Bird flu found in San Diego County wastewater – San Diego Union-Tribune

San Diego's Point Loma wastewater treatment plant is one of five plants in the state where the H5 influenza virus, often called bird flu, has been detected since May.

The positive result in San Diego came from a sample collected on September 1 by WastewaterSCAN, a private monitoring service run by Stanford University. Subsequent samples collected and tested on September 2 and 8 showed no similar signs.

Similarly, a county program that routinely tests dead birds for a range of pathogens, including avian influenza, has failed to Detection of the virus on site.

Dr. Erik Berg, acting medical director of the county's Division of Epidemiology and Immunization Services, said Monday afternoon that the health alert sent early Monday evening was out of an abundance of caution.

While bird flu can be fatal to humans, those working in agriculture are at much higher risk than the general population.

“The CDC's risk assessment is that the threat to the general population is low, and we agree,” Berg said.

He said it would be a mistake to assume that the virus, which was found in local sewage and whose concentrations were estimated to be low, necessarily came from humans. While sewage systems are designed, built and operated as closed systems, there are ways, such as pipe breaks, that allow entry from the environment.

“We have a closed sewage system so rainwater cannot mix with the sewage. But we all know that's not optimal,” Berg said, adding that viral genetic material was detected in such small amounts that no further tests could be done to determine which type of host might be infected.

Kristian Andersen, a virologist at Scripps Research in San Diego, said in an email Monday that it was an open question why H5 flu viruses appeared sporadically in some samples from municipal wastewater treatment.

“It could be human infections; but it could also be due to people throwing away milk that contains the virus itself or genetic material from it,” Andersen said.

It is clear that this problem extends far beyond San Diego County.

The U.S. Centers for Disease Control and Prevention recently described the virus as “a public health challenge due to a multi-state outbreak of avian influenza virus … in dairy cows, poultry, and other animals.”

The San Diego County Health Department points out in its statement that there have been no cases of bird flu in humans in the region so far and that the dead birds tested for H5 also came back negative.

Why is the county only making the finding public now, more than two weeks after it occurred? Talking to the state and notifying local farms, a county official said, were a priority after local health officials received notification from SCAN on Sept. 9.

While the virus is primarily a problem for cattle and poultry producers, it can be fatal when it spreads to humans. The CDC says it has confirmed 14 cases among 240 people exposed to the virus since March 24.

The CDC recently reported a case of particular concern that occurred in Missouri in a person “with no known occupational exposure to sick or infected animals.” On Friday, September 13, the CDC noted that the other 13 cases identified since April all had documented exposure to animals.

“Four of these cases were associated with contact with sick dairy cows and nine were associated with contact with poultry infected with avian influenza A (H5N1) virus,” the CDC said in a statement.

In addition to San Diego, bird flu was also detected in California sewage in western Contra Costa County on June 10, in Turlock on September 4, in southeastern San Francisco on June 18 and 26, and in Palo Alto on June 4, 9, and 19.