CNN —
A third close contact of a patient hospitalized in Missouri with H5N1 avian influenza has also reported developing symptoms, the Centers for Disease Control and Prevention (CDC) said Friday.
The health care worker was not tested because his symptoms subsided before the illness investigation began, according to the CDC.
This is the second health care worker to report symptoms after coming into contact with a patient, and the CDC said the first was tested for influenza, which came back negative.
The agency says the risk from H5N1 to the general public remains low.
Healthcare workers are typically the first to fall ill during infectious disease outbreaks, making them of great interest to disease investigators.
But this is by no means a simple case: the patients had underlying conditions that compromised lung function, and when tested, samples showed low levels of the virus, levels that usually indicate a mild or waning infection.
“At this point, my concern index is still low,” said Dr. Michael Osterholm, director of the Center for Infectious Disease Research and Policy at the University of Minnesota, who was not involved in the Missouri study.
He points out that there are many other infectious diseases circulating that can cause respiratory symptoms.
“At the same time, COVID-19 and RSV were rampant, so we would expect that a small percentage of the population would have other respiratory symptoms than influenza,” Osterholm added. In a hospital setting, the chances of staff encountering these viruses would be even higher.
Still, the discovery of a new suspect so late in the investigation raises questions.
“It is unclear why this has not been reported in other cases, and measures to identify influenza cases early are needed,” said Dr. Seema Lakdawala, an associate professor of microbiology and immunology at the Emory University School of Medicine.
“We need more information on whether this is an influenza infection or another respiratory virus. Serological testing would be useful for all of these cases, as well as other contacts who may not have had symptoms,” said Lakdawala, who studies H5N1 virus transmission but is not involved in the Missouri investigation.
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“There is an urgent need to identify all cattle herds in all states that may be infected with the H5 virus,” she said. “It is odd that we still don’t know this information, months after the first confirmed cases of cattle infection.”
Since the first cases of avian flu were identified in dairy cows in March, 213 herds in 14 states have tested positive for the virus. No positive herds have been reported in Missouri.
It remains a mystery how the Missouri patient contracted H5N1. The Missouri Department of Health and Senior Services interviewed the patient and household contacts who became ill the same day but were not tested. They reported no contact with sick cows, birds or other animals, nor with raw milk.
Both men have since recovered from the illness. Investigators took blood samples from both men this week, which will be sent to the CDC to be tested for antibodies to the virus that causes avian flu, which could provide evidence of past infection.
