A case of swine flu has been detected in Lleida, which may be due to human-to-human transmission

It is not unusual for a swine flu virus to infect humans. Many cases go undetected because there is no epidemiological surveillance in this regard, while others go unnoticed because they are asymptomatic or because specific tests are not performed. These infections are usually mild or even asymptomatic, or cause symptoms similar to those of common flu, and are not usually transmitted between humans, or do so with very low efficiency.

The virus responsible for the 2009 pandemic, the last influenza pandemic to date, was particularly complex, combining genetic segments from swine, avian and human influenza. Its origin was traced and it was confirmed that the jump to humans came from pigs. However, it was a virus that had been recombining and evolving for years before emerging massively in humans.

In contrast, in the current case, pending final confirmation of the analyses and genetic sequences, the available data suggest that it is one of the swine flu variants circulating today. There is no indication, for now, that we are dealing with a particularly novel virus or one that behaves differently than expected. Therefore, the risk to the human population is considered low or very low.

I'm not surprised. Often, when flu is circulating, if there are no symptoms, it is not analysed in detail unless there are complications or someone goes to hospital and is tested. The fact that the patient has not had contact with animals means that they have been infected through contact with another person, who in turn may have had contact with animals or with another person in contact with animals. The thing is, flu viruses can be dangerous, they can recombine, as happened with the first pandemic of the 21st century. In addition, there may be a serious health problem in people who have a weak immune system for various reasons, both congenital and due to illness. The fact that it has been detected makes us appreciate the importance of detecting viruses that are circulating in the UK, because with this information we can be better prepared for possible complications later on.

We have requested serum from this patient because sometimes, as we use very sensitive diagnostic techniques, the cases are not always true infections. Serum has been requested to confirm this. That is pending.

The samples we have available have been sent to a WHO centre, so everything is perfectly coordinated within the network. It is true that this is a peculiar case, but it is under control. Catalonia is one of the autonomous communities that does very well in surveillance, sequencing a lot, and this is the only case we have.

So we believe that if there really were sustained circulation, we would have detected it, and that is not the case. But even so, what we can seriously attest to is that we are monitoring it. We have coordination from the autonomous community, central government, Europe and internationally.

According to published reports, this is an isolated case of swine flu detected in an 83-year-old man who has not shown any symptoms and who, according to the information available, has not had direct contact with pigs. This raises the possibility of human-to-human transmission, which can occur in exceptional cases with swine flu viruses, although it is not common or frequent.

It is important to emphasise that the fact that the patient is elderly and has had no symptoms is reassuring from a clinical point of view. At present, there are no signs of sustained transmission or an increase in cases, and such findings are usually detected precisely because of robust epidemiological surveillance systems and routine sequencing of respiratory viruses. The identification of such a case indicates that the system is working, not that we are facing a situation of public alarm.

In this context, it is appropriate to continue monitoring and epidemiological investigation to confirm the route of transmission and rule out new cases, but based on the information currently available, the risk to the general population can be considered low.

Influenza A(H1N1) virus infection in humans is frequently reported in people who have direct contact with pig farms. The absence of known exposure to animals in this case justifies specific epidemiological monitoring. However, the fact that this is an isolated case, without severe respiratory symptoms or compatible symptoms, and with no secondary cases identified to date, suggests that the risk to public health is low.

In any case, it is recommended to maintain active epidemiological surveillance and to carry out a genetic comparison with the viruses currently circulating in pig farms in the area, in order to determine the possible origin of the infection and characterise the viral evolution.

Based on what is publicly known as of the end of March 2026, an isolated case of influenza A(H1N1) variant, commonly known as “swine flu”, has been reported in Catalonia. The evidence suggests that this is not an outbreak. It is a rare finding in humans and, precisely for this reason, a very demanding protocol of confirmation and epidemiological investigation has been activated. To date, the key piece of information for interpreting the news is that there are no signs of sustained transmission. Contacts have been studied and no evidence of secondary infections has been reported. Furthermore, the case was detected in the context of surveillance and not because of typical flu symptoms. All of this is more consistent with a one-off event than with a situation of community spread. In such scenarios, it is advisable to be very cautious with hypotheses. The lack of a clear history of contact with pigs or farms may be noteworthy, but on its own it does not prove transmission between people. To support this conclusion, a consistent epidemiological chain and virological characterisation would be needed. The correct approach is to wait for full confirmation and analysis of the virus in reference laboratories, which is standard practice when a “variant” virus appears.

For the general population, the practical message is reassuring. The risk is considered very low based on the available information, and there is no reason to be alarmed or to change consumption habits. Influenza is not acquired by eating properly handled and cooked meat. It is reasonable to maintain the usual respiratory prevention measures and, in vulnerable people, to follow the health recommendations on seasonal flu prevention. If I had to take a positive message from this news, I would say that this is an example of flu surveillance working. It is detected, reported, confirmed and rigorously investigated, precisely to rule out any scenario of sustained transmission as soon as possible.