Federal officials said Thursday that farmworkers exposed to bird flu should be tested for the virus even if they are not showing any symptoms, especially if they were not wearing the proper personal protective equipment.

The recommendation follows the release of a new Morbidity and Mortality Weekly Report conducted by the Centers for Disease Control and Prevention (CDC) showing some dairy workers have been unknowingly infected with the virus.

In the report, officials write that blood tests were taken over the summer from 45 dairy farmworkers in Michigan and 70 farmworkers in Colorado where cows had tested positive for the virus. Results from the blood sample testing show eight of those workers had evidence of a recent H5N1 bird flu infection.

The serum tests were conducted between 47 days and 59 days after the virus had been confirmed in a herd on each farm, the report notes, and most of the workers reported having multiple job tasks like cleaning cow manure, milking cows or moving and hauling cattle.

Those workers who tested positive for the virus all reported having cleaned the room or building where cows are milked and 88 percent reported having milked cows.  

None of the workers whose blood work showed signs of infection said they used respiratory protection when working and only three said they used eye protection, according to the report. Only one of the eight workers reported having close contact with infected cows.

“All eight were Spanish speakers … none wore respiratory protection, and less than half wore eye protection highlighting the need for better tools to support worker protection,” Demetre Daskalakis, head of the CDC’s National Center for Immunization and Respiratory Disease, said during a call with reporters.

Out of the 115 workers, 40 percent said they started to feel sick after bird flu was detected in the cows on the farms where they worked. Out of the eight workers who showed signs of infection in the blood work, only four said they felt sick after being exposed to the infected cows.

The most common bird flu symptoms among those sick workers were red, itchy eyes with discharge, while the other four reported no symptoms at all.  

The data shows that those who are infected with H5N1 may not show symptoms, Nirav Sha, the CDC’s principal deputy director, said during a call with reporters.

“That means that we in public health need to cast a wider net in terms of who is offered a test so that we can identify, treat and isolate those individuals,” he said.  

CDC officials previously recommended that bird flu testing be limited to those who had been exposed to an animal with the virus and were symptomatic like eye redness, fever and cough.   

H5N1 Bird flu was first detected in cows in the United States in late March. Since then, CDC officials said there have been 46 human cases of H5N1 bird flu with all except one of those cases stemming from an ongoing outbreak in dairy cows.  

Most cases have been reported in California, Washington and Colorado. 

The CDC is also now recommending that those exposed to the H5N1 bird flu be offered Tamiflu — a medication that treats influenza — even if they are asymptomatic.