Three additional dairy farmworkers in California contracted bird flu, raising the state total to 20 cases and the U.S. tally to 44 people since March, said the Centers for Disease Control on Monday. “To date, person-to-person spread of H5 bird flu has not been identified in the United States” and the risk to the general public remained low, said the agency.
All but one of the human cases, in Missouri, were dairy and poultry workers who were employed on farms with infected animals. Symptoms have been mild, such as conjunctivitis, and none of the farmworkers has been hospitalized. California officials said they expected more infections would be confirmed among people in contact with infected dairy cattle.
Not included in CDC’s count were four probable cases, one in a dairy worker in California and three in poultry workers in Washington state, that were not confirmed by CDC testing.
Research has shown the bird flu virus spreads best through direct contact, so public health officials recommend the use of protective equipment, such as masks, goggles, and gloves by people working with infected or potentially infected animals. “All available data so far suggest sporadic instances of animal-to-human spread,” said the CDC.
The same variant of the bird flu virus that infected chickens at a Washington state farm was responsible for infecting nine workers at the farm, according to genomic testing.
The CDC said tests of birds from a backyard farm in Oregon that also had an infected pig “showed no mutations that caused concerns related to disease severity or adaptability to humans.” It was the first U.S. case of bird flu in swine. “The discovery that an avian influenza A virus has infected a new mammal species is always concerning, especially when the virus is detected in pigs, which are susceptible to influenza viruses circulating in pigs, humans, birds, and other species.” The mixing of flu viruses in hogs was believed to be the cause of the 2009 swine flu pandemic.
California, the No. 1 dairy state, accounted for 233 of the 442 dairy herds infected by the avian flu virus in 15 states, according to a USDA database, which has been modified to list outbreaks in alpacas in Idaho and swine in Oregon as well as dairy cattle.