A second Colorado poultry farm has reported a case of bird flu in a worker, marking the state’s seventh human case this month amid an ongoing outbreak among dairy cows.
Colorado health officials said the seventh case is, for now, a presumptive positive. That means the person has tested positive at the state level while confirmatory testing is underway at the Centers for Disease Control and Prevention.
The suspected positive employee worked at a poultry farm in Weld County, in the northeastern part of the state. In recent weeks, six employees at another Weld poultry farm have also tested positive for avian influenza. At that farm, a commercial egg-laying operation with about 1.8 million birds, the employees became infected while slaughtering chickens known to be infected with highly pathogenic avian influenza. Genetic testing of the birds and employees for the virus indicated they were infected with a strain of H5N1 closely related to the virus that is spreading among dairy cows and employees at the dairy farm.
From birds to cows, chickens and humans
The U.S. Department of Agriculture confirmed in late March that the H5N1 avian flu virus, which had been spreading worldwide for years among wild birds, had unexpectedly spread to dairy cows in the United States. To date, at least 168 herds in 13 states have tested positive for the virus. During the dairy outbreak, 11 humans have contracted the virus. Four of the cases have been among dairy workers: one in Texas, two in Michigan, and one in Colorado, which was reported earlier this month. The other seven cases have been among poultry workers, all in Colorado. (A human case of H5N1 was also reported in a Colorado poultry worker in 2022, before the virus spread to cows.)
The recent wave of human infections among Colorado poultry workers is notable given that the H5N1 virus has been raging in poultry flocks across the United States since January 2022. To date, more than 1,000 outbreaks have been documented in 48 states, affecting more than 100 million birds. In most of these cases, poultry, which are highly susceptible to avian influenza, are thought to have been infected directly by wild birds. Yet cases among poultry workers are increasing rapidly, only after the virus jumped from wild birds to dairy cows and then to poultry.
Genetic testing has yet to reveal significant changes in the virus that could explain the recent surge or raise new alarms. There is no evidence of human-to-human transmission, and the CDC still considers the risk of H5N1 to the general public to be low. Additionally, all human cases identified to date have been mild and appear to be responding to flu antivirals. At a news conference last week, federal officials noted that excessive summer heat may be playing a role in the surge in human cases. With temperatures soaring to over 100 degrees Fahrenheit and industrial fans running, Colorado poultry workers culling birds have struggled to keep their masks and goggles in place on their faces.
It’s also unclear how the virus is spreading from dairy farms to poultry farms in this latest phase of the outbreak. Perhaps unsurprisingly, however, Colorado is the state with the most spread from dairy to poultry farms; the state has reported 46 of the nation’s 168 infected herds, the most of the 13 states affected by the outbreak. Weld County, in particular, has reported more than two dozen infected herds.
