setting, and Participants: This nationwide, population-based, open cohort study, linked population registry data with iGAS laboratory data for the study period (April 2022 to December 2024). The study population consisted of all persons included in the Dutch population registry at any time during the study period. The case definition was an iGAS isolate submitted to the Netherlands Reference Laboratory for Bacterial Meningitis, with disease onset in the study period. Exposure: For contacts of primary patients with iGAS, exposure risk period was defined as the 30 days after culture date of the index patient. Exposure under the new policy was defined as all person-time after January 20, 2023. Main Outcomes and Measures: Incidence rate ratios (IRR) of iGAS during the 30-day risk period compared with unexposed person-time were estimated. Secondary attack rates among household contacts were estimated with an odds ratio (OR) to compare attack rates before and after the policy change. Estimates were adjusted for age group, sex, household socioeconomic status, and year quarter. Results: A total of 19 006 247 persons (9 467 251 male [49.8%]; 6 308 794 [33.2%] aged 20-45 years) contributed 51 067 977 person-years to the analysis. A total of 3644 iGAS isolates from 3630 unique persons were included, of which 14 were household secondary cases. The IRR for household contacts during the risk period was 235.25 (95% CI, 94.35-586.59) before and 74.00 (95% CI, 35.17-155.71) after the policy change, compared with unexposed person-time. The secondary attack rate among household contacts was 0.219% (7 individuals) before and 0.047% (7 individuals) after the policy change (adjusted OR, 0.17; 95% CI, 0.03-0.83). Conclusions and Relevance: In this nationwide cohort study, there was a reduction in secondary iGAS risk among household contacts after implementation of an expanded antibiotic prophylaxis policy, which suggests that antibiotic prophylaxis for household contacts of patients with iGAS prevents secondary iGAS infection.