SAN FRANCISCO (CBS SF) — Early signs of a coronavirus case surge Thursday has health officials in San Francisco warning residents about what is being called an alarming rate of infections and hospitalizations.

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City leaders are trying to prevent a steeper spike in cases after the holiday weekend, once again urging locals to “flatten the curve” with their behavior.

On Thursday, new SF Department of Health figures showed there were six confirmed cases for every 100,000 residents. The city’s goal is to reduce that number to 1.8.

The weekly rate of change in COVID-19 positive hospitalization has spiked to 61 percent, even higher than the 57 percent that led to a similar warning Wednesday. The goal is to keep the hospitalization rate at less than 10 percent.

San Francisco Department of Public Health officials say cases are peaking in minority and economically disadvantaged communities. Many are essential workers.

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A large percentage of cases are attributed to a lack of face coverings and social distancing.

More than half of those diagnosed are asymptomatic.

“Once this virus takes off at a high rate, its very aggressive,” said SF Department of Public Health Director Dr. Grant Colfax. “We need to take this pause now and, as much as possible, stay at home for the Fourth of July.”

Contract tracing has been going fairly well in the city.

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The health department said they’re surveying 82 percent of positive cases and notifying 88 percent of their contacts.