Importance Henoch-Schönlein purpura (HSP) is the most common type of vasculitis in children. The factors that trigger the disease are poorly understood. Although several viruses and seasonal bacterial infections have been associated with HSP, differentiating the specific associations of these pathogens with the onset of HSP remains a challenge due to their overlapping seasonal patterns. Objective To analyze the role of seasonal pathogens in the epidemiology of HSP. Design, Setting, and Participants This cohort study comprised an interrupted time-series analysis of patient records from a comprehensive national hospital-based surveillance system. Children younger than 18 years hospitalized for HSP in France between January 1, 2015, and March 31, 2023, were included. Exposure Implementation and relaxation of nonpharmaceutical interventions (NPIs) for the COVID-19 pandemic, such as social distancing and mask wearing. Main Outcomes and Measures The main outcomes were the monthly incidence of HSP per 100 000 children, analyzed via a quasi-Poisson regression model, and the estimated percentage of HSP incidence potentially associated with 14 selected common seasonal pathogens over the same period. Results The study included 9790 children with HSP (median age, 5 years [IQR, 4-8 years]; 5538 boys [56.4%]) and 757 110 children with the infectious diseases included in the study (median age, 0.7 years [IQR, 0.2-2 years]; 393 697 boys [52.0%]). The incidence of HSP decreased significantly after implementation of NPIs in March 2020 (−53.6%; 95% CI, −66.6% to −40.6%; P < .001) and increased significantly after the relaxation of NPIs in April 2021 (37.2%; 95% CI, 28.0%-46.3%; P < .001). The percentage of HSP incidence potentially associated with Streptococcus pneumoniae was 37.3% (95% CI, 22.3%-52.3%; P < .001), the percentage of cases associated with Streptococcus pyogenes was 25.6% (95% CI, 16.7%-34.4%; P < .001), and the percentage of cases associated with human rhino enterovirus was 17.1% (95% CI, 3.8%-30.4%; P = .01). Three sensitivity analyses found similar results. Conclusions and Relevance This study found that significant changes in the incidence of HSP simultaneously with major shifts in circulating pathogens after NPIs for the COVID-19 pandemic indicated that approximately 60% of HSP incidence was potentially associated with pneumococcus and group A streptococcus. This finding suggests that preventive measures against these pathogens could reduce the incidence of pediatric HSP.