West-to-East Transmission Clusters and Meteorological Thresholds for Severe Hand Foot and Mouth Disease in Shandong Province: A Geospatial and GAM Analysis

Abstract Objectives: To analyze spatiotemporal clustering patterns of severe hand, foot, and mouth disease (HFMD) in children ≤5 years and quantify meteorological drivers in Shandong Province, China (2013–2023), while evaluating COVID-19-related incidence shifts. Methods: 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. results: 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 dominant drivers, supported by GAM: near-linear temperature effects (EDF=1.41, p<0.001), precipitation saturation (>20mm/week, EDF=1.24, p=0.045), and persistent seasonality (EDF=4.02, p<0.001). conclusions: Severe HFMD epidemiology in Shandong is jointly driven 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..