CDC confirms cat-to-human H5N1 case

The Centers for Disease Control and Prevention said in a May 7 report that a veterinary professional in Los Angeles County had serologic evidence of H5N1 infection after exposure to an infected domestic cat. The case emerged from an investigation into 19 cats that became ill between November 2024 and January 2025 after consuming commercially purchased raw milk, raw meat or raw pet food, according to the CDC’s Morbidity and Mortality Weekly Report. Nine of the cats tested positive for influenza A(H5N1) virus, the report said. The veterinary worker was asymptomatic, and investigators said the findings represented possible cat-to-human transmission in a clinical setting. ### Which case did the CDC actually confirm? The May 7 CDC report described one veterinary professional who developed antibodies specific to H5N1 clade 2.3.4.4.b after occupational exposure to an infected cat in Los Angeles County. The person did not report flu-like illness, had a negative nasal swab seven days after exposure, and reported no other known risk factors such as contact with backyard poultry or wild birds or consumption of raw meat or dairy products, the CDC said. (cdc.gov) Los Angeles County public health investigators and the CDC monitored 139 people who had been exposed to the 19 sick cats. Of those, 25 volunteered for serologic testing, and one tested positive for H5N1-specific antibodies, according to the report. ### How were the cats infected? During November 2024 through January 2025, 19 domestic cats in Los Angeles County became ill after consuming commercially purchased raw milk, raw meat or raw pet food, the CDC said. (cdc.gov) Nine cats tested positive for H5N1 virus, identified as clade 2.3.4.4b genotype B3.13. The CDC said pet owners should not feed raw animal products to cats. A separate CDC page for veterinarians says cats suspected or confirmed to have H5N1 can expose veterinary staff in both field and clinical settings if proper precautions are not used. (cdc.gov) ### Was there any sign of human-to-human spread? The CDC report said none of the monitored exposed people had a positive H5 influenza PCR result during symptom monitoring. The one veterinary professional with antibodies was asymptomatic, which meant the evidence came from blood testing rather than a positive diagnostic swab during acute illness. (cdc.gov) The American Veterinary Medical Association, citing the CDC investigation, said health officials continued to assess the public risk as low. (cdc.gov) The CDC report itself focused on zoonotic transmission from a domestic cat to a human and did not document human-to-human transmission. ### Why does the veterinary setting matter? The CDC said the infected worker did not use respiratory or eye protection during the exposure. (cdc.gov) The agency said the case highlighted the importance of infection-control practices in veterinary settings, especially when staff are handling cats with suspected or confirmed H5N1 infection. CDC guidance for veterinarians says staff working in close contact with suspected or confirmed H5N1-positive cats should use personal protective equipment and avoid unprotected direct contact. (avma.org) The agency has separately advised veterinarians to consider H5N1 when evaluating cats with respiratory or neurologic illness, particularly in places with infected livestock. ### What should readers watch next? The CDC’s next public updates on this episode are likely to come through its bird flu guidance pages and any additional MMWR or local public health reports tied to Los Angeles County. (cdc.gov) The May 7 report names the Los Angeles County Department of Public Health and the CDC as the agencies leading the investigation and follow-up. (cdc.gov)