Human Bird Flu Patient Had No Known Animal Contact

A Missouri adult who tested positive for H5 bird flu had no known contact with animals but has underlying medical conditions, according to a statement from the Centers for Disease Control and Prevention (CDC).

The case of avian influenza A (H5) was identified as part of Missouri’s normal influenza surveillance testing program, which led to potential detection of the H5 subtype that was confirmed by the CDC, according to a press release from the Missouri State Department of Health and Senior Services. To ensure privacy, the state is not providing additional information on the patient other than that the individual has recovered and been discharged home. The state reports no increase in human influenza cases and no sign of unusual influenza activity in people, including influenza-related emergency room visits, according to the press release.

Although H5 occurs mainly in wild birds and poultry, it has been identified in other animals in the United States, including dairy cows.

According to the Missouri press release, “No H5 infection in dairy cattle has been reported in Missouri; some H5 cases in commercial or backyard flocks and wild birds have been reported.” 

The case represents the 14th reported occurrence of H5 in humans in the United States in 2024 but is the first without a known occupational exposure to sick or infected animals, and additional testing to characterize the virus is underway, according to the CDC. Identification of the N (neuraminidase) in the specimen from the patient is pending; H1N1 has been identified in wild birds in Missouri in the past, but the CDC currently assesses the risk of H5N1 to the general public as low, according to the statement. 

“The main concern in these situations is that no onward transmission is occurring. Findings from the ongoing investigation will inform whether guidance changes are needed,” noted the statement.

What This Means for Clinicians

This case is the 15th case of H5N1 avian influenza in humans reported in the United States since 2022, and the interest in the case stems from the absence of currently identified animal exposure, said David Cennimo, MD, associate professor of medicine and pediatrics in the Division of Infectious Disease at Rutgers New Jersey Medical School, Newark, in an interview.

“All of the other human cases had links to sick birds or cows. We periodically see news of outbreaks in commercial chicken flocks, and there are warnings about infections in backyard chickens as well,” Cennimo said. “Wild bird populations have been affected for years and are also being monitored,” he said. 

The Missouri public health teams should be commended for their diligent surveillance and reporting as part of standard protocols, said Cennimo. “As of now, we have not been told of an obvious exposure,” he said. If in fact the patient had no occupational exposure, they may recall a dead wild bird in their yard or have some exposure as yet unknown, he said. 

“An intriguing question has been raised about the possibility of unpasteurized milk transmitting the virus,” Cennimo told Medscape. “However, there are no reports of H5N1 in Missouri cows, and we have no idea of the patient’s dietary history. I am sure detailed investigations are underway, and I would stress there is no proof that milk is a vector for virus transmission, only a theoretical possibility,” he emphasized. 

If patients have heard about the case and are expressing concern, the average person should be much more concerned about seasonal human influenza vs bird flu, especially if they are not vaccinated, Cennimo said. 

“The concern for H5N1 would be if we begin to see sustained human-to-human spread of the virus, but I would also point out to the worried well patient that the antivirals we have for influenza seem to be effective,” he added.

The patient’s unknown underlying medical conditions could have increased the risk for severe influenza, and any exposure may never be known because it was too minor to be noticed, Cennimo noted. 

For clinicians, the ongoing message is to stress seasonal influenza vaccine for everyone eligible, Cennimo told Medscape. “Consider antiviral treatment for those in whom it is recommended,” he said. In addition, “Think about the possibility of animal, especially bird, exposure. If there is concern for avian influenza, notify your health department and arrange for testing,” he said. “If you do send influenza testing and it returns positive for influenza A but not confirmed H1 or H3, the sample should be further evaluated,” Cennimo said. 

Cennimo had no conflicts to disclose.