A person in Missouri with no reported exposure to animals was confirmed to have been infected with H5-type bird flu, the Missouri Department of Health and Senior Services (MDHSS) announced late Friday.

MDHSS reported that the person, who has underlying medical conditions, was hospitalized on August 22 and tested positive for an influenza A virus. Further testing at the state's public health laboratory indicated that the influenza A virus was an H5-type bird flu. The Centers for Disease Control and Prevention has now confirmed that finding and is carrying out further testing to determine if it is the H5N1 strain currently causing a widespread outbreak among US dairy cows.

It remains unclear if the person's bird flu infection was the cause of the hospitalization or if the infection was discovered incidentally. The person has since recovered and was discharged from the hospital. In its announcement, MDHSS said no other information about the patient will be released to protect the person's privacy.

The report marks the 15th human case of an H5-type bird flu infection in the country since 2022. But, the case stands out—and is quickly generating alarm online—because the man reported no contact with animals. All 14 of the previous cases occurred in farmworkers who had contact with either dairy cows or poultry that were known to be infected with H5N1.

The finding in a person without such an exposure raises the possibility that the H5N1 virus is spreading from person to person, undetected, or is spreading via an undetected animal source.

But, while the case raises concern, some infectious disease experts are cautious not to sound the alarm without more data on the case and potential exposures.

"[U]ntil such data is collected and analyzed, my level of alarm is only mildly heightened," Caitlin Rivers, a senior scholar at the Johns Hopkins Center for Health Security and founding associate director of the Center for Forecasting and Outbreak Analytics at the CDC, said online.

"I am encouraged that this case was detected through existing surveillance systems, which bodes well for our ability to identify any additional cases in the future," she added. "Federal, state, and local health officials maintained flu surveillance through the summer months in response to the H5 situation, and that was definitely the right move."

But Rivers, like many of her colleagues, has long worried about H5N1's potential to jump to humans and spark a pandemic.

To date, H5N1 is known to have infected 197 herds in 14 states. Missouri has not reported infected herds, but has reported infected poultry farms.