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As tens of millions heed orders to stay at home during the coronavirus pandemic, officials in California are warning people to be beware of what they flush.

In the weeks since the COVID-19 pandemic has spread, officials have discouraged hoarding supplies such as paper towels and toilet paper, which have been flying off the shelves in some stores.

According to market research firm Nielsen, toilet paper sales nationally have jumped about 213 percent in the week ending March 13, compared to the same period a year before.

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Stores such as Costco and Walmart are still getting shipments of toilet paper, but shelves quickly empty out as soon as they're restocked. Smaller retailers and convenience stores have fared better.

But for those running out of toilet paper, turning to alternatives already is having an impact on some communities.

In the Northern California city of Redding, wastewater management officials said Thursday that someone apparently used shredded T-shirts in place of toilet paper, causing a sewer backup.

The soiled T-shirts caused pumps in one of the city's sewer lines to clog at a lift station, which could have led to a dangerous spill, the Record Searchlight reported.

Redding officials said the incident showed why it's important to avoid flushing anything other than toilet paper.

"Clogs in the sewer system can cause fecal matter to back up into showers, toilets and sinks, putting the community at large at risk for another health crisis," the city said in a statement.

Wastewater officials said that if people use anything in the bathroom other than toilet paper, they should, "Bag it. Don't flush it."

Days after that plea, officials in Napa shared what people flushing wet wipes had done to the area's sewer system.

In a Facebook post, the Napa Sanitation District said Monday that a large mound of wet wipes had to be cleaned from a single screen at the district's pump station.

"Please help us keep our sewer system healthy and flowing smoothly," the agency said. "Remember to never flush wipes, paper towels, or tissues because they clog the pipes!"

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The district reminded people to only flush toilet paper and human waste down the toilet, and to throw all wipes and other materials in a trash can.

"We know that wipes are a tricky item- especially with packaging that labels many wipes as 'flushable.' We just want to be sure we clear up any confusion and share that there are no truly flushable wipes," they wrote.

For those who are concerned about toilet paper in the weeks ahead, manufacturers are stressing there is still plenty.

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"We're working around the clock to make sure we can keep delivering products to the retailers as fast as possible,” Loren Fanroy, spokeswoman for Charmin, told the Associated Press.

Most toilet paper sold in the U.S. is made at paper mills in North America, which makes it easier to resupply stores while many foreign-made products suffer from delays and supply bottlenecks, according to the AP.

As of Wednesday morning, California had 2,628 cases of COVID-19 and 54 deaths. California Gov. Gavin Newsom said Tuesday that half of the state's confirmed coronavirus patients are younger than 50.

The Associated Press contributed to this report.