San Diego City Wire

San Diego County has reported the environmental detection of the H5 influenza virus, commonly known as bird flu, becoming the fifth location in California to do so. The detection was made through wastewater testing conducted on September 1, 2024, by WastewaterSCAN, a privately funded operation that monitors wastewater for pathogens at over 150 sites nationwide and 57 sites across California. Subsequent sampling has not detected any virus.

H5 influenza regularly circulates in wild birds and occasionally causes human cases. Recent outbreaks of H5N1 in cattle and a small number of human cases, primarily among farm workers, have brought attention to the virus this year.

The detection in San Diego County does not confirm the presence of a human H5 infection, live H5N1 virus, or the H5N1 B3.13 strain, also known as “Cattle Clade,” which is currently circulating in cattle and occasionally causing human disease among farm workers.

H5 is also regularly detected in states with infected dairy herds such as Colorado, Michigan, and Texas. No detections of the H5 influenza virus have occurred in San Diego County cattle, birds or humans in 2024. There were wild bird detections in 2022 and 2023, and a poultry flock was infected in 2022.

County Public Health Services conducts surveillance of human influenza cases year-round and receives information about lab-confirmed case reports, hospitalizations and deaths. Additionally, the Public Health Lab collaborates with a network of regional labs to perform advanced testing to identify novel strains that might be emerging or flu viruses that may not be well matched with the annual flu vaccine. Regular surveillance updates on major respiratory viruses including Influenza, COVID-19 and Respiratory Syncytial Virus (RSV) are available online.

“San Diego County has a robust flu surveillance system,” said Dr. Ankita Kadakia, County interim public health officer. “While we have no evidence of the virus in people or animals, it is important to be transparent with the public both about the detection status and that we are vigilant and working with our partners at the California Department of Public Health, California Department of Food and Agriculture, and California Department of Fish and Wildlife to monitor for signs of H5 presence locally.”

San Diego County has a closed sewage system where stormwater and wastewater do not intentionally intermix. This greatly reduces but does not eliminate the probability that this detection is from an environmental source such as migrating birds.

The virus may have been introduced into wastewater by discarding contaminated animal products, infected wild bird droppings entering the sewage system or through human or animal infection.

More information about H5 can be found on the Public Health Services website.

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