More than 18 million of the most populous U.S. state’s 39 million residents live in counties where rates of increase have put them on a watch list that may eventually require them to roll back reopening efforts, the Reuters analysis shows. Overall, there were 133,489 cases in California by Tuesday, and nearly 4,700 deaths.

Driven in part by increased social gatherings and workplace transmissions, state data updated Tuesday showed rising transmission and hospitalization in nine counties, including populations centers like Los Angeles, Sacramento and Fresno counties, as well as the more rural Tulare and Imperial counties.

“Many of the cases that are showing up in hospitals are linked to gatherings that are taking place in homes – birthday parties and funerals,” said Olivia Kasirye, public health director of Sacramento County.

One cluster in the state capital region was caused by a single traveler: “Someone traveled from another state and came to visit relatives, and then they all started falling sick,” Kasirye said.