The trend of urban chicken-keeping is to blame for a growing number of salmonella outbreaks across the United States, according to the Centers for Disease Control and Prevention. And bird owners exacerbate the risk by treating the chickens as they would other pets: Bringing them into the home, snuggling them, and even kissing them.

A new report set out to investigate how salmonella infections from live birds had changed, and why. From 1990 to 2014, researchers found, poultry-associated outbreaks not only became more frequent but also larger. An average of one outbreak a year was documented between 1990 and 2005, but that number crept up to four a year in the period between 2006 and 2014.

And the size of each outbreak has been growing, possibly due to infected birds being distributed widely for backyard flocks. (However birds can also contract salmonella from their new homes even if they weren’t infected when purchased.) Up to 2005, the average number of infections per outbreak was 12; from 2005 onward it was 41.

In surveys given to those infected, researchers found that the most common exposure was by baby chickens or geese.

“Backyard chickens can be a wonderful thing to have, but we’re hearing about people kissing their birds, hugging their birds, bringing them close to the face and treating them more like dogs and cats than farm animals,” said Casey Barton Behravesh, one of the report’s authors and a CDC deputy branch chief who deals with food- and animal-borne outbreaks. “It’s very important for people to know that even healthy birds can carry germs that make people sick.”

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Salmonella is a bacteria that can live in the gastrointestinal tract of chickens, geese, turkeys, and other animals. While birds carrying the bacteria can appear perfectly normal, it can cause diarrhea, vomiting, and fever when it infects humans. The bacteria can cling to birds’ feathers, bodies, beaks, and feet, and it can continue to live on couches, carpets, or countertops long after the animals have been put back into their coops.

In the last 15 years, large cities including Madison, Wis.; Denver; Ann Arbor, Mich.; and Auburn, Ala., have passed laws relaxing restrictions on residents who keep poultry. The CDC urges people with backyard chickens and other poultry to understand safe practices—always washing hands after handling, having outdoor-only boots for cleaning coops, and supervising children that interact with the birds.

Surveys also found that birds were often kept in the house instead of in coops, which Barton Behravesh said is a bad idea. “They should not be brought in the house for any reason, not even when they’re little chicks,” she said. Nearly 46 percent of respondents reported keeping poultry inside the house; of these, 22 percent reported keeping birds in the living room, 12 percent in the kitchen, 10 percent in a bedroom, and 10 percent in a bathroom.

Chickens aren’t the only instance of pets causing salmonella outbreaks. The CDC has reported a growing number of infections caused by pet reptiles like bearded dragons, geckos, and turtles, despite the fact that the FDA has banned the sale of turtles with shells smaller than four inches across.

Although this study ended in 2014, Barton Behravesh emphasized that worrisome cases are continuing to spring up. So far this year, there have been eight outbreaks linked to live poultry involving 611 people. And for every confirmed case involving a patient sick enough to actually see a doctor, the CDC estimates that 20 other people suffered a less severe form of the illness.

“We’re seeing these birds in petting zoos across the country; now there are schools that are wanting to have flocks of birds, birds being treated as therapy animals, and being brought into nursing homes,” said Barton Behravesh. “A large number of people are continuing to get ill.”

Republished with permission from STAT. This article originally appeared on September 14, 2016