US Dozens of cases of human bird influenza infection have been confirmed this year, but so far all of them have been mild.
Centers for Disease Control and Prevention confirmed on Wednesday A patient in Louisiana has been hospitalized with a severe case of avian influenza caused by the H5N1 virus. This is the first case of severe illness associated with the virus in the United States.
The virus has devastated poultry and wild bird populations across the country and infected more than 800 dairy herds in 16 states. Infected animals are spreading the virus to people who come into contact with them. Since April, the U.S. has totaled 61 bird flu cases reported in eight states. Of these, 37 had contact with sick or infected dairy cows, and 21 had contact at poultry farms or slaughter operations. In these cases, people developed conjunctivitis and mild respiratory symptoms but made a full recovery.
The severe cases are significant because avian influenza has previously caused severe illness in other countries, including outbreaks in which up to 50 percent of cases died. From 2003 to 2023, of the 878 people who tested positive for the virus; 458 deaths were reported.
An investigation by the Louisiana Department of Health and CDC determined that the hospitalized patient was a resident of southwest Louisiana who had been exposed to sick and dead birds in a backyard flock. This is the first case of H5N1 avian influenza in the United States associated with exposure to a backyard flock rather than a commercial farm.
“While the investigation into the source of this infection in Louisiana is ongoing, it is believed that the cases reported from Louisiana were exposed to sick or dead birds on their property,” CDC National Prevention said Demetre Daskalakis, director of the vaccination center. He spoke about the respiratory illness at a press conference on Wednesday. No other details regarding the source of exposure or the patient’s condition were available.
In Missouri, a person infected with bird flu was hospitalized in late August, but CDC officials said the illness was due to underlying health conditions. The patient had no respiratory symptoms or serious symptoms due to infection. “In the Missouri case, we don’t really have similar data to support that it’s associated with influenza infection,” Daskalakis said.
There are genetic similarities between the virus taken from the Louisiana patient and the virus taken from a Canadian teenager hospitalized with H5N1. Scientists have classified the Louisiana virus as type D1.1, the same type found in a patient in Canada and another in Washington state. This variant has also been detected in wild birds and poultry in the United States.
This is different from the B3.13 type that has been detected in dairy cattle, some poultry outbreaks, and sporadic human cases in multiple states. CDC scientists are conducting additional genomic sequencing of virus samples from patients in Louisiana. Genome sequencing can identify potentially concerning changes in the virus that indicate increased ability to infect humans or spread from person to person.
Human-to-human transmission of H5N1 avian influenza has not been detected. The CDC says the immediate risk to public health remains low, but people who come into contact with infected animals at work or recreationally are at high risk of contracting the virus. “This means backyard flock owners, hunters, and other bird enthusiasts should also take precautions,” the agency said in a statement.
