Researchers in Texas detected H5N1 in wastewater from 10 cities, but the risk to humans is currently low. Ongoing surveillance is critical to monitor any potential changes in the virus that could increase its threat to public health.

Several labs will work with federal health authorities to develop a test for avian influenza, as the number of human cases rise across the country.

An extensive look at wastewater samples taken across the United States from May to July found traces of the H5N1 bird flu popping up -- but only in areas populated by farm animals.

In addition to San Diego, wastewater bird flu detections in California included west Contra Costa County on June 10, Turlock on Sept. 4, southeast San Francisco on June 18 and June 26 and Palo Alto on July 4, July 9 and June 19.