Public health officials are investigating a multidrug-resistant bacterial outbreak linked to puppies purchased from pet stores. At a most recent count, at least 30 people have been diagnosed with the highly infectious Campylobacter jejuni bacteria in 13 states, the Centers for Disease Control and Prevention (CDC) announced.

"Epidemiologic and laboratory evidence indicate that puppies purchased from pet stores are the likely source of this outbreak. Many of the cases had contact with puppies or were employees at pet stores, including Petland,” wrote the agency in a statement, adding that no single common supplier has been identified.

Illnesses were recorded in people ranging in age from 8 months to 70 years old beginning on January 6, 2019, through November 10, 2019, four of whom required hospitalizations. No deaths have been reported, though health officials warn that the bacterial strain is resistant to seven antibiotics, making it more difficult to treat. There is potential for more illnesses to be reported as the infection can take up to five days to develop symptoms and even longer for a person to report their illness to authorities.

Health investigators are working to identify illnesses that may be linked to this outbreak using a national network of public health and food coordinated by the CDC known as PulseNet. The database employs a combination of fingerprint testing and whole-genome sequencing to determine links between infected individuals. A majority of those who have reported infection are related to each other, suggesting that they share a common source of infection. Notably, this year’s strain of bacteria is related to a 2-year outbreak that began in 2016 of multidrug-resistant infections linked to pet store puppies.

People often become infected with Campylobacter when they consume something that has come into contact with the bacteria. Symptoms include bloody diarrhea, fever, abdominal cramps, as well as nausea and vomiting that usually last about a week. Though most will clear the infection on their own, people with weakened immune systems may experience life-threatening infections if the bacteria spreads to their bloodstream.

The CDC advises pet owners to wash their hands with soap and water after touching or cleaning up after their dog and before handling food. Within a few days of getting a new puppy, experts recommend taking it to the vet for a thorough examination.