FILE: An aerial view of San Francisco.

In addition to grappling with a brutal heat wave, Northern Californians are now facing another common enemy: norovirus. The virus is also known colloquially as the stomach flu, but the illness, which is often foodborne, isn’t caused by the influenza virus, and the symptoms manifest much differently.  

According to WastewaterSCAN, traces of the contagious gastrointestinal bug are high in western San Francisco, Marin, Novato, Palo Alto and Sunnyvale, and moderate in Redwood City, San Jose and eastern portions of San Francisco. The health organization monitors traces of several different viruses, including COVID-19, in wastewater treatment facilities throughout the U.S. to give the public a broader idea of when they’re actually circulating.  

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