Lab tests suggest that Legionella bacteria are involved in an 11-person outbreak of unexplained pneumonia cases at a private medical clinic in Tucumán
Health 5 September 2025
By Carissa Wong
The bacteria Legionella pneumophila causes Legionnaires’ disease
Janice Haney Carr/DCD
A cluster of unexplained pneumonia cases in Argentina that has led to four deaths may have been caused by Legionnaires’ disease.
The outbreak, which occurred at a private medical clinic in the Tucumán province of north-western Argentina, has so far involved 11 people. Four people are currently hospitalised, two are receiving treatments outside the clinic and one person has been discharged. The cases have included at least eight healthcare workers, two of whom have died.
The origin of the outbreak was unknown, prompting concern. Now, preliminary lab tests on two people’s lung samples have indicated the presence of the bacteria Legionella pneumophila, according to a report by the Pan American Health Organization published on 3 September.
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L. pneumophila causes Legionnaires’ disease and is commonly found in rivers, lakes and reservoirs in small quantities. Legionnaires’ disease is rare and is usually caused by inhaling tiny airborne water droplets, or aerosols, expelled from contaminated air conditioning units, humidifiers and taps.
As well as lung inflammation, common symptoms of the condition include fever, muscle aches, diarrhea, shortness of breath and headaches. Legionnaires’ disease can be treated using antibiotics, but people with more severe cases may need to be supplied with oxygen or put on a ventilator.
Researchers hope to confirm the early findings by sequencing more microbial genes from lung samples, analysing the antibodies produced by those infected and growing the microbe in the lab.
“The circumstantial evidence collected so far is consistent with Legionella, but evidence of Legionella from environmental sampling or from more established diagnostics from more of the patients would be required to give a confident confirmation,” says Martin Hibberd at the London School of Hygiene & Tropical Medicine.
“Usually, regulations stipulate that water storage and plumbing should be chemically dosed with disinfectant to prevent Legionella contamination. With a clean water system and regular checks, future cases can be prevented,” says Hibberd.
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