The risk of household secondary invasive Group A Streptococcal infections after a prophylaxis policy change in the Netherlands
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Importance
Household contacts of patients with invasive group A streptococcal (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 iGAS patients rather than only those presenting with necrotising fasciitis or streptococcal toxic shock syndrome.
Objective
To estimate risk of iGAS in the general population and among household- and other contacts of primary iGAS patients, before and after the policy change.
Design
A nationwide open cohort, linking population registry data with iGAS laboratory data, for the study period April 2022-December 2024.
Setting
Population-based.
Participants
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 iGAS patients, 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 20 January 2023.
Main Outcomes and Measures
We estimated the incidence rate ratio (IRR) of iGAS during the 30-day risk period compared to unexposed person-time. Secondary attack rates among household contacts were estimated, calculating 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 contributed 51,067,977 person-years to the analysis. A total of 3,644 iGAS isolates from 3,630 unique persons was 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 to unexposed person-time. Secondary attack rate among household contacts was 0.219% (n=7) before, and 0.047% (n=7) after the policy change, adjusted OR 0.17 (95%CI 0.03-0.83).
Conclusions and relevance
In this nationwide cohort study, we observed a reduction in secondary iGAS risk among household contacts after implementation of an expanded antibiotic prophylaxis policy.
