(Reuters) — Many U.S. dairy farms have not yet increased health protections against bird flu for employees during an outbreak in cows, according to workers, activists and farmers, worrying health experts about the risk for more human infections of a virus with pandemic potential.

Epidemiologists are concerned the virus could potentially spread and cause serious illnesses as farmers downplay the risk to workers while employees are not widely aware of cases in U.S. cattle.

The U.S. government said Wednesday that a second dairy worker contracted bird flu since cattle first tested positive in late March and that investigators are looking into whether the person was wearing or offered protective equipment.

Nearly 24,000 farms sell milk around the country, and they offer varying protections to staff. The National Milk Producers Federation said it encouraged farms to use protective equipment in line with federal recommendations and heard of increased worker protections.

Three dairy workers, seven activists and two lawyers who assist farm employees told Reuters that dairy owners have not offered equipment like face shields and goggles to staff who spend 10- to 12-hour days side-to-side with cows. Three large dairy companies with tens of thousands of cows declined to comment on their procedures.

The workers — all based in New York state, a major dairy producer — said they heard of the new illness affecting cattle through the media or community organizers, not their employers.

The U.S. Centers for Disease Control and Prevention in April and May advised workers to use personal protective equipment (PPE) if they may be exposed to sick livestock, after a Texas dairy worker tested positive for bird flu. On May 6, the agency asked states to make equipment available to workers.

New York state said it is assessing CDC's recommendation and has not yet distributed equipment. Texas, New Mexico and Colorado, where cattle were infected, said they distributed equipment to eight dairies combined. Kansas, Idaho and Wisconsin said they have equipment, but no farmers asked for it.

Michigan, where the second dairy worker tested positive, said many farms have protective gear but the state is coordinating a way to make it available for those that need more.

Dairies became more aware of bird flu's risks in late April after the U.S. government began requiring that cows test negative before crossing state lines, said Emily Yeiser Stepp, who oversees a National Milk Producers Federation program that covers workforce development.

Still, "reaching out into some of our rural networks takes a little longer," she said when told of workers who said they were not informed of recommendations for protective equipment.

The U.S. confirmed bird flu in dairy cattle in nine states. Scientists have said they believe the outbreak is more widespread based on findings of H5N1 particles in about 20% of retail milk samples.

Bird flu has caused serious or fatal infections globally among people in close contact with wild birds or poultry. In cows, the U.S. Department of Agriculture said it believes unpasteurized milk is the primary vector for transmitting the virus, though officials do not know exactly how it spreads.

Health experts advise dairy workers to wear gloves and disposable coveralls that can block milk splashes on their bodies or clothing.