A new study by the Centers for Disease Control and Prevention found that some dairy farm employees showed signs of infection, even when they didn’t report feeling sick. The CDC concluded that more bird flu testing of dairy farm employees is required.
According to Dr. Nirav Shah, the CDC’s principal director, dairy employees who come into close contact with potentially infected animals should be tested and offered treatment even if they show no symptoms.
The new CDC guidance follows a finding that blood tests for 115 farmworkers in Michigan and Colorado showed that eight workers — or 7 percent — had antibodies that indicated previous infection with the bird flu virus known as Type A H5N1 influenza.
“The purpose of these actions is to keep workers safe, to limit the transmission of H5 to humans and to reduce the possibility of the virus changing,” Shah said.
The new CDC study provides the largest window to date into how the bird virus detected last March in dairy cows may be spreading to people.
The study suggests the virus has infected more humans than the 46 farmworkers currently identified in the U.S.. Nearly all were in contact with infected dairy cows or infected poultry.
The study prompting the CDC to take new action is seen as significant. Currently, the CDC recommendations have called for testing and treating workers only when they have symptoms.
The call for more testing testing means the CDC sees the H5N1 viruses as a greater risk than its previous estimates.
The scientific community considers every additional infection in animals or humans a chance for the virus to change in potentially dangerous ways.
CDC’s concern is the virus might spread and jump from species to species.
Of the eight workers in the study with positive blood tests, four reported no symptoms. All eight cleaned milking parlors and none used respiratory protection such as face masks. Three said they used eye protection.
Since April 2024, the CDC has confirmed H5 bird flu infections in 44 people in the United States. Nineteen of these cases were associated with exposure to H5N1 bird flu-infected poultry, and 24 were associated with exposure to sick or infected dairy cows. The CDC reports that the source of the exposure in one case, which Missouri reported on Sept. 6, could not be determined. Serological testing of the contacts of the Missouri case has been reported.
The 44 cases include 20 cases in dairy farm workers in California, three of which were confirmed by CDC last week and three on Monday, November 4; nine cases in poultry farm workers in Washington state, three of which were confirmed by CDC last week; and one case associated with the Washington poultry outbreak that was confirmed by CDC previous week and is pending jurisdiction assignment. Four probable cases are not included in that count- one in a California dairy farm worker and three in Washington state poultry farm workers, which the states have reported.
USDA reports that 440 dairy herds have been infected with the bird flu virus since March, and that number continues to grow.
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