CDC Offers Revised Guidance for Bird Flu Prevention Based on New Study Findings

A new study released by the U.S. Centers for Disease Control and Prevention (CDC) on Nov. 7 found that diary workers infected with bird flu went undetected.

Eight workers tested positive for bird flu antibodies in a sample of 115 Michigan and Colorado dairy farm workers exposed to cows infected with bird flu in a serosurvey, or collection and testing of blood samples. Only four of the eight remembered having symptoms—mostly conjunctivitis—that began prior to or shortly after identification of infected herds.

All eight were Spanish speakers and reported milking cows or cleaning the milking parlor, which are higher risk activities for contracting bird flu. None wore respiratory protection, and less than half wore eye protection, highlighting the need for better tools to support worker protection, the CDC reported. Only one person reported they knowingly worked with bird flu-infected cows. 

In turn, the CDC continues to assess the risk to the general population as low. Efforts to protect people with exposure to animals or animal products affected by bird flu continues to be a key focus of the CDC’s public health activities.

As a result of the findings, the CDC intensified recommendations in three areas to focus on the highest exposure tasks in poultry and dairy operations, ultimately to reduce the risk of infection. Going forward, the CDC is expanding its testing recommendation to include workers who were exposed and who do not have symptoms, particularly those workers who were exposed without having worn proper personal protective equipment (PPE).

“There may be individuals who were infected with H5 [highly pathogenic avian influenza (HPAI) A(H5)], but who do not recall having symptoms,” Dr. Nirav Shah, CDC principal deputy director said. “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.”

“This active case finding reduces the likelihood that a mild infection could turn into a severe infection, or that the infection spreads to anyone else,” he continued. “Simply put, the less room we give this virus to run, the fewer chances it has to cause harm or to change. And the best way to limit the virus’s room to run is to test, identify, treat, and isolate as many cases as possible in humans and as quickly as possible.”

Additionally, the CDC now recommends the use of Tamiflu for exposed, asymptomatic workers who did not protect themselves with adequate PPE. For example, high risk exposure includes a splash of milk in the face from an infected cow or exposure during infected poultry depopulation. Receiving Tamiflu reduces the likelihood of an asymptomatic case being symptomatic, and thus, lowers the risk and the chances of onward transmission to close contacts.

The CDC’s third new recommendation is sharper focus on PPE guidance for workers based on their risk of exposure. The CDC’s PPE recommendations will prioritize the type of PPE a farm worker should wear based on its data indicating which farm tasks present the highest risk for bird flu exposure and infection. The CDC also has developed additional resources to support training workers on PPE use and to explain its role in preventing bird flu from animals infecting humans. 

“The purpose of these actions is to keep workers safe, to limit the transmission of H5N1 to humans, and reduce the possibility of the virus changing,” Shah said.

As of Nov. 6, the CDC has confirmed 46 human cases of bird flu in the U.S. this year. (The CDC will not be including the eight people who tested positive for bird flu antibodies in its totals.) Twenty-five cases are due to the ongoing outbreak in dairy cows, 21 of which are in California. Twenty cases are due to poultry depopulation, including the 11 recent cases from Washington. Additionally, one case in Missouri has been confirmed with no known animal or animal product exposure. As CMM previously reported, on Oct. 29, the U.S. Department of Agriculture National Veterinary Service Laboratories confirmed bird flu-infected pigs was confirmed for the first time. 

The CDC has been working very closely with National Institutes of Health (NIH), particularly its Rapid Acceleration of Diagnostics (RADx) program, to evaluate rapid diagnostic tests that are already available on the market to determine whether those tests are capable of detecting H5. These tests can already detect influenza A, influenza B, sometimes even COVID-19 in general.