By Hannah Knowles

An illness resistant to multiple drugs that has hit 13 states and led to four hospitalizations is probably spread by the cutest of culprits, health officials say.

The evidence points to puppies.

Thirty people have reported infections as of Tuesday, according to the Centers for Disease Control and Prevention, which says the outbreak seems to stem mostly from dogs purchased at pet shops. About 70 percent of those sickened who were interviewed reported contact with a pet store puppy.

No single supplier has been connected to cases of the illness, which often involves bloody diarrhea and can be transmitted through animal feces. But investigations so far link 12 affected people to Petland, a national chain implicated in a previous spate of puppy-related illness involving the same kind of bacteria, campylobacter. Five of those 12 people were Petland employees, the CDC said.

Ohio-based Petland, which lists about 80 locations across the country, said in a statement that it has worked since the last outbreak to implement all recommendations from federal and state animal and public health officials.

Those protocols, the company said, include mandatory sanitary training for all employees, prominent signage and multiple sanitation stations in stores and other measures to educate staff and customers. Petland says it has also changed “animal husbandry and sanitation practices” and asked its veterinarians to use microbe-targeting substances judiciously, amid concerns about drug resistance.

“Petland takes the health and welfare of our employees, our customers and our pets very seriously,” the company said, noting that more than a third of reported cases in the new outbreak involve people in states where Petland has no stores.

Federal health officials said last year that puppies sold through Petland — which has drawn critics for its use of commercial breeders — were a likely source of the outbreak that sickened 113 people across 17 states and resulted in 23 hospitalizations.

The United States sees about 1.5 million campylobacter cases every year. The illness often results from eating raw or undercooked poultry or something with which it made contact — but it can also spread through other foods, untreated water and animals, the CDC states.

Infection symptoms for humans, beyond diarrhea, include fever and stomach cramps two to five days after exposure, according to the CDC, which says most people recover in about a week without antibiotics. But people who fall very ill or have seriously weakened immune systems may need those drugs, it says.

Analysis shows that the latest puppy-linked infections involve genetically related bacteria, suggesting a common source of infection, the CDC said. It’s also genetically related to the multi-drug resistant bacteria of the old outbreak, which began in 2016 and lasted into 2018.

The newer illnesses began between Jan. 6 and Nov. 10 of this year, the CDC says. Those sickened are as young as eight months and as old as 70 years, with a median age of 34.

The CDC is not aware of any deaths, though it notes that some illnesses may not be reported yet.

Federal officials are advising people to wash their hands after touching their dog, handling the animal’s food or cleaning up after them. They warned against letting dogs lick peoples’ mouths, faces or open wounds.

Pet owners should also get a health exam for their dog within days of bringing them home, the CDC said. And anyone who realized their dog is sick soon after purchase or adoption should go to a veterinarian, notify the group where they got their pet from and clean with water and bleach the places their pet occupied.

Dogs may have fallen ill if they seem lethargic, aren’t eating, have diarrhea or breathe abnormally, the agency said. But animals can also appear healthy and clean while carrying the germs that make people sick, it emphasized.

Petland said the CDC did not have direct recommendations for the company Monday, when it learned that the federal agency would be making its announcement. But the CDC advised the chain to seek animal health officials’ help, Petland said in its statement.

It said it will try to find the sources of infection, adding that, as with the old outbreak, the strain of bacteria implicated is not originating from “any specific Petland store.”

Petland has said that it sells puppies from federally licensed breeders who clear inspections and certifies to customers that their new pets have been examined by multiple veterinarians. But it has come under scrutiny from animal advocate groups, accused of selling puppies with inadequate health checks.

Critics expressed little surprise when the puppy-linked infections surfaced in 2017.

“It’s not hard to see how animals raised in these cramped and unsanitary conditions, trucked hundreds of miles from puppy mills to the pet stores, intermingled with other fragile young animals and handled by numerous employees and customers could become disease vectors,” Matthew Liebman, director of litigation for the Animal Legal Defense Fund, told The Post at the time.

By 2017, when the CDC announced it was investigating the earlier Campylobacter outbreak, Petland was the only major national chain selling dogs from commercial breeders, as hundreds of local jurisdictions banned shops from selling “puppy mill” animals.

Petland chief executive Joe Watson said in 2017 that all dogs can get illnesses, “just like our own kids.”

“We take every precaution possible to ensure the health of our pets,” Watson told The Post in an email.

The CDC says investigators have found eight more people infected with campylobacter after contact with a puppy at Petland but left them out of its count for the new multistate outbreak because bacterial samples were not available for whole genome sequencing, the technique used to analyze other cases.