Bird Flu Migrates from Poultry to Dairy Herds: Missouri Case Sparks Investigations

A second healthcare worker in Missouri showing symptoms after contact with a bird flu patient has not been tested. The total number of symptomatic contacts is three, all have recovered. The CDC and Missouri are investigating. Blood samples are being considered to look for antibodies, amid concerns of virus mutation.

A second Missouri healthcare worker who had contact with a hospitalized patient infected with bird flu developed mild respiratory symptoms but was not tested for the virus, U.S. officials said on Friday. The number of people who were in contact with the hospitalized bird flu patient in Missouri and developed symptoms is now up to three, officials said. All three have recovered.

The other two symptomatic cases included a healthcare worker who tested negative for influenza and a household contact of the patient who developed symptoms at the same time as the hospitalized patient, but was never tested. Unlike prior U.S. bird flu cases this year, the Missouri patient had no known contact with infected animals, raising concerns the virus currently circulating in dairy cattle may have mutated in a way that makes it spread more easily in people.

CDC officials said in a Sept. 12 briefing the agency has been unable to determine if the Missouri case was related to the virus infecting U.S. dairy cattle. Missouri is leading the state's bird flu investigation with remote assistance from the CDC.

The state's health officials said in an email last week Missouri is considering taking blood samples to look for antibodies that would indicate prior exposure to bird flu. The CDC said serologic testing will be offered to the second healthcare worker. Caitlin Rivers, an epidemiologist at Johns Hopkins Center for Health Security, said the results of the blood tests will be critical.

"We'll need the serology results to assess whether this is evidence of H5 transmission," she said, adding that COVID-19 activity was also high in August and the symptoms were easy to confuse. Michael Osterholm, an infectious disease expert with the University of Minnesota, also said it could be "any number of respiratory illnesses".

The confirmed Missouri case occurred in a patient who was admitted to the hospital with underlying health conditions and was tested for influenza as a part of their workup. It was unclear whether the patient's underlying conditions caused the symptoms or the flu. The Missouri case was the 14th person in the United States to be diagnosed with bird flu this year. The other 13 cases were among farm workers and linked to bird flu outbreaks on poultry or dairy farms.

Bird flu has infected more than 200 dairy herds in 14 states since March, according to US Department of Agriculture data.

(With inputs from agencies.)