The association between meteorological factors and influenza incidence in Taiwan: Regional heterogeneity and...

The relationship between meteorological factors and influenza seasonality is well-established in temperate regions but remains complex and less understood in subtropical climates. This study investigates the association between key weather variables and influenza-like illness (ILI) incidence in Taiwan using real observational data from 2020 to 2025. We conducted a retrospective ecological study using publicly available data from the Taiwan Centers for Disease Control and the Central Weather Administration. Based on 4,642 complete county-week observations across 17 counties/cities, we examined four meteorological factors: temperature, relative humidity, atmospheric pressure, and precipitation. We found that relative humidity showed the strongest negative correlation with ILI incidence (r = -0.147, p < 0.001; Spearman ρ = -0.196, p < 0.001), followed by atmospheric pressure (r = -0.096, p < 0.001). Temperature and precipitation did not show statistically significant Pearson correlations (r = +0.007, p = 0.625; r = +0.020, p = 0.175, respectively). Stratified analysis across five geographic regions revealed marked heterogeneity: relative humidity was most strongly negatively correlated with ILI in Northern Taiwan (r = -0.223, p < 0.001, n = 1,095) and Central Taiwan (r = -0.196, p < 0.001, n = 934), weakly negatively associated in Southern Taiwan (r = -0.072, p = 0.032, n = 898), and paradoxically positively correlated in Eastern Taiwan (r = +0.089, p = 0.012, n = 790) and the Outlying Islands (r = +0.144, p < 0.001, n = 925). The multiple regression model including all four meteorological variables yielded R2 = 0.045, indicating that these factors collectively explain only 4.5% of the variance in ILI incidence. In Taiwan's subtropical climate, relative humidity is the most consistent meteorological predictor of influenza activity, yet its effect is geographically heterogeneous and even reverses direction in eastern and island regions. These findings underscore the need for region-specific analysis when investigating meteorological drivers of influenza in subtropical settings.