Emerging climate-related risks of legionnaires' disease and other waterborne pathogens in the United States

Despite long-standing improvements in drinking water treatment and public health regulation, Legionnaires' disease is emerging as one of the leading causes of waterborne disease-associated hospitalizations and mortality in the United States (US). Legionella spp. proliferates in engineered water systems, and accumulating evidence indicates that climate-driven environmental changes are accelerating conditions favorable for their persistence, transmission, and human exposure. This review evaluated the public health burden of Legionnaires' disease and other major waterborne pathogens in the United States and examined how climate-related factors are reshaping their epidemiology and transmission dynamics. Using a narrative review of 75 peer-reviewed studies and government reports published between 2015 and 2025, the analysis identified a sustained increase in reported Legionnaires' disease incidence since the early 2000s, with outbreaks accounting for approximately 38% of cases, 97% of hospitalizations, and nearly all reported waterborne disease-related deaths. Climate-sensitive drivers, including rising ambient and water temperatures, increased precipitation and flooding, drought-induced stagnation, and aging infrastructure, were linked to Legionella growth in premise plumbing and cooling systems, earlier seasonal peaks, and expanded geographic risk. In addition, the review documented increasing disease burden associated with Vibrio spp., Pseudomonas aeruginosa, Naegleria fowleri, Cryptosporidium, and Giardia, collectively accounting for millions of infections, over 120,000 hospitalizations, and approximately 6,600 deaths annually in the US. Findings further revealed underdiagnosis and underreporting due to reliance on passive surveillance systems and limited diagnostic testing beyond L. pneumophila serogroup 1. The reviewed evidence indicate that climate change is not only intensifying existing waterborne disease risks but also exposing critical gaps in surveillance, infrastructure resilience, and outbreak preparedness. This review highlights priority areas for climate-informed surveillance, water system management, and interdisciplinary research to reduce the risk of waterborne disease re-emergence in a changing climate.