This conclusion follows an extensive investigation into a Missouri patient who was hospitalized with the virus in August.

This patient, notably, had no known interactions with poultry or dairy cows. In the wake of the patient's illness, several close contacts experienced respiratory symptoms, prompting health officials to carry out blood tests to check for virus transmission. Dr. Demetre Daskalakis, head of the CDC's National Center for Immunization and Respiratory Diseases, announced during a media briefing that tests on five healthcare workers who fell ill after treating the patient returned negative for H5N1.

One household contact showed potential H5 antibodies in initial tests; however, a second test could not confirm the presence of the virus. Based on these results and additional investigations, the CDC believes the individuals involved were likely infected from the same animal or animal product source, rather than through human-to-human transmission. Both the patient and household contact exhibited symptoms primarily affecting the gastrointestinal system simultaneously and have since recovered.

Dr. Nirav Shah, CDC’s principal deputy director, confirmed that different lines of evidence consistently show no person-to-person transmission. Although reassuring, the virus continues to spread from infected birds and dairy cows to humans. The general population remains at low risk, but those working closely with farm animals and wildlife are more susceptible.

In terms of outbreak impact, dairy cow infections have affected 333 herds across 14 states. In Washington, two poultry farm workers tasked with culling chickens became ill, prompting state officials to seek CDC assistance in managing the quick-evolving situation. California, reporting the highest number of human bird flu cases at 15, has also requested federal support.

Dr. Erica Pan from the California Department of Public Health highlighted the state’s proactive health checks for workers at affected farms. Infected individuals have mostly experienced mild symptoms, such as eye redness and discharge, and some respiratory illnesses. Other states with human H5N1 cases include Colorado, Michigan, and Texas.