A request for comment from the state’s Wastewater Surveillance Program had not yet been returned.

Although the samples from the Bay Area wastewater sites tested positive for H5, the testing was not specific to H5N1.

However, researchers say a positive genetic identification for H5 is suggestive of bird flu — whether H5N1, the virus that has been found in U.S. dairy cattle (and which has infected three dairy workers ) or H5N2, the subtype implicated in the death of a man from Mexico City this month.

Most human influenza A viruses are of the H1 and H3 variety.

The virus has been detected in 133 dairy herds across 12 states. It has also been found in wild birds and domestic poultry flocks throughout the United States.

In recent weeks, H5 was also detected in wastewater samples in Idaho. among other states.

While there is “no threat to the general public from the H5 detection in wastewater” at this time, said Christine Hahn, Idaho state epidemiologist, “we have determined that it is important that we work to understand these recent findings as much as possible.”

The state is working in conjunction with the Centers for Disease Control and Prevention to investigate the issue.

WastewaterSCAN, the research organization that detected the virus, is an infectious disease monitoring network run by researchers at Stanford, Emory University and Verily, Alphabet Inc.’s life sciences organization.

A review of their data — which samples from 194 locations across the country — suggests H5 has also been detected at sites in Michigan, Texas, Minnesota, South Dakota and Iowa.

California is the only one of these states that has not reported H5N1-infected cattle.

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