The CDC identified four dairy workers with antibodies for H5N1 who did not experience any symptoms, according to a Nov. 7 CDC telebriefing.
To date, there have been 46 human cases in the U.S., with 25 associated with dairy cows, 21 with poultry, and three from unknown exposure. The threat to the public remains low.
The CDC collaborated with state health departments in Michigan and Colorado to conduct anonymized serosurveys among dairy workers exposed to infected dairy cows. A serosurvey collects and tests blood samples from a defined population to assess the prevalence of antibodies against an infectious pathogen. In this case, the survey aimed to analyze the relationship between infections and symptoms among participants, determine infection rates among dairy farm workers, and identify activities associated with infection.
Between June and August, blood samples were collected from 115 dairy farm workers in Michigan and Colorado who worked on farms where cows had tested positive for bird flu. Samples were collected 15 to 90 days after H5N1 was identified on the farm, and participants were interviewed about their activities, protective measures and whether they had experienced any illnesses since the cows’ bird flu diagnoses.
Eight of the 115 samples (7%) showed antibodies for bird flu. Four of the workers recalled having symptoms, mostly conjunctivitis, while the other four were asymptomatic. All eight were Spanish-speaking workers involved in milking cows or cleaning the milking parlor. None wore respiratory protection, and fewer than half used eye protection.
Based on these findings, the CDC updated three safety recommendations:
- Expand worker testing protocols for bird flu exposure to include asymptomatic workers.
- Recommend Tamiflu for all workers with high-risk exposure to H5N1, regardless of symptoms.
- Increase focus on PPE guidance for workers, especially those involved in high-risk activities or culling operations in milking parlors with sick or infected animals.