People got sick because the puppies didn’t.

Or, to put it another way, contact with puppies sold at some pet stores put people at risk of multidrug-resistant bacterial infections. That’s the conclusion reached by scientists at the US Centers for Disease Control and Prevention (CDC) in a new report.

The illness is caused by bacteria called Campylobacter jejuni, which live in the digestive tracts of most dogs and puppies. Campylobacter can spread through contact with dog feces.

When NEWStat first reported on the story in October 2017, puppies sold at Petland, a national chain of about 80 pet stores, had been linked to an outbreak which, at the time, had hospitalized 13 people and sickened 55.

That number grew.

Between January 2016 and February 2018, the CDC identified 118 people from 18 states, including 29 pet store employees, who developed multidrug-resistant bacterial infections from exposure to Campylobacter bacteria.

Here’s the kicker: the antibiotic-resistant bacteria appears to have spread at least in part because healthy dogs were given antibiotics—a decision the CDC says helped fuel antibiotic resistance, a condition in which bacterial infections no longer respond to the drugs designed to treat them, due in part to overuse.

The CDC concluded that at least 105 of the people infected had been exposed to dogs before getting sick, and 101 reported contact with a pet shop puppy. In the end, the CDC traced the outbreak to puppies sold at six pet store chains, but the report says the problem likely is a broader one. Health officials in 4 states visited 20 pet stores and collected antibiotic administration records for about 150 puppies.

Of those puppies, 95% had received at least 1 course of antibiotics before reaching the store or while at the store, and at least 16 different types of antibiotics were used. About half of the puppies who received the drugs were sick. And sick puppies are a problem. But the potentially bigger problem is that the other half weren’t sick—they were healthy puppies who were given antibiotics as a preventive to keep them from getting sick. And while that might be a standard prophylactic treatment, studies show that there are documented risks of associated antibiotic resistance.

Christina Greko, DVM, PhD, an expert on antibiotic resistance with the National Veterinary Institute in Uppsala, Sweden, and the coauthor of one such study, told NEWStat that “prophylactic treatment as a routine is a really bad idea. If there are health problems . . . at the breeders, distributors, or [pet] stores, this should always be properly investigated and the underlying causes corrected.”

Some of the antibiotics given to the puppies were the same ones people became resistant to during the outbreak, suggesting that over-reliance on antibiotics for the pets may be driving the drug-resistant infections in people.

“This outbreak demonstrates that puppies can be a source of multidrug-resistant Campylobacter infections in humans, warranting a closer look at antimicrobial use in the commercial dog industry,” say the authors of the report.

But Greko warns that humans aren’t the only ones at risk. “The outbreak investigation points at potential consequences for people in contact with the pups. But there are potential consequences for the dogs as well. They may become carriers of multidrug-resistant bacteria that later in life could lead to difficult-to-treat infections.”

The CDC report also suggests that better hygiene and animal husbandry practices can reduce the need for antibiotics and decrease transmission of Campylobacter between animals and from animals to humans, and that cutting down on the use of antibiotics can reduce the number of multidrug-resistant infections.

Finally, the report concludes that “antibiotics should only be administered under veterinary supervision with a valid veterinary-client-patient relationship, consistent with existing stewardship principles.”

But while the CDC’s investigation of the outbreak has officially ended, the spread of the disease has not: The CDC warns that “the risk for multidrug-resistant Campylobacter transmission to employees and consumers continues.”

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