The avian flu has reportedly spread to 42 dairy herds across nine states, according to the Centers for Disease Control and Prevention (CDC). Now, concerns are being raised about further spread of the virus to humans.

There have been only two confirmed cases in humans so far. However, the Colorado Department of Health reported on Friday, May 9, that 70 dairy farm workers are being monitored for possible symptoms of the bird flu.

The workers were reportedly exposed to the virus at two dairy farms, however, none of the workers are currently showing symptoms of the disease. The farms with the infected herds have not been identified. The Health Department is coordinating testing and getting antiviral drugs ready in case the workers do test positive.

Experts said the bird flu has likely been circulating in dairy herds for about four months.

“This virus like all viruses, is mutating,” Dr. Robert Califf, the U.S. Food and Drug Agency (FDA) commissioner said on Wednesday, May 7. “We need to continue to prepare for the possibility that it might jump to humans.”

Several epidemiologists criticized the federal government’s response, likening it to the early days of COVID-19 pandemic. Some are reportedly frustrated that more livestock herds aren’t being tested. Others have warned of a lack of transparency regarding the potential spread, noting the dearth of information about how H5N1 is being spread amongst cows.

Testing for the virus in dairy herds was previously voluntary, making it difficult to track the spread of the avian flu.

The FDA maintains that pasteurized milk is safe to drink and products like cottage cheese are safe to eat. However, the FDA said further testing is ongoing.

On Friday, the U.S. Department of Agriculture (USDA) announced $98 million in incentives to farms with infected herds. The money goes to reimbursing farmers for veterinary costs and proper disposal of milk waste infected with the virus.

In addition, the U.S. Department of Health and Human Services (DHHS) says it plans to spend $101 million to treat and prevent the disease. Meanwhile, CDC is reportedly working to understand the risk to humans, offering payment to farm workers who participate in epidemiological studies.

Epidemiologists believe the disease can spread in humans via direct contact with infected animals, entering through the eyes and nose. The agency recommends PPE gear for farm workers.