Meteorological conditions and sporadic Legionnaires’ disease in Spain

Background: The incidence of legionellosis has increased in Spain in recent years, potentially influenced by climate-related changes that favour Legionella pneumophila proliferation. Aim: The main aim of this study was to evaluate whether extreme meteorological events are associated with increased sporadic legionellosis incidence. Additional objectives included examining the short-term association across increasing percentiles of each meteorological variable and describing the spatiotemporal distribution of sporadic cases in Spain from 2011 to 2023. Methods: Sporadic Legionnaires’ disease (LD) cases reported to the National Epidemiological Surveillance Network (RENAVE) between 2011 and 2023 were included. Meteorological data on daily mean temperature, cumulative precipitation, mean relative humidity and maximum wind speed from the Spanish State Meteorological Agency (AEMET) stations were aggregated by meteorological warning areas. A generalised linear mixed-effects model was applied in a sensitivity analysis to examine associations between exceeding percentile thresholds (p5–p95) for each variable and incidence 2–14 days later. A second model evaluated the association between days with extreme events (p95) and subsequent incidence. Results: A significant increase in sporadic LD was observed (p < 0.05), with the highest rates in northeastern Spain. Incidence increased progressively with higher percentiles of temperature, precipitation and humidity, while wind percentiles showed an inverse pattern. Days exceeding the 95th percentile of temperature, precipitation and humidity were associated with higher incidence; extreme wind showed no significant effect. Conclusions: Extreme temperature, precipitation and humidity are associated with short-term increases in sporadic LD. Incorporating meteorological indicators into surveillance could improve early warning and support public health interventions under changing climatic conditions.