Over the weekend, health officials in Spain reportedly informed the World Health Organization (WHO) of a possible human case of swine flu that may have been caused by person-to-person transmission.
The WHO’s reference laboratory for influenza in Britain is conducting additional tests to confirm the diagnosis, according to Reuters. The patient in Spain did not have direct contact with pigs, according to the wire agency.
Even though health officials reported that the risk to the general public is low, public health experts noted that some people may be concerned about spread after the U.S. experienced dozens of human bird flu cases in 2024 and 2025.
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They told ABC News that, while the Spain case may put those who work in public health or who live in the area where it was detected on alert, widespread concern is not necessary yet.
“When we’re in any flu season, we see these sporadic swine flu cases globally,” Dr. Meghan Davis, an associate professor in the department of environmental health and engineering at Johns Hopkins Bloomberg School of Public Health, told ABC News. “If you’re in the immediate area, certainly pay really close attention to any directives from public health authorities, local health departments, et cetera.”
Davis emphasized the importance of staying informed when it comes to potential public health dangers.
“But someone who’s living at a distance, who is not working directly with animals, just having the awareness to pay attention to any health messaging around this for further guidance, that’s what I recommend,” she said.
Fabrice Coffrini/AFP via Getty Images – PHOTO: The World Health Organization headquarters in Geneva, April 23, 2025.
What is swine flu?
Swine flu is a respiratory disease commonly found in pigs, which is caused by influenza type A viruses. Just like influenza viruses found in humans, there are different subtypes and strains of swine influenza viruses.
Humans are not typically infected with swine flu viruses, but there have been reports of human infections with influenza viruses that normally circulate in swine, according to the Centers for Disease Control and Prevention (CDC).
Notably, in 2009, the H1N1 influenza virus pandemic — sometimes referred to as the swine flu pandemic and caused by bird, swine and human flu viruses — led to an estimated 60.8 million cases, 274,304 hospitalizations and 12,469 deaths in the U.S., CDC data shows.
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Occasionally, these virus strains “spill over and can infect humans, but the origin is in swine, and so the majority of these non-human influenza variants are infecting humans because they are in very close contact with swine, so they’re in the pig or pork industry,” Dr. Dean Blumberg, chief of pediatric infectious diseases at University of California, Davis Health, told ABC News.
“Those are the majority of cases, and most cases are transmitted directly to humans and there’s very few cases that are human-to-human transmission,” he added.
Should we be concerned?
Davis said she considers the Spain case to be of high concern for public health but not a major concern for the public currently.
“What that means is, those of us whose job it is to think about and worry about these always worry a bit more when there’s the potential for human-to-human transmission because that may also be a signal that the virus itself is showing characteristics of adaptation,” Davis said.
This is because the more adapted to human-to-human transmission a swine flu virus is, the greater the potential it has to go from person to person without weakening.
“But the public, there are some criteria that I think about in terms of public concern,” Davis added. “If you start hearing about something, for example, like the early days of COVID when it was clear that there were clusters that were circulating in people and that was going person to person, when you start to see a lot of that, that’s when you started to get much more concern.”
CFOTO/Future Publishing via Getty Images) – PHOTO: Pigs are raised by farmers in a rural area of Linquan County, Fuyang City, Anhui Province, China, July 11, 2022
Blumberg agrees that there’s no need for major concern yet and that the Spain case points to the need for more surveillance because of the virus’ potential to mutate.
Additionally, researchers will need to characterize the current strain to see if it is more easily transmitted from human to human, he said.
“There’s additional studies that can be done locally to see if there’s been asymptomatic infection of the population that hasn’t been detected yet,” Blumberg said. “And that will help determine whether there’s been more widespread circulation. … I think it does point to the importance of supporting public health so that they can get a handle on this to see if this is something that requires additional attention.”
