Smaller clusters were reported at the Costco locations in Mountain View, Gilroy, Sunnvale and San Jose.
According to Dr. Fenstersheib, the Mountain View location reported four positive cases. The Sunnyvale location reported 13. In San Jose, on Senter Road, there were eight cases of COVID-19. Finally, in Gilroy, six employees tested positive for the virus.
The Santa Clara County Public Health Department says it is working with the stores to investigate the situation.
"The initial investigation shows that most likely it was not inside the store. The cases were most likely infected outside the workplace," said Marty Fenstersheib, Santa Clara County health officer.
Essential workers at Bay Area grocery stores have been hit hard by coronavirus.
A dozen workers at Cardenas Markets in Oakland's Fruitvale neighborhood tested positive for coronavirus in May.
Eight workers at a Trader Joe's in San Jose tested positive for the virus earlier this month.
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