An outbreak of a rare flu strain among cats in New York City shelters has affected more than 100 animals, but the virus poses a low risk to humans, with only one confirmed illness and no evidence of it spreading beyond the five boroughs, health officials said Thursday.

The virus, identified as H7N2, a bird flu strain, has swept through shelters because the cats are physically moved from one facility to another, officials with the New York City Department of Health said. The one human case, identified after more than 350 people were screened, occurred in a veterinarian who was reported to have had prolonged, unprotected exposure to the respiratory secretions of sick cats.

Health officials say the veterinarian, who was not identified, has already recovered from the illness, which was described as mild and short-lived.

Officials with the Nassau and Suffolk Health Departments said there has been no evidence of a flu outbreak among cats on Long Island, but authorities at the state Health Department say they are monitoring the feline outbreak.

“The risk of human infection from this virus, either through contact with an infected cat or human, is thought to be low at this time,” state Health Department spokesman Ben Rosen said in an email.

He added that the outbreak has been reported to the Centers for Disease Control and Prevention, which confirmed the H7N2 strain in the affected veterinarian. State health officials are working closely with their counterparts in New York City as well as with veterinary experts at the New York State Department of Agriculture and Markets and the U.S. Department of Agriculture, Rosen said.

Before the veterinarian’s infection, there were only two documented human cases of H7N2 in the United States. One infection occurred in a person managing an outbreak of the flu virus in turkeys and chickens in 2002. The other occurred in 2003, but the source of the infection was never identified. Both patients also had a mild illness and recovered rapidly.

The most recently documented infection is the first caused by exposure to infected cats. There has been no documented human-to-human transmission, experts said Thursday.

Dr. Susan Donelan, a specialist in infectious diseases at Stony Brook University Hospital, said improved technology in recent years has allowed government laboratories to quickly identify exotic flu strains, which circulate worldwide.

“Before we had such sophisticated tools to identify a variety of strains, we didn’t really know what was out there,” said Donelan, an assistant professor of infectious diseases at Stony Brook’s School of Medicine.

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She said laboratories name flu viruses based on two proteins stippling their surfaces, hemagglutinin and neuraminidase, which give flu viruses their H and N designations.

People who have adopted cats from city shelters or rescue homes in the past three weeks should watch for symptoms in their pets, city Health Commissioner Dr. Mary T. Bassett said.

“We are contacting people who may have been exposed and offering testing as appropriate,” Bassett said.