The World Health Organisation is monitoring a cluster of 10 cases of pneumonia from an unknown cause in Argentina in an outbreak that so far has led to three deaths.
The cases are linked to a single private clinic in the city of San Miguel de Tucuman, located in the north-west part of the country, the Pan American Health Organisation (Paho), the regional office of the WHO, reported.
An initial report on Tuesday included cases among five healthcare workers and a patient who was treated in the intensive care ward of the clinic, with symptoms developing between August 18-22.
On Thursday, local health officials reported another three cases, bringing the total to nine, including three deaths. All three people who died had other health conditions.
On Friday, Argentina reported an additional case.
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.
Michael Osterholm, an infectious disease expert at the University of Minnesota, said that given that the lungs are heavily involved, the cause is likely to be 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.
Dr Osterholm said “mystery illnesses” do sometimes happen and most often they can be explained by some local outbreak that does not have pandemic implications.
He expects more definitive information from Argentinian health officials in the next five to seven days.