Be 'alert but not alarmed' about bird flu, CDC official urges.

People and public officials should be "alert but not alarmed" about the current bird flu outbreak, federal authorities said in a Thursday call with reporters.

In two new reports, released midday Thursday, officials added details about the spread and status of the outbreak of what is formally called the "highly pathogenic avian influenza." Cattle on more than 90 farms in 12 states have been infected since late last year, as well as three people who caught the disease from cattle. These infections have been widely reported.

"We should take these data we should understand them in context, and we should, as we are, be alert, but not alarmed," Dr. Nirav Shah, the principal deputy director of the Centers for Disease Control and Prevention, said on the call.

Eleven of the impacted farms requested funding from a federal program established to encourage cooperation with public health measures among farmers, officials said.

Farm workers are the only people currently considered at high risk for bird flu, which is not likely to pose a danger to the general public unless it evolves and becomes contagious from person-to-person transmission. Right now the only means of catching the virus is direct exposure to infected animals.

As more animals become infected, however, the risk becomes greater that the virus could mutate and become infectious among people.

To prevent that, "we should apply lessons learned from decreasing farm-to-farm transmission amongst poultry and apply them to dairy farms," Dr. Raj Panjabi, former White House Senior Director for global health security and biodefense, told USA TODAY. Slowing the outbreak of bird flu among poultry under his leadership, federal agencies instituted an approach described as "defend the flock." Now, Panjabi said, we need to "gird the herd."

It is unclear precisely when or how the virus first infected U.S. cattle. The first incidence of the disease was confirmed on a Texas dairy farm on March 25, according to the federal study.

Officials believe the virus was possibly carried from farm to farm on the clothing of workers, 20% of whom work on multiple dairy farms and 7% of whom work on poultry farms as well as at dairies. Other likely routes of transmission include the tires of vehicles used to transport people and equipment from farm to farm. Farms with the infection were linked, the report noted, because the cows were transported between farms and by a milk co-op that is shared by more than 90% of the affected dairies.

Identifying these links should help the government and farmers minimize the spread of the disease, the report concluded.

But the report is far from perfect, said Jennifer Nuzzo an epidemiologist who directs the Pandemic Center at the Brown University School of Public Health. It's more of a survey than an actual study of how the virus is being transmitted ‒ and therefore, it's hard to learn anything from it, she said.

"There are literally no data. They do not know how this is spreading," Nuzzo said.

This lack of data is not the government's fault, she was quick to add. The U.S. Department of Agriculture relies on farms to voluntarily provide information, and, without that data, everyone is in the dark.

"Getting access to information on farms has been challenging, but it's critical for us to understand why this is spreading... so that we can prevent it from spreading," she said. "I don't think there's any one farm that wants to have this. They want to protect themselves. Crucially, I want to protect the workers on those farms."

Panjabi agrees that America won't be safe from bird flu unless farmworkers are protected.

Right now, workers lack access to basic protective gear, he said and wrote in a recent opinion piece. The first worker to become infected had been wearing gloves, but not eye protection ‒ and likely got infected from touching infected hands to eyes.

Farm workers are only tested for infection if they are suspected of being infected, the CDC's Shah said.

Forty-five farmworkers have been tested nationwide for avian flu so far this year, Shah said, including three people who were infected. Of the first 40 tested, 35 were in Michigan, Dr. Natasha Bagdasarian, Michigan's chief medical officer, told the Detroit Free Press.

But it's not realistic to conclude that the only people infected were those who tested positive, Nuzzo said. A positive test requires a farmworker to have access to medical care or be so ill that they have no other options. Then, a caregiver has to be aware of their patient's likely exposure, recognize the potential signs of bird flu and know to send a patient sample to the CDC, she said.

There are "many points of failure," said Nuzzo who would like to see a vaccination begin with farmworkers so they can be protected and officials can prevent further spread. Officials in Finland recently decided to vaccinate farmworkers, veterinarians and scientists who work with avian influenza in that country. "I don't want farmworkers to die before we suddenly decide to vaccinate" people in the U.S., she said.

Eduardo Cuevas contributed to this report.

 Karen Weintraub can be reached at kweintraub@usatoday.com.

This article originally appeared on USA TODAY: Bird flu has spread to dairy farms in 12 states. Data remains thin.