Researchers from the Fight Against Infections Foundation have taken part in a large-scale study analysing how climate change influences the presence of Legionella in water systems and the increase in cases of Legionnaires’ disease in Catalonia. The study, recently published in the scientific journal Water Research, provides new evidence highlighting the need to adapt prevention and surveillance strategies in the face of global warming.
The study is the result of a joint effort between the Germans Trias i Pujol Research Institute (IGTP), the AQUALAB laboratory, the Public Health Agency of Catalonia, the Meteorological Service of Catalonia, and the Fight Against Infections Foundation, with the participation of Dr Pedro Botet, head of the severe bacterial infections line and co-head of the infections in immunocompromised patients line at the Foundation.
Legionella is a bacterium that occurs naturally in aquatic environments but can proliferate in artificial installations such as pipework, cold-water systems, cooling towers and ornamental fountains. When dispersed in aerosol form and inhaled, it can cause respiratory infections which, in some cases, develop into a severe pneumonia known as Legionnaires’ disease.
This bacterium thrives particularly well in warm water, between 25 and 42 °C, a range that is increasingly reached due to rising temperatures associated with climate change. This scenario creates more favourable conditions for its multiplication and increases the risk to public health.
Although previous studies had already explored the relationship between climate and cases of Legionnaires’ disease, until now there had been little information on how meteorological conditions affect artificial water systems, which are the only known source of infection.
This research, led by the Clinical and Environmental Infectious Diseases Study Group (CEID) at IGTP, is the first of its kind to be based on samples collected through routine monitoring of water systems, rather than solely on installations investigated following specific outbreaks.
The analysis includes more than 32,000 water samples collected between 2018 and 2023 (excluding 2020 due to the impact of the pandemic), all reported cases of Legionnaires’ disease in Catalonia, and meteorological data from the same period.
The results show that rising ambient temperatures and the lengthening of warm periods create ideal conditions for Legionella to increase its presence in water systems. When outdoor temperatures rise, installations such as cold-water systems or cooling towers can warm up sufficiently to allow the bacterium to multiply.
According to Elisenda Arqué, first author of the study, “prolonged heat episodes not only raise ambient temperatures, but also alter the internal conditions of water systems, making them more vulnerable to bacterial colonisation”. In the months following these episodes, cases of Legionnaires’ disease tend to increase.
One of the most relevant findings is that cold-water systems, often considered less problematic, can become critical points in contexts of intense heat. In addition, the study detects a progressive increase in positive samples over the years analysed, in parallel with the rise in reported cases.
The analysis also highlights diagnostic challenges. Within the species L. pneumophila, the most prevalent, serogroups 1 and 2–14 are equally present in the environment. However, the most commonly used diagnostic methods primarily detect serogroup 1, suggesting that a proportion of infections may go unrecorded.
In this context, the researchers emphasise that the current challenge is not only to detect Legionella, but also to anticipate high-risk periods and installations in a context of climate change—an essential aspect for protecting people who are particularly vulnerable to severe respiratory infections.
The study’s findings show that global warming is favouring the colonisation of water systems by Legionella and, as a result, the increase in Legionnaires’ disease. In light of this scenario, the authors stress the need to strengthen surveillance, adapt prevention strategies and improve clinical diagnostics.
From the Fight Against Infections Foundation, participation in studies of this kind reinforces the commitment to applied research and to generating knowledge that helps anticipate emerging risks and improve public health in a context of global change.
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