Ongoing occurrence Avian flu has caused mass deaths of poultry and wild birds in the United States and around the world. The virus, known as H5N1, has adapted to mammals over time and has been found in cats, goats and raccoons. At least 170 dairy farms in 13 states in the United States have been infected, and in April health officials confirmed that a dairy worker had contracted the virus from an infected cow, the first time the virus had jumped from a mammal to a human.
Currently, the number of people infected with avian influenza is on the rise. On July 25, the US Centers for Disease Control and Prevention confirmed three new cases of infection, bringing the total number of infected people in the US since April to 13. The infected people were people who had directly handled infected chickens at a poultry farm in Colorado where an outbreak of H5N1 had been reported among chickens. All three people have mild symptoms and have been prescribed the antiviral drug Tamiflu. The CDC says that the risk of H5N1 infection for the general public remains low.
“These cases aren’t surprising at all, given that these people were handling infected poultry,” said Stephen Morse, an epidemiologist at Columbia University in New York. “The good news is, so far, there’s no evidence of person-to-person transmission. If that were to happen, we’d really have to raise our alert level to a red alert level.”
The CDC is investigating whether the Colorado workers were wearing personal protective equipment (PPE) such as gloves, coveralls, footwear, masks and goggles. Historically, most cases of avian flu have occurred in people who didn’t wear recommended PPE, according to the agency.
The new cases come on the heels of another one discovered this month. On July 19, the CDC confirmed that six poultry workers at another facility in Colorado had avian flu. The infected workers had been helping to cull birds infected with H5N1. When the virus is found on a farm, poultry producers are required to cull all of their birds. With the three latest cases, Colorado now has nine confirmed cases of avian flu.
The remaining four cases (one in Texas, two in Michigan, and one in Colorado) are linked to contact with infected dairy cows. The virus likely spread to workers through raw milk. A study published in May found that the virus can remain stable on milking machines for at least an hour, increasing the risk of infection for humans and other animals. However, pasteurizing milk kills the H5N1 virus.
So far this year, all cases in the United States have been mild, but in the past, H5N1 has had a fatality rate of about 50%. From 2003 to 2023, a total of 878 people have tested positive for the virus and 458 deaths have been reported.
The last time H5N1 caused a major outbreak on U.S. chicken farms was in 2015, killing 50.5 million birds. The first human case of avian flu in the U.S. was reported in April 2022 in a worker at a Colorado chicken farm. No further cases have been reported until this year. “Something has changed,” says Annise Loewen, an influenza researcher at Emory University in Atlanta, Georgia. “Whether that’s due to a change in the virus or a change in the transmission pattern can’t be known without more information.”
