In most places in America, it’s not hard to get a Covid-19 test right now. You can walk into a clinic, pharmacy, even your local Wal-Mart, and walk out again, nose swabbed, without too much trouble. Getting the results of your test, on the other hand … well, let’s just say you should be prepared to wait, and wait. And wait.

This is a largely different problem than the testing woes that plagued America’s pandemic response in the early months of March and April. Back then, supply shortages, faulty test kits, and federal regulations limiting testing to only certain kinds of labs hindered widespread availability of tests.

Since then, diagnostics manufacturers have significantly boosted production of the materials required to conduct Covid-19 tests. The federal government moved to require that Covid-19 testing be covered by both public and private insurers. Laboratories dramatically ramped up capacity. Today, the US tests 174 people out of every 100,000, second only to Hong Kong in per capita testing. According to the Covid Tracking Project, the US is testing about 725,000 people per day, up from about 640,000 a month ago.

But as a surge in Covid-19 cases intensified across the south and western US in June and July, demand for tests soared, and the nation’s testing infrastructure buckled. Backlogs at commercial labs left people in some states waiting a week or more to receive results. While the situation is starting to improve, many Americans are still experiencing significant delays. And the longer a potentially-contagious person is forced to wait for test results, the higher the likelihood they’ll unwittingly infect others, potentially setting off new outbreaks and making it much harder for public health agencies to slow the spread of the virus.

According to a new nationwide survey, conducted by a consortium of researchers at Rutgers, Northeastern, Northwestern, and Harvard universities, most people are not getting results within the 24- to 48-hour window recommended by public health experts to aid effective contact tracing. And about 20 percent of those tested, many of them Black and Latinx, are being forced to wait more than five days for test results, effectively rendering them useless. Overall, about 10 percent of surveyed people reported waiting 10 days or more.

“If you’re waiting 10 days or more, you can just throw those results out. They’re not helping anyone,” says Katherine Ognyanova, a network scientist at Rutgers University, and one of the co-authors of the report, which was released Monday. Every week, she and her colleagues push out an online survey to tens of thousands of Americans, distributed across every state and the District of Columbia. They were hearing stories and reading news reports about people waiting weeks to get results, but couldn’t find any systematically-collected data on testing turnaround times.

That’s because Covid-19 tests are conducted by a number of different, disparate entities—including hospitals, public health labs, big commercial labs, and academic centers. How long someone has to wait for test results is determined by a number of factors including where their swab is processed, what kind of demand that facility is facing, and a sorting process that prioritizes certain people—health care workers, hospital patients, known contacts of confirmed cases—into a testing fast lane.

“States are tracking a lot of testing data, but wait times are not something that any of them are reporting,” says David Lazer, a computational social scientist at Northeastern University and co-author of the report. He and his collaborators hoped to use their online questionnaire to provide a snapshot of what Americans are experiencing on the ground.