West-to-East transmission clusters and meteorological associations for severe hand foot and mouth disease in Shandong Province: a geospatial and GAM analysis

To analyze spatiotemporal clustering patterns of severe hand foot and mouth disease (HFMD) in children aged ≤ 5 years, quantify the associations between meteorological factors and severe HFMD incidence, and evaluate incidence shifts associated with the COVID-19 pandemic in Shandong Province, China, during 2013–2023. Spatial autocorrelation analysis (Moran’s I) and spatiotemporal cluster detection (SaTScan) identified high-risk zones. Generalized additive models (GAM) assessed nonlinear associations between meteorological factors (temperature, humidity, precipitation) and severe HFMD incidence. QGIS visualized geographic patterns. Among 763,191 HFMD cases (17,212 severe, 2.32%), annual incidence declined from 121.70/100,000 (2014) to 15.81/100,000 (2022) during COVID-19, with partial resurgence in 2023 (46.63/100,000). Severe cases exhibited significant spatial clustering (Moran’s I = 0.219–0.415; p ≤ 0.05) with westward-to-eastward high-risk cluster migration. Seasonal peaks (April–September) showed 62%–79% reductions post-2021 (p < 0.01). Temperature (ρ = 0.689, p < 0.01) and humidity (optimal threshold: 55%–60%, EDF = 2.43, p = 0.023) were the factors most strongly associated with incidence, supported by GAM: near-linear temperature effects (EDF = 1.41, p < 0.001), precipitation saturation (> 20 mm/week, EDF = 1.24, p = 0.045), and persistent seasonality (EDF = 4.02, p < 0.001). Severe HFMD epidemiology in Shandong is jointly influenced by meteorological factors (nonlinear humidity effects) and spatiotemporal dynamics, with west-to-east transmission patterns and post-pandemic behavioral-environmental interactions. Targeted vaccination and climate-adaptive surveillance during April–September peaks in identified clusters are critical for mitigation.