The World Health Organization is monitoring a mysterious outbreak of pneumonia that has killed three people.
There have been 10 cases linked to a private clinic in Argentina, according to the Pan American Health Organization.
The clinic is located in San Miguel de Tucuman, a town in the north-west part of the country.
An initial report on Tuesday included five healthcare workers and a patient who was treated in the intensive care ward of the clinic, with symptoms emerging late last month.
On Thursday, local health officials reported another three cases, bringing the total to nine, with an additional case confirmed on Friday.
All three people who died had other health conditions.
Symptoms have included fever, muscle and abdominal pain and shortness of breath. Several patients had pneumonia in both lungs.
Tests for known respiratory viruses and other viral, bacterial and fungal agents were all negative, PAHO said.
Biological samples have been sent to Argentina's National Administration of Laboratories and Health Institutes for additional testing, which will include an analysis for the presence of toxins.
Dr. Michael Osterholm, an infectious disease expert at the University of Minnesota, said given that the lungs are heavily involved, the cause is likely something the patients inhaled.
He first suspected Legionnaires' disease, which is caused by inhaling droplets of water containing Legionella bacteria, but tests have ruled that out.
PAHO and the WHO are monitoring the outbreak and assisting local health officials with the investigation.
Osterholm said "mystery illnesses" do sometimes happen, and most often they can be explained by some local outbreak that does not have pandemic implications.
Osterholm said he expects more definitive information from Argentine health officials in the next five to seven days.
It was reported earlier that the UK's top scientists are on high alert for the mystery pneumonia strain.
Cases of the virus were first identified on August 18, but scientists have already ruled out it being related to Covid, influenza and hantavirus, reports the Daily Star.
However, the exact symptoms are unknown to the public - with UK scientists closely monitoring the virus.
Dr Katherine Russell, Head of Emerging Infections and Zoonoses at UKHSA, said: “We are aware of an outbreak of pneumonia of unknown origin in Argentina.
“We continue to monitor the situation closely as further information becomes available through the investigations by Argentina’s health authorities.”
The epidemic intelligence team at the European Centre for Disease Control has admitted to tracking the cases since Tuesday, August 30.
