The graph below made by ABC7 News' data journalism team shows COVID-19 cases per capita in every Bay Area county. Both Marin and Napa counties show a sharp spike in new cases starting around June 5, 10 days after the Memorial Day holiday.
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"This week we saw a significant uptick in COVID-19 transmission countywide," said Dr. Lisa Santora, Marin County deputy health officer, on Tuesday. The county was seeing about 20 new cases a day on average, she said.
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"Many of these cases are related to Memorial Day activities. Over Memorial Day weekend, we saw residents break from shelter-in-place guidance. After months of feeling cooped up and disconnected, families went on road trips and neighbors gathered, sometimes wearing face covers and sometimes not. Sometimes staying 6 feet apart, and sometimes not."
Napa County public health officials are also blaming the spike on social distancing rule breakers, especially parties and social gatherings of mixed households.
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"We've seen a pattern of multiple family households getting together for various celebrations," said county spokesperson Elizabeth Scott. "We saw one case of someone who attended a graduation party of 40 people."
San Mateo County saw a similar surge starting on June 7. It's now practically tied with San Francisco County for the most COVID-19 cases per capita.
The graph tells a different story in Santa Clara County, where the curve shows a smaller rise in new cases since mid-April.
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Some experts have warned we may see another spike in COVID-19 transmission following large protests against police brutality and the death of George Floyd. We may begin to see the public health effects of those mass gatherings this weekend and early next week, given the virus' two-week incubation period.
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Alameda County has the most known cases in the Bay Area at 4,033. The graph shows a steady rises in COVID-19 cases in Alameda County since the beginning of the outbreak in March.
RELATED: Berkeley epidemiologist 'cautiously concerned' over rise in COVID-19 cases in Alameda County
Los Angeles County still has more cases than every Bay Area County combined. As of Thursday morning, there were 65,822 confirmed cases in Los Angeles County.
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