Four new human cases of bird flu were confirmed in the United States by health authorities on Sunday, bringing to eight the number of people infected since the spring by this disease of animal origin.
The infected people are four "farm workers" working on the same poultry farm, the Centers for Disease Control and Prevention (CDC) explained in a press release.
A fifth case is also suspected and must still be analyzed to be confirmed.
The risk to the American population remains "low," however, the CDC stressed. Contaminated workers suffer from "conjunctivitis" and "flu-like symptoms."
An outbreak of bird flu was detected in the United States this spring, with an unusual twist: the disease, which initially mainly affected poultry and birds, is now also affecting cows.
A first infection in Texas, in the southern United States, was announced on April 1. It was then the first known case worldwide of bird flu in a human via a cow.
Two other cases were subsequently reported in Michigan.
And in early July, another case was identified in Colorado on a cattle farm. The western American state is now seeing the disease spread to both livestock and poultry.
Experts are concerned about the growing number of mammals infected with the disease, even though human cases remain rare. They worry that high circulation could facilitate a mutation of the virus that would allow it to jump from one human to another.
The CDC reiterated its call for precautions for workers in contact with infected cows or poultry.
Additional genetic testing is needed on these new cases in Colorado to detect any possible changes in the virus that could lead to "a change in the authorities' assessment of risk" to the population.
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