A member of the health care staff from the Community Health of South Florida, Inc. prepares to test people for the novel coronavirus on March 18, 2020 in Miami, Florida. Testing availability varies widely across the U.S., making it difficult to get ahead of outbreaks.

The United States has surpassed the rest of the world in the number of confirmed cases of COVID-19, with 85,762, as of today (March 27). That came as no surprise to most experts, as it took seven weeks after the first case of the disease was identified in the U.S. for the country to start testing en masse — plenty of time for the SARS-CoV-2 virus to spread, undetected.

Now, 10 weeks after the country's first case, testing in the U.S. is beginning to ramp up significantly, but not uniformly. As of Thursday (March 26), 20 states were only up to a testing rate of 1 per 1,000 people. And six states had tested fewer than 1,000 people. That means it's difficult to know, based on reported numbers alone, how widely the coronavirus is circulating in a given state or community.

"The problem is we haven't had enough tests," said Steffanie Strathdee, the associate dean of Global Health Sciences at the University of California San Diego's Department of Medicine and author of "The Perfect Predator" (Hachette Books, 2019). "There's not even enough tests to test the people who are sick."

Nearly half of all known U.S. coronavirus cases are in New York, which has reported more than 38,977 cases. As of March 26, the state had recorded 103,479 tests, according to The COVID Tracking Project, a nationwide dataset managed by volunteer analysts and journalists. With a population of 19.4 million, that's a testing rate of around 5 tests per 1,000 people, which is the highest testing rate in the country.

Washington state is a distant second, having recorded 34,292 tests for the state's population of about 7.8 million. That's a rate of 4 tests per 1,000 people. In third place is New Mexico, which has run only about 7,800 tests, but that's a rate of 4 tests per 1,000 people (the state's population is just over 2 million).

The two most populous states in the U.S. are California and Texas, with 39 million and 29 million people, respectively. So far, California is testing at a rate of 2 tests per 1,000 residents, but about 57,400 tests are still waiting on results, according to the state's Department of Public Health. Texas is testing at a rate of only 1 test per 1,000 people.

Why is there such a big difference between states?

Testing for SARS-CoV-2 got off to a rough start in the U.S. On Feb. 5, the Centers for Disease Control and Prevention sent diagnostic kits for SARS-CoV-2 to about 100 public-health laboratories across the country. Most of the labs received faulty kits, which meant testing had to continue exclusively at CDC headquarters until the agency could develop and send out replacement kits.

On Feb. 29, the U.S. Food and Drug Administration commissioner announced that the agency would allow local public health and commercial labs to develop and use their own tests for the novel coronavirus. So, now we have a mix of public health labs and commercial labs testing across the country.

Some states have better public health laboratories than others, said Dr. Jeffrey Klausner, an epidemiologist at the University of California Los Angeles Fielding School of Public Health. New York, for example, has some of the best public health institutions in the country. But labs in other parts of the country are far less equipped. "Public-health laboratories were never really capacitated to be on the front lines of a large disease outbreak," Klausner told Live Science.

Here is the March 26 update of US per-state semi-log chart of case density and trends. NY, NJ, LA, and WA continue to have the highest case densities. There are now 14 states higher in case density than Italy on March 9th when their country-wide lock down occurred. pic.twitter.com/i40z3cFAqbMarch 27, 2020

Many states are depending on commercial laboratories to help run the tests, but so far, those labs seem unable to pivot from their normal testing routines, Klausner said. "There are huge delays in commercial labs," he said. "I have patients that have been waiting for over 10 days now. That's not helpful for patient care or public health."

Klausner and his colleagues in Los Angeles were so frustrated and tired of waiting on testing results in their area that they created a new commercial laboratory themselves in just eight days. They're now running over 500 tests a day, and have the capacity to scale up exponentially. "These kinds of high-capacity, high-throughput laboratories need to be replicated in high outbreak areas," he said.

The attitude and priority placed on testing also seems to differ between state governments, Strathdee said. This might be because there are mixed messages coming from the federal level. Not long ago, President Trump downplayed the threat of the novel coronavirus, assuring Americans it was nothing to worry about. "Governors might be using that as an excuse, and they might be in rural states that aren't yet seeing a huge deluge of cases," Strathdee told Live Science. "The 'not here, not us' attitude is prevalent."

Why is testing important?

"Testing and case identification is critical both for patient care and public health to control these local outbreaks," Klausner said. There are other ways to measure an outbreak, such as the number of doctor visits, emergency room visits and admission to the hospital, he said. That's enough to tell epidemiologists that the outbreaks are geographically limited. But the lack of testing has left states unable to implement a strategic approach to containing the outbreaks. "So politicians have had to resort to these massive statewide shutdowns that would not be happening if there was more testing capacity," he said.

In a perfect world, doctors find out who is infected early on, then isolate those patients and trace their contacts and test them, too. But the U.S. isn't anywhere close to being able to do that right now, Strathdee said. Other places, like South Korea and Canada, have done a much better job at this, she said. Health professionals in those countries can use what's called the ring method, where they essentially draw a ring around cases and test everyone inside the ring and figure out who needs to be isolated. Probably the closest the U.S. has come to this was in New Rochelle, New York, where about 1,000 people were asked to self-quarantine after they were traced back to a lawyer in the community who had COVID-19. It's still too soon to tell, but early data suggests that strategy blunted the disease spread, New York Gov. Andrew Cuomo said in his daily briefing on Wednesday (March 25).

In the U.S., testing data isn't being collated by a government agency. Instead, it's been up to volunteer citizens to create open-source platforms like The COVID-19 Tracker Project, to track the data. It's an amazing effort, Strathdee said, but nobody really knows how complete or accurate the data are.

What is clear, though, is that the number of known cases in the U.S. continues to grow at an exponential rate, with no sign of slowing down, she said. Having more testing data will help make decisions once infection rates have slowed and the ring method can be used effectively, but it probably won't help right now.

"There's something to be said for data but then there's observations on the ground where you can tell it's not going to turn around anytime soon," she said. "Why check the weather forecast when you can look outside and see there's a thunderstorm coming?"

Nonetheless, testing rates are now increasing nationwide, and that's promising news for everyone. "We're starting to see signs that people are mobilizing and that people are serious and we're all in this together," Strathdee said. "I'm heartened by that."

Originally published on Live Science.