Missouri sees first positive bird flu case without known animal contact

A person in Missouri who has no known contact with animals has tested positive for H5 bird flu, the state Department of Public Health and Aged Care reported Friday.

It’s the first time a patient in the U.S. outbreak has had no known exposure to sick animals. And it’s the first time someone has been hospitalized with bird flu — though it’s not yet clear whether influenza was the reason for the hospitalization or if it was incidental.

The patient, who has underlying health conditions, was hospitalized on August 22 and tested positive for influenza A. Doctors sent a sample to the Missouri public health laboratory, where it was determined to be the H5 subtype, also known as highly pathogenic avian influenza — or bird flu.

The US Centers for Disease Control and Prevention (CDC) confirmed that it was an H5 virus and said they were further examining the sample.

In previous efforts, officials have sought to understand whether human cases are caused by the strain that has been circulating among wild birds and mammals in the U.S. since 2022, or whether it is more closely related to the variant in dairy cows. They will also likely look to see whether it has acquired mutations that make it more contagious or virulent among people.

In an exclusive interview with the Guardian in July, Nirav Shah, deputy director of the CDC, said there are several concerns that officials are watching in this outbreak.

“One of them is the increasing severity of the disease,” for example if someone is hospitalized or dies from bird flu, he said.

The earlier cases in the US were mild, but they occurred among farm workers, who are generally healthy and robust. In the broader population, especially among people with other health problems, bird flu could prove more dangerous. Globally, the fatality rate hovers around 50% of confirmed cases, although there are likely less severe cases that go undetected.

“The second would be the nature of the transmission,” Shah said. “Are we seeing person-to-person transmission?”

In the two decades since H5N1 was identified in humans, further transmission of the virus between people has been extremely rare, he said.

Another major concern about virus transmission is who gets sick.

“If we were to see individuals who had no connection to a farm at all, or who had exposure to chickens, and they were developing signs and symptoms, that would be very concerning,” Shah said. “Even if there was no other route of transmission identified, that would be a sign that something else was going on.”

Officials will likely continue to trace the patient’s possible exposures and contacts with other people to see how the virus is spreading.

Avian influenza usually occurs in domestic and wild birds, but in recent years the disease has spread significantly and is now circulating in many mammals, including dairy cows and other livestock.

Two indoor cats in Colorado recently tested positive for the virus. House mice have also tested positive.

No bird flu has been detected in cows in Missouri, but the disease has been found in poultry and wild birds.

According to the Missouri press release, it can “sometimes infect people through close contact with infected animals or contaminated environments.”

This is the 15^and cases of bird flu among humans in the US since 2022 – and the 14^and this year. This is the first known human case of bird flu in Missouri.

The patient had recovered and was released from the hospital, the Missouri statement said.

• This article was updated on September 6, 2024, to correct that the Missouri Department of Health and Senior Care, not the state Department of Agriculture, made the announcement about a person testing positive for H5 bird flu.