By Deena Beasley and Leah Douglas

(Reuters) – The U.S. Centers for Disease Control and Prevention (CDC) stated that farm workers exposed to birds with flu should be tested for the virus, even without symptoms.

This adjustment aligns with the U.S. Department of Agriculture (USDA), which is also broadening its milk testing for bird flu, reflecting concerns regarding the virus's spread on dairy and poultry farms.

Bird flu has affected nearly 450 dairy farms across 15 states since March, based on USDA data.

CDC officials indicated no evidence of the virus mutating for easier human transmission or person-to-person spread.

Since April, the CDC reported 46 human cases of bird flu, yet farm worker groups argue this may be an undercount due to workers' reluctance to get tested for fear of quarantine repercussions or mild symptom disregards.

Experts warn that as the virus spreads, the risk of human infections increases, potentially leading to a pandemic.

Nirav Shah, CDC's principal deputy director, noted, "There may be individuals who were infected with H5 but who do not recall having symptoms… we need to cast a wider net for testing."

A serological study doing testing on 115 dairy farm workers in Michigan and Colorado revealed that 7% showed signs of prior infection; however, only half had recollections of showing symptoms.

The CDC also advises administering the antiviral drug Tamiflu to workers with high-risk exposure to sick animals and has expanded guidance for protective equipment, including eye protection.

The USDA announced added testing for bulk milk for bird flu after pressures from industry groups concerned about the virus's spread.

For the first time, a pig on an Oregon farm tested positive for bird flu on Oct. 30, alarming virologists as pigs have been implicated in past human pandemics. Following this, another pig on the same farm was also reported positive on Nov. 6.