Three people have died this week due to a pneumonia outbreak of unknown origin in the Tucumán province of northwestern Argentina
Health 2 September 2025
By Carissa Wong
X-rays have been used to diagnose nine people with pneumonia of an unknown origin in the Tucumán province of northwestern Argentina
bojanstory/Getty Images
Three people have died this week due to a pneumonia outbreak of unknown origin in the Tucumán province of northwestern Argentina.
What do we know about the mysterious pneumonia?
Nine people at a private medical clinic, including eight healthcare workers, developed pneumonia with no known cause. The known symptoms are fever, body aches and shortness of breath.
Two healthcare workers with the respiratory illness, diagnosed via X-rays of their lungs, died on 29 and 31 August.
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On 1 September it was announced that a third person had died – a 70-year-old woman who was in the centre for a surgical procedure.
The contacts of those affected are being monitored, but none have developed symptoms yet.
Who is at risk?
People with pre-existing health conditions may be at a higher risk of complications. “Underlying illnesses also appear to influence severity of disease,” Beate Kampmann at the London School of Hygiene and Tropical Medicine said in a statement to the Science Media Centre.
Speaking at a press briefing on 1 September, Luis Medina Ruiz, health minister of Tucumán, said: “All patients have some type of comorbidity, such as smoking, [chronic obstructive pulmonary disease], a history of respiratory symptoms, obesity, diabetes and high blood pressure.”
Could it be caused by a new disease?
It is possible the pneumonia was caused by a new disease, but further testing is required to establish this.
Laboratory tests have ruled out covid-19, influenza or the respiratory infection hantavirus, which mainly spreads to people from rodents.
“We first suspect[ed] covid and influenza, both influenza A and B, [and] even hantavirus, but through research they have been ruled out,” said Medina Ruiz. “We have more than 30 possible germs with the ability to detect them and they are giving negative results.”
Should I be worried that the cause is unidentified?
“I don’t think it is particularly unusual for around two weeks to have passed and for the cause to remain unidentified, as there is a necessary process and logical order of testing and ruling-out to follow,” says Jake Dunning at the University of Oxford.
“That, said, the more time that passes, the more concerns will arise about a novel pathogen,” he says. “Often, but not always, a novel pathogen is not to blame for initially unexplained events like this.”
What is being done to trace the cause?
The medical centre’s air conditioning units and water supplies are being tested for possible contamination.
“If it [a potential pathogen] is not detected by standard hospital tests available at the site, standard procedures are to send samples to specialist laboratories that have capacity to do further tests, which will take some time. This may involve testing of samples from those affected as well as environmental sampling in the healthcare centre,” Louise Sigfrid at the University of Oxford said in a statement to the Science Media Centre.
According to Dunning, “it’s best not to speculate [on the cause of the disease]. All I can say is that on the global map of newly discovered infections of humans that have occurred over the past few decades, viruses feature heavily, particularly zoonotic viruses.”
Dunning also stressed that people shouldn’t panic. “Similar events have occurred in the past where the cause was found eventually and we did not see a new pandemic,” he says.
What is the advice for people in the area?
Regular hand washing, wearing masks and social distancing can help to curb the risk of infectious diseases spreading, said Medina Ruiz.
Establishing the cause of the outbreak will help identify treatments.
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