Second Health Care Worker Linked to Missouri Bird Flu Case Also Had Symptoms: CDC

MONDAY, Sept. 23, 2024 (HealthDay News) -- Another health care worker who was exposed to a Missouri patient who tested positive for bird flu developed respiratory symptoms but wasn't tested for the flu, U.S. health officials reported Friday.

The news is rekindling worries of person-to-person transmission of the H5N1 bird flu strain.

The week before, the U.S. Centers for Disease Control and Prevention reported that a different health care worker who cared for the bird flu patient developed mild respiratory symptoms and tested negative for influenza.

Meanwhile, a person who lives with the Missouri patient also became sick but was not tested for the flu at the time. The household contact experienced gastrointestinal symptoms, the CDC said, which can be associated with an influenza infection.

"As part of the ongoing contact investigation, Missouri identified one additional health care worker contact who had developed mild respiratory symptoms and was not tested for influenza as the illness had resolved before the investigation began," the CDC said in its latest weekly flu update. 

The bird flu patient, who didn’t have known contact with poultry or dairy cows, was first hospitalized in August and tested positive for the bird flu virus. The person, who had underlying medical conditions, has since recovered, the CDC said in a statement on the case.

However, earlier this month, CDC Principal Deputy Director Dr. Nirav Shah stated on a media call that none of the patient’s close contacts showed signs or symptoms of illness, calling the case a possible “one-off.”

Since then, three contacts have been identified who had symptoms of illness, but it’s still not clear if they were sick with the bird flu.

To try to answer that question, the CDC said it has drawn blood samples from the Missouri patient and the household contact. It will perform serological testing, which looks for antibodies that could point to an H5N1 infection. Still, test results could take several weeks, the agency noted.

In its latest update, the CDC said the second health care worker wasn’t tested for influenza because the illness had resolved before the investigation began. The second health care worker will be offered the same blood test to determine if that person has antibodies for the bird flu virus.

It isn’t yet known how the Missouri patient first became infected with bird flu, the CDC said Friday.

Dr. Matthew Binnicker, director of the clinical virology laboratory at the Mayo Clinic, said the Missouri patient and the household contact may have been infected by the same source, or one might have transmitted it to the other. Both of those scenarios point to potential human-to-human spread.

“I’m really hoping that they ultimately find out that there was some likely animal exposure, because the alternative is a little bit scary,” Binnicker told NBC News.

But Dr. William Schaffner, an infectious disease expert at Vanderbilt University Medical Center in Nashville, Tenn., said if the virus has transmitted from person to person, it doesn’t necessarily mean it has become more transmissible among humans.

“Bird flu infections can be transmitted in a very limited fashion to people who have very close contact with the original patient,” Schaffner told NBC News. “That doesn’t mean that virus has picked up the genetic capacity to spread readily.”

Still, all the previous bird flu infections were among people who worked around cows and poultry, so the Missouri case raises concerns about human transmission of the virus.

"This is the 14^th human case of H5 [bird flu] reported in the United States during 2024 and the first case of H5 without a known occupational exposure to sick or infected animals," the CDC noted in a statement it released when the Missouri case first surfaced.

Bird flu has now been detected in over 200 dairy herds in 14 states, but not in Missouri, according to the CDC. Bird flu has also been found in commercial and backyard flocks and in wild birds.

This was the first bird flu case detected through routine influenza surveillance, officials noted.

More information

The CDC has more on bird flu.

SOURCES: U.S. Centers for Disease Control and Prevention, weekly flu updates, Sept. 6, Sept. 13 and Sept. 20, 2024; NBC News; New York Times