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expert reaction to reports of six cases of pneumonia due to unknown cause in a health centre in Tucumán, Argentina

There have been several media reports of an undiagnosed pneumonia outbreak in Argentina.


Dr Jake Dunning, Senior Research Fellow in Emerging and High Consequence Infections, Pandemic Sciences Institute, University of Oxford, said:

“The reported, currently small cluster of cases of unexplained acute severe respiratory illness in Tucuman, Argentina is a live event and investigations are ongoing; understandably there will be interest and speculation as to the cause, especially after everyone is twitchy after the pandemic events of the last two years, but we really need to await the outcome of the public health and clinical investigations, which are ongoing.  It is possible that further cases may be identified and reported going forward, as that often occurs with these sorts of events, but that does not mean this event is the start of a new pandemic.

“Some disconcerting features have been reported, however, which will cause concern to public health agencies in Argentina and to agencies in other countries, as well as the World Health Organization.  These include the reported severity of illness in many of the known cases, sadly including some fatalities, the common epidemiological link of a single health centre, and the fact that healthcare workers make up a large proportion of the recently reported cases.  This suggests, but in no way proves a common exposure source, and possibilities include exposure to a patient with an infection of unknown cause that was being cared for at a health facility, either with common exposure of multiple individuals to the same source, or initial exposure of one or two individuals and then secondary transmission between individuals.  Of course, this is purely speculative on many levels and also assumes the severe lung disease described is actually caused by an infection and, if it is an infection, seemingly it is one that may be easily transmitted to several people within the same location.  Other potential explanations include exposure to environmental agents and toxins, and the reports state this possibility is also being investigated, as one would expect.

“Although lists of all the pathogens tested for have not been made public (which is not unusual, as it’s a complicated, specialist process), available reports suggest that the clinicians have looked for and excluded many common respiratory pathogens that occur globally and are capable of causing severe acute respiratory infections, as well as some more unusual infections that occur in some parts of Argentina, including hantavirus infections and leptospirosis.  It is reassuring to hear that rapid actions are being taken by the Argentinian Ministry of Health and provincial health authorities; I expect this includes using a range of diagnostic technologies to look for alternative, specific pathogens or families of pathogens when the ‘usual suspects’ are excluded through appropriate sampling and testing.  This is in addition to detailed outbreak investigations and contact tracing by public health teams.  Reports state that control measures are also being applied, despite the cause of the outbreak being unclear; this is sensible and typical for such an event, assuming it may be a transmissible infection and applying precautionary control measures on that basis.

“Argentina has lots of experience in investigating and managing outbreaks of severe acute respiratory illness, particularly those caused by infections (e.g. pandemic H1N1 influenza, COVID-19, Andes hantavirus infection), so hopefully this cluster will remain relatively small and the underlying cause will be identified quickly.  Sharing information with WHO and with other countries, as Argentina is doing, shows commitment to Global Health Security and should be commended and supported.  In England, the experts working in UKHSA’s Epidemic Intelligence team will be monitoring this event closely, as it does for multiple events occurring globally year-round, informing and updating relevant stakeholders and performing formal risk assessments if and when they are needed.”


Dr Lance Turtle, Reader and Honorary Consultant in Infectious Diseases, University of Liverpool, and NIHR Health Protection Research Unit in Emerging and Zoonotic Infections, said:

“Pneumonia is very rarely actually diagnosed down to which specific microbe is causing it.  Not all patients with pneumonia have the same clinical features, these can vary.  If a pneumonia case looked a bit different to usual, and if there are fatalities, which seems to be the case here, then you might expect to find the cause.  But unexplained pneumonia cases probably happen frequently and are not reported, meaning it is hard to know how common things like this really are.

“At this stage it is impossible to know what the likely cause of these cases are, without more information.  It may be a viral cause, but we don’t know that yet.

“We shouldn’t be very worried at this stage.”


Dr Louise Sigfrid, Public Health Specialist and Clinical Research Fellow, ISARIC Global Support Centre, Centre for Tropical Medicine and Global Health, University of Oxford, said:

“It is a tragedy for those involved, and a concern for the affected hospital unit.

“From the information available, it is too early to say what this may be caused by until we have further information from the ongoing investigations by the Minister of Health in Argentina.

“If it 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.

“The early notification of the cases and the information provided in the PAHO briefing indicates that the authorities in Argentina are dealing with the situations using standard recognised health protection methods to identify and contain the source.”


Prof Paul Hunter, Professor in Medicine, UEA, said:

“Yesterday the Pan American Health Organization reported an outbreak of undiagnosed pneumonia in Argentina.  At present there is very little information available.  As of the 1st September there were six infections reported of whom two had already died.  The first case was a patient in a private sanatorium who started having symptoms between 18 and 22 Aug 2022.  The remaining cases were all health care workers.  Initial analyses suggests all six affected people had pneumonia.  In yesterday’s report there had been no new cases since the 22nd August.  Media reports have suggested that three more cases including an additional death have been identified but the dates of onset have not been given.  As yet initial analyses have not identified covid, or influenza or indeed any other virus or bacterial cause of the outbreak.

“Even before covid outbreaks undiagnosed respiratory infections were reported three or four times a year on promed mail, the global infectious disease early warning system.  In the three years 2017 to 2019 I counted 12 reports of undiagnosed respiratory infections reported by promed mail  Most, but not all, of these outbreaks are eventually identified as being due to a known cause and most usually fizzle out or are controlled.

“At this stage it is not possible to know whether this outbreak has been already controlled or whether it will cause further cases locally or further afield.  Most such outbreaks do not ultimately spread internationally but it is too early to judge how concerned we should be about this.  Further work should be being done to try and identify a microbial cause and also whether the likely infection may still be spreading.  Hopefully additional information should be available within coming days to enable us to better understand what if any greater risk may be involved.”


Prof Beate Kampmann, Professor of Paediatric Infection & Immunity, and Director of The Vaccine Centre, London School of Hygiene and Tropical Medicine, said:

“This limited initial report appears to refer to cases of severe pneumonia that occurred at a single health centre, and some form of nosocomial transmission (within a hospital or healthcare setting) is therefore likely – even though it is not yet clear what organism has been causing the pathology.

“In addition to running further tests for bacteria, viruses, fungi and toxicology, it is also important to understand where the patients and healthcare workers interacted to limit spread within the institution and put infection control measures in place.

“Underlying illnesses also appear to influence severity of disease.

“This is not unusual, although more detailed information is required and ongoing surveillance remains crucial to protect population and healthcare workers alike.

“It is too early to comment on whether this represents a threat to a wider population or remains restricted to the institution, or whether it might be caused by a new pathogen or one we already know about.”



Declared interests

Dr Jake Dunning: “I was previously Head of Emerging Infections and Zoonoses (which includes the Epidemic Intelligence service) at Public Health England and I currently hold an honorary consultant contract with UK Health Security Agency, for the purposes of doing research.  I am a practising NHS Consultant in Infectious Diseases and HCIDs, at the Royal Free Hospital, and Director of the NHS England High Consequence Infectious Diseases (Contact) Network.  Views expressed are my own and do not represent those of UKHSA, NHS England and NHS Improvement, the Royal Free London NHS Foundation Trust, or the UK Department of Health and Social Care.”

Dr Lance Turtle: “None.”

Dr Louise Sigfrid: “No conflicts of interest to declare.”

Prof Beate Kampmann: “No COI.”


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