Pet shop puppies are thought to have caused 30 people to fall ill after coming into contact with them, the US public health institute says.
The Centers for Disease Control and Prevention is investigating an outbreak of campylobacter jejuni, which is resistant to antibiotics, across 13 US states including Florida, Minnesota and Ohio.
Four people are in hospital but nobody has died, NBC News reported.
Cases of the illness have been reported throughout the year, with patients ranging in age from eight months to 70 years.
Public health officials interviewed most of the infected people and found 88% said they had contact with a puppy.
Of those, most said it was in a pet shop.
A dozen cases were linked to the Petland chain of pet shops, including five who were employees of the company.
The bacteria is closely related to germs that infected more than 100 people during a campylobacter outbreak between 2016 and 2018.
The outbreak was also linked to pet shop puppies, the CDC said.
A CDC map shows between five and six cases have been recorded in both Minnesota and Ohio, while between two and four cases have been found in Kentucky.
Cases have also been recorded in Illinois, Georgia and South Carolina.
Petland said in a statement more than one third of the 2019 cases have been found in people living in places where it doesn’t have shops.
The company said: “Petland takes the health and welfare of our employees, our customers and our pets very seriously.
“Since an earlier outbreak in 2016, in which no specific source of infection was identified, Petland has implemented all recommended protocols from federal and state animal and public health officials to prevent human and puppy illness.”
Campylobacter causes 1.5million illness in the US each year, according to the CDC.
Symptoms include diarrhoea that’s often bloody, as well as fever and stomach cramps.
The illness usually lasts about a week and most people recover without having to take antibiotics.
Dr Jeanette O’Quin, a clinical assistant professor at Ohio State University’s College of Veterinary Medicine, said most cases involve food.
She added animal-associated illnesses are rare in comparison.
Dr O’Quin said pet shops can contain a perfect storm of risk factors for the animal-related outbreaks to occur.
She added: “Puppies from different breeding kennels get mixed together, they’re usually housed in close proximity to each other and they’re often stressed, so they’re more likely to get sick and easily spread the illness.”
People can get sick by accidentally ingesting the bacteria in the stool of an infected animal.
This can happen when a person pets a puppy before putting the unwashed hand in their mouth.
Dr O’Quin said a multi-drug resistant outbreak like this is more difficult to treat, is more costly and more likely to lead to hospitalisations.
She added it is a sign these particular bacterial strains have been exposed to a lot of antibiotics, repeatedly and over long periods of time, making them hardier and more resistant.
The CDC has said the best prevention is hygiene.
People are advised to wash their hands thoroughly with soap and water after touching a puppy or dog.