A second human case of bird flu has been confirmed in the United States since the virus was first detected in dairy cattle in late March, the U.S. Centers for Disease Control and Prevention said on Wednesday.

The infection of a dairy worker in Michigan expands the outbreak of the bird flu, though the CDC said the risk to the general public remains low.

The CDC told reporters on a call that it has not seen evidence of human to human transmission of bird flu and that it has tested close to 40 people since March, including the Michigan worker.

Michigan and Texas are among nine states that have reported bird flu in dairy herds since late March. Scientists have said they believe the outbreak is more widespread based on U.S. Food and Drug Administration findings of H5N1 particles in about 20% of retail milk samples.