How human pathogens may emerge from the environment

Legionella pneumophila is an opportunistic human pathogen that is increasingly recognized as an important cause of both community and nosocomially acquired pneumonia (Legionnaires’ disease or legionellosis) worldwide. Researchers from the Institut Pasteur tried to understand how a harmless environmental bacterium can become a feared human pathogen.
This human disease represents up to 5% of community-acquired pneumonia with a high mortality rate (11% to 33%), in particular for immunocompromised and elderly people. Risk factors for developing Legionnaires’ disease are smoking, chronic heart or lung disease, diabetes, organ transplantation, immunosuppression, cancer, and age >50 years. Many of these risk factors are increasing in developed countries, as did the number of cases of Legionellosis in the last years (data from ECDC). Outbreaks affecting hundreds of people are frequently reported.

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