US health officials expect more cases of the coronavirus disease, Covid-19, in the coming days and weeks, even though the risk to the general public remains low.

So how will we know where those cases are and how fast the virus is spreading through the population?

The answer is simple: We need diagnostic test kits. A lot of them. And with cases of the disease confirmed in over 50 countries, we also need testing that focuses far beyond people with links to China, where the outbreak originated. While cases are slowly mounting in the US, widespread testing for the new coronavirus is still being rolled out. In many places, testing won’t be up and running until at least next week — even as the Food and Drug Administration rolled out a new policy on Saturday allowing some hospital and academic labs to create and use their own Covid-19 tests, ahead of the agency’s approval.

The problem is testing in the US has been limited so far, with only a small number of labs available to assess the results, flaws in the manufacturing of the earliest kits sent out to states, and out-of-date criteria for testing people. Until Friday, most tests focused on people who’d been to China recently or those with known Covid-19 exposure.

“This has not gone as smoothly as we would have liked,” Nancy Messonnier, director of the Centers for Disease Control and Prevention’s National Center for Immunization and Respiratory Diseases, said of the testing snafus in a Friday press briefing.

The need for change became more urgent this week, when the CDC announced the first coronavirus case in a patient in Northern California with no history of travel to the countries affected and no known exposure to others with the virus. According to a statement from UC Davis Health, where the California patient was diagnosed, “a test was not immediately administered” because the individual “did not fit the existing CDC criteria for COVID-19.”

As of Saturday, the total number of confirmed cases in the US was 62, include 15 cases detected here and the 44 repatriated US citizens who were aboard the Diamond Princess cruise ship and 3 diagnosed in Wuhan. The CDC also announced four more possible — but not yet confirmed — cases late Friday with no known link to China or other Covid-19 patients.

This all means Covid-19 could already be spreading more broadly in the US than we know. Without better and broader diagnostic testing, people may be at risk. Here’s what we know about the state of the diagnostic testing in the US and around the world, and why it’s essential that these shortages are soon fixed.

There have been problems with the CDC’s Covid-19 test kits

The CDC started sending out test kits to laboratories the first week of February, a month after China announced the outbreak. But the health agency quickly encountered a problem.

Some labs reported to the CDC that some of the test kits were delivering inconclusive results during verification. It’s believed that one of the chemicals used to conduct the test was not working properly and needed to be remanufactured.

The tests are conducted via mouth or throat swabs, through the testing of mucus that has been coughed up or fluid from a patient’s trachea. They’re designed to identify the virus’s specific genetic signature, and results currently have to be shipped to labs where they take a day to process.

“I am frustrated — like I know many of you are — that we have had issues with our test,” the CDC’s Messonnier told reporters earlier this week, adding that the CDC is working on modifying the kits and sending out new ones.

The problem, though, did not affect all of the test kits the CDC sent out. The Illinois Department of Public Health, for instance, reports the test kits it received are working. As of Friday, the CDC reported, the issue with the test kit ingredient has been fixed. “Right now, labs can start testing with the existing CDC test kits,” Messonnier said Friday.

So testing can and is being done in the United States. It’s just off to a slow start — even by global standards.

“While South Korea has run more than 35,000 coronavirus tests, the United States has tested only 426 people, not including people who returned on evacuation flights,” the Washington Post reported earlier in the week. As of Friday, only 445 people have been tested for Covid-19 in the US.

Not only were the test kits flawed, but few people qualified for Covid-19 testing

A few other factors stymied US hospitals’ ability to test for the virus.

One is the fact that originally, outside of the CDC, there were only 12 labs in five states that could process the tests. Now, as Health and Human Services Secretary Alex Azar said at a Congressional hearing on Thursday, there are 40 labs that can handle them. A total of 93 labs should be able to process the tests by next week.

Another has to do with the criteria for who is deemed eligible for testing in the first place. Not everyone who presents with Covid-19-like symptoms is being tested. The most common early symptoms are fever and a dry cough.

Originally, the CDC’s test criteria included only people who have traveled to China or who have been in close contact with someone known to have Covid-19.

On Thursday, the agency updated the criteria, calling for the testing of people who have traveled to impacted areas, as well as those with severe symptoms (like pneumonia) who do not have a known source of exposure and aren’t ill with another disease (like the flu). “Our criteria also allows for clinical discretion,” Messonnier said. “There’s no substitute for the astute clinician on the front lines of patient care.”

Two weeks earlier, on February 14, the agency also announced it would start testing for the virus in people who hadn’t returned from China across five US cities — New York, Chicago, Los Angeles, San Francisco, and Seattle. But “that effort has not yet begun,” ProPublica reported, due to the lack of reliable tests.

“We expect the first sites to be doing testing by next week, and [we] hope to be able to rapidly move from six to all 50 states,” Messonnier said.

Meanwhile, New York, at least, has started to make its own coronavirus test kits in the wake of the CDC production errors.

The problem of slow diagnostic testing is not limited to the United States. Testing has been falling short the world over.

Until early February, only two countries in Africa — Senegal and South Africa — had the lab capacity to screen for the disease. While China has had more capacity than the US, with the ability to distribute as many as 1.65 million tests per week, according to the World Health Organization, that’s still been “entirely insufficient,” Lawrence Gostin, director of the O’Neill Institute for National and Global Health Law at Georgetown University, told Vox. “Lack of testing kits has angered doctors and patients in China,” he added, leading them to lean on things like CT scans and lung X-rays to diagnose patients.

Test shipments are still ongoing through WHO regional offices and global hubs. The WHO says it will make 250,000 tests available to 159 laboratories across all WHO regions.

As of February 17, the agency had sent 3,500 testing kits to 34 countries and three regional WHO offices. As it stands, there are still many countries with little or no testing capacity.

Testing shortages put people at risk

There have been a couple of startling examples that demonstrate what these limits on testing mean for public health — and for controlling the outbreak.

First, some people who have the virus may put others at risk while they’re waiting to be tested. This just happened in the US. According to reports in the Davis Enterprise and the New York Times, doctors at the University of California Davis Medical Center suspected Covid-19 disease in a patient who sought medical care last Wednesday.

But the patient was only tested for the virus on Sunday because they did not fit the narrow testing criteria set by the CDC. It remains unclear whether this case has spawned others, but it’s a reminder that limiting diagnostics can lead to the (preventable) spread of the virus and expose health care workers to unnecessary risk, said Peter Hotez, the founding dean of the National School of Tropical Medicine at Baylor College of Medicine. “It’s really hard for frontline health care workers to manage this problem,” he said.

Once one person with the disease is identified, they can be treated in isolation so as not to spread the disease further. Family members and other contacts can be notified and placed under self-quarantine in case they are already infected but have yet to show symptoms. But without adequate testing, that’s not happening.

Second, it’s possible that outbreaks are being missed because health officials simply aren’t looking for them. That’s what happened in Iran.

Just over a week ago, authorities there insisted they had no Covid-19 cases within the country’s borders. As of Friday, the number of confirmed cases in Iran exploded to 270 — and the country now has the second-highest number of deaths (34) outside of China. What this suggests, the WHO said Thursday, is that there are probably many more cases in Iran that have yet to be detected. And that’s already something disease modelers have predicted: In a yet-to-be-published study, researchers found there are likely more than 18,000 cases within Iran’s borders.

We need a point-of-care diagnostic test

Until we have better and faster diagnostics, doctors are still relying on a person’s travel history and assessing their symptoms to decide whether to test for the virus.

But with the disease now spread among nearly 50 countries, travel history is increasingly becoming irrelevant. And symptoms aren’t always the best guide, either.

Covid-19 can look a lot like other respiratory illnesses, including the flu and the common cold. And though it’s a respiratory infection, a recent JAMA article found that patients can first present with symptoms like abdominal pain. This means “we may not be detecting cases that do not present in the classic way with fever and respiratory symptoms,” said William Schaffner, an infectious disease expert at Vanderbilt University. Indeed, in the JAMA study, the patient with abdominal symptoms is thought to have infected more than 10 health care workers.

The best way to get around these risks is with a point-of-care diagnostic test, where health professionals can — on the spot — diagnose patients with the disease. Right now, that’s far from what’s happening in the US, with specimens being sent to the CDC for testing in many cases.

“The biggest worry right now in the US [is] we don’t have a point-of-care diagnostic,” Baylor’s Hotez said. Health care workers “are not going to know what they are dealing with and how to isolate patients.”

The WHO has called the development of point-of-care diagnostics a research priority. And when these tests are developed, they’ll need to be available at a reasonable cost.

In the US, there’s always the risk of people not getting tested due to fear of medical bills. The Miami Herald reported that a man who had traveled to China and developed flu-like symptoms after returning home was charged $3,270 for diagnostic tests at the hospital (it turned out he had the flu). It’s easy to envision a scenario where many sick people avoid getting tested for Covid-19 because they fear what it’ll cost.

“The race is on for [rapid] testing capacity,” Gostin said. “Without it, we are flying in the dark.”