On Monday, eager to know her status and get back to work, she waited at an urgent care center for four hours to get tested. Within minutes, she was told she had tested negative.

Related: CMS updates guidance on cost-sharing for COVID testing and vaccinations

While relieved, Mosterman said the process upset her. "It was incredibly irresponsible for them to promise me a test and have me wait three days to have the test and then to say, 'We don't have it.' That was so frustrating," she said.

As the nation confronts its latest and worsening surge of COVID cases, consumers are again facing delays getting tested, many turning to social media to complain. The problem appears mostly in the South and Midwest, where infections driven by the virus's delta variant are proliferating the fastest.

About 100,000 new cases of COVID are being reported each day this week, up from about 12,000 a day in early July. Testing is up 41% in the past two weeks, to nearly 770,000 tests a day, according to The New York Times' analysis of federal and state data.

Walgreens spokesperson Phil Caruso said the company has seen demand for tests "rise significantly, as testing volume across our stores doubled chainwide from June to July." Overall, Walgreens has met the demand, he said, despite minor delays at some locations.

The shrinking supply of tests becomes clear when checking the websites of the nation's two largest pharmacy chains, CVS and Walgreens — which have become popular test sites since cities and states curtailed testing to focus on vaccinations this spring.

On Wednesday, not a single appointment was available through Friday at 52 Walgreens locations in and around Jacksonville, Florida, which has one of the country's highest infection rates. The earliest option was Thursday morning in Brunswick, Georgia, 70 miles away.

At CVS stores around Jacksonville, tests weren't widely available until Tuesday, nearly one week later, when 21 of the closest 35 stores had appointments. If someone was willing to drive 15 to 20 miles, a handful of slots were available Monday, but nothing sooner.

Jacksonville's Duval County had one public test site open this week, but health officials said they were weighing opening more because of increasing demand.

In Hillsborough County, home to Tampa, officials planned to open testing sites after reports from residents that they were waiting up to three days.

Experts say testing is vital for identifying patients to treat or isolate, as well as for tracking the disease's spread.

"It's understandable that resources have been pulled away, but testing is still a really important part of the pandemic," said Gigi Gronvall, a senior scholar at the Johns Hopkins Bloomberg School of Public Health.

States closed many of their mass test sites over the past several months because of declining demand and the need to focus on vaccination.

Dr. Marcus Plescia, chief medical officer of the Association of State and Territorial Health Officials, said pharmacies likely have an adequate supply of tests, although they may have to redistribute them to keep up with increased demand in hard-hit areas.

"It's no surprise there has been a little bit of a backup," he said.

CVS Health spokesperson Tara Burke said her company is largely keeping up with demand, but she would not comment on consumer complaints about waiting three days or more to have a test.

"We continue to be able to meet the demand for COVID-19 testing, even with increasing numbers of patients seeking out tests at one of our more than 4,800 CVS Pharmacy locations across the country offering testing with same day and future day appointments in most geographies," she said in an email response to KHN.

The nation's largest pharmacies have been popular test sites, although consumers have other options, including going to their doctor, urgent care facilities or outpatient clinics. The tests at all these locations are available at no out-of-pocket expense.

Consumers can also test themselves at home with kits that cost as little as $25 and give results in 20 minutes.

But these tests aren't as accurate as molecular tests analyzed in a lab. Rapid tests come with a higher risk of a false negative result, especially for people without symptoms; that is, the test shows you don't have covid when you actually do.

A spokesperson for Abbott, which makes BinaxNOW, one of the home tests, said the company is working with retailers to meet "increased demand in certain areas of the country as case rates rise, and as testing needs and guidance changes."

Even areas of the country that have not seen huge surges in covid cases have seen appointment slots fill up at the major pharmacies and other testing sites.

In San Diego County, California, on Wednesday, CVS appointments weren't widely available until the weekend, and 13 of 20 Walgreens locations in the city of San Diego had no appointments before Friday.

San Diego County is running walk-up testing sites every day of the week, in addition to locations where appointments are required or recommended. In early July, the county — California's second-most populous — recorded an average of 7,200 tests a day. By the end of the month, it averaged more than 11,800, with more than 15,000 tests on an especially busy day. To meet increasing demand, the county added four new testing locations this week and is working on a fifth, according to Sarah Sweeney, communications officer for the Health and Human Services Agency.

In Sacramento, the county-run sites accept only walk-ins, although some locations are hitting capacity and must refer people elsewhere, a county spokesperson said.

Going to one of the thousands of pharmacies advertising covid testing remains the first option for many people. Yet these days it can be frustrating.

Patricia Rowan said she struggled to find a pharmacy with an available appointment for her 67-year-old mother, Karen Liever. Liever had recently traveled to a conference and wanted to get tested near her home in Palm Bay, Florida, before visiting Rowan, who has young children who are not eligible to be vaccinated.

Rowan finally found a CVS about 25 miles from her mom's home on Thursday.

In Florida, where covid hospitalizations are higher than ever, mass testing sites run by the state closed at the end of May and Gov. Ron DeSantis said local governments could use their CARES Act funding to restart testing operations if they want. DeSantis, a Republican, has spent this week trying to play down the surge in hospitalizations, saying most admissions are of younger adults and death rates are lower than a year ago. He also blamed the rise in cases on unvaccinated immigrants crossing the border illegally into Texas and the Southwest.

"People obviously have the opportunity to get a test," DeSantis said Tuesday, the same day Orlando's main public testing site closed early — for the 16th day in a row — because it had reached capacity. The governor noted that at-home rapid tests are available in pharmacies and criticized the effectiveness of past testing campaigns. "Quite frankly, we spent a lot of money on the testing. … I don't think it did anything to bend the viral curve."

This story was produced by KHN, which publishes California Healthline, an editorially independent service of the California Health Care Foundation.

KHN (Kaiser Health News) is a national newsroom that produces in-depth journalism about health issues. Together with Policy Analysis and Polling, KHN is one of the three major operating programs at KFF (Kaiser Family Foundation). KFF is an endowed nonprofit organization providing information on health issues to the nation. This story can be republished for free (details).

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