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California, Nevada likely seeing increase in COVID-19 cases due to Labor Day, officials say

Hospitalizations in California could continue to increase, officials warned.

Some areas of the country are beginning to see an uptick in COVID-19 cases that may be due to Labor Day weekend gatherings, officials said.

"It's been 2 1/2 weeks since Labor Day," Ghaly said. "We're starting to see what we think is attributable to Labor Day."

In particular, case rates, COVID-19-related emergency department visits and new COVID-19 hospitalizations are all showing an uptick and are "areas of concern," Ghaly said.

The health department predicts that there will be an increase in hospitalizations over the next month, going from 2,578 as of Friday to 4,864 by Oct. 25. Flu season adds a new layer of concern in this area, Ghaly said.

"We've never done COVID hospitalizations with flu hospitalizations," he said. "It's really about not letting our guard down as we did earlier in the summer."

The increases also come 3 1/2 weeks since the state started its new reopening plan and five weeks after the fire season began, Ghaly noted, both of which could also be contributing factors.

In Oregon, COVID-19 cases are rising after weeks of steady decline, in part due to Labor Day gatherings, as well as the state's recent wildfires and college students returning to school, according to the Oregon Health Authority. The state reported its single highest number of new COVID-19 cases on Friday, with 457.

Regions of Nebraska and Tennessee have also seen case upticks and outbreaks tied to Labor Day weekend gatherings, according to an internal Federal Emergency Management Agency memo obtained by ABC News Friday night.

In Saunders County, Nebraska, rising cases have been linked to a "large gathering" over the holiday weekend, the memo said, while outbreaks in the southwestern part of the state have also been tied to Labor Day as the "epidemic continues to grow" in Nebraska.

Putnam County in middle Tennessee saw a 157% increase in cases in the past week compared to the previous week, with officials attributing the rise to Labor Day gatherings, as well as nursing facilities and schools, the memo said.

Daily new cases were up about 50% in Washoe County, Nevada, officials said this week, blaming in part Labor Day gatherings. There were nearly 88 new cases per day, compared to the mid-50s last week, District Health Officer Kevin Dick said on Wednesday during the county's weekly COVID-19 update.

"The seven-day rolling average that we have of new cases over the past week has increased significantly," Dick said. "We attribute a number of these cases to people that participated in private gatherings over the Labor Day holiday that are now testing positive for COVID-19."

He also pointed to cases in students at the University of Nevada, Reno, who attended off-campus parties.

"That is of concern," Dick said of the increase in cases. "There is a lot of COVID-19 in the community."

Some areas of the country are cautiously optimistic that they have not seen a Labor Day weekend surge in cases, including Alabama and Charlotte, North Carolina, according to reports. Though health experts warn that increases two weeks after major holidays are "very predictable."

"We saw that with Memorial Day and we saw that with July 4," ABC News Contributor Dr. John Brownstein, chief innovation officer for the Boston Children's Hospital and a professor of epidemiology at Harvard Medical School, said earlier this month.

On May 25, Memorial Day, the national seven-day average of new cases was 21,955. Five weeks later, on June 29, the seven-day average jumped to 40,178, an 83% increase in new cases, according to an ABC analysis of data compiled by the COVID Tracking Project.

A similar pattern occurred just over a month later following the Fourth of July weekend. Just two weeks after July 4, the U.S. hit a record high of 76,842 daily cases, and by July 23, current hospitalizations hit a near-record high of 59,718, according to the COVID Tracking Project data.

Death metrics, which tend to lag behind other COVID-19 data, increased in the weeks following the early summer holidays. On July 4, the seven-day average of deaths stood at 500; on Aug. 12, approximately five weeks after the holiday, there were the most reported COVID-19 deaths this summer, with 1,519, the ABC News analysis found.

ABC News' Josh Margolin and Arielle Mitropoulos contributed to this report.