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Recent social gatherings are partly to blame for increased coronavirus transmissions in Riverside and San Bernardino counties, California health officials said.

The counties are among 11 the state is monitoring over concerns about their ability to contain COVID-19 amid reopening plans. 

California public health officials believe the increase in Riverside County is fueled by a general rise in local gatherings, as well as outbreaks at state prisons and skilled nursing facilities and patient transfers from Imperial County.

Riverside County health department spokesman Jose Arballo Jr. said it was always expected that there would be increased coronavirus transmission in the county as more businesses reopened.

And while newly reopened restaurants and businesses meant more people going out and socializing with members of different households, the biggest factor contributing to the increase is families not observing public safety guidelines when they go out, like wearing masks, washing their hands or keeping at least 6 feet away from others, Arballo said.

There were 13,800 confirmed coronavirus cases and 424 deaths in Riverside County as of Monday. That’s up from 9,590 cases and 365 deaths the week before.

Asked about whether health officials are concerned about a potential surge, Arballo said they’re hoping that people start seeing the increased numbers and become more aware of their actions.

He said health officials’ advice hasn’t changed since virus first started spreading, and urged resident to adhere to the safety rules.

California public health officials said another potential source for the spike could be transmission at recent large protests that saw people crowd together without face coverings on.

Arballo said while the protests started off with people not adhering to safety rules, a lot more demonstrators have been wearing masks in recent rallies.

In San Bernardino County, officials reported 9,361 confirmed cases and 234 deaths attributed to the virus Monday — up from 6,593 cases and 225 deaths deaths the week before.

The county is also seeing increased hospitalizations for COVID-19, with 5.5% fewer intensive care hospital beds available from the previous day.

State officials attribute the increase to recent gatherings and more virus transmission at workplaces, state prisons, county jails, hospitals and skilled nursing facilities.

In Ventura County, 16 people tested positive for the coronavirus after attending a neighborhood BBQ party, officials said.

Health officials were made aware of the gathering when county contact tracers noticed that many who tested positive lived in the same area and went to the same event.

“Public Health responded to the area to provide testing and to provide guidance for self quarantine,” officials said.

Gatherings remain prohibited in counties throughout the state.

Gov. Gavin Newsom said Monday that COVID-19  hospitalizations grew 16% over the past two weeks, with a modest uptick in the rate of positive cases — from 4.5% to 4.8% — last week.

“Those that suggest we’re out of the woods, those that suggest this somehow is going to disappear — these numbers tell a very, very different and sobering story,” Newsom said.