Impact of Climate Change on Legionnaire's Disease: A Systematic Review

Legionnaires' disease is a severe atypical pneumonia caused by Legionella species, with transmission closely linked to environmental and engineered water systems. Its increasing incidence and seasonality suggest sensitivity to meteorological conditions and climate change, but relevant exposure windows and mechanisms remain incompletely synthesized.

This systematic review followed PRISMA 2020 guidelines and was registered in PROSPERO. Observational epidemiological and environmentally informative studies evaluating associations between meteorological or hydrological variables and Legionnaires' disease outcomes were included. Due to heterogeneity in study design, exposures, outcomes, and analytical methods, a structured narrative synthesis was performed.

Twenty-three studies were included. The most consistent short-term predictors of increased Legionnaires' disease incidence were rainfall, elevated relative or absolute humidity, vapor pressure, and conditions favoring aerosol persistence, usually occurring 6-14 days before symptom onset. Antecedent warm periods several weeks earlier were also associated with increased risk, supporting conditioning and amplification within engineered water systems. Additional evidence implicated hydrological factors, including low river or stream flow and flood-related disturbance, acting over longer lag periods. Environmental sampling and post-disaster studies further supported the mobilization of hidden environmental reservoirs during extreme events.

Legionnaires' disease is a climate-sensitive infection influenced by interacting short-term meteorological triggers and longer-term climatic and hydrological conditioning of water systems. Climate-aware surveillance combined with proactive water management may help reduce future disease burden under ongoing climate change.