Epidemiological Characteristics of Scarlet Fever in Liaoning Province, China: A Pre- and Post-Pandemic Comparison, 2005-2024.

OBJECTIVES: This study aimed to investigate scarlet fever epidemiology in Liaoning Province, China (2005-2024), and assess COVID-19 pandemic impacts. METHODS: Individual-level data on scarlet fever cases from the National Notifiable Infectious Disease Reporting System (NNIDRS) were analyzed for temporal, demographic and spatiotemporal features across pre-, peri- and post-pandemic stages. RESULTS: A total of 73,102 scarlet fever cases were reported. Incidence remained stable during the pre-pandemic period, from 2005 (8.9 per 100,000 population per year) to 2019 (10.8), sharply declined during the pandemic period (2020-2022; range: 1.4-0.6), and rebounded markedly post-pandemic (2023: 1.9; 2024: 7.7). Most cases (79.4%) occurred in children under 15 years of age from urban areas. During 2005-2019, incidence significantly increased among children aged 3-6 years (AAPC: 7.4%; 95% CI: 3.0%-11.9%) and in rural populations (AAPC: 4.3%; 95% CI: 1.1%-7.6%). Compared with the pre-pandemic period (2005-2019), the proportion of cases among children aged 7-14 years significantly increased during the post-pandemic period (2023-2024) (31.4% vs. 54.1%, p < 0.01). CONCLUSION: Scarlet fever incidence in Liaoning Province showed a resurgence after the pandemic, with an age distribution shifting toward older children. These evolving epidemiological patterns highlight the need for enhanced, age-targeted surveillance and adaptive prevention strategies.