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U.S. government officials say a million promised tests for diagnosing coronavirus infections will soon be in the mail. But that still leaves many state and local laboratories without the ability to test for the virus, crucial for curbing its spread around the country.

Some states have developed their owntests. Clinical testing companies are now joining the ranks. LabCorpannounced March 5 that physicians or other authorized health careproviders could already order its test. QuestDiagnostics announced the same day that the company will also offercommercial tests as soon as March 9, pending U.S. Food and Drug Administrationreviews. Participation of those two commercial laboratories could greatlyexpand testing capacity in the United States.

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But for now, we still find ourselves asa country with pretty limited capacity to test, says Michael Mina, anepidemiologist at the Harvard T.H. Chan School of Public Health in Boston.

Heres what you need to know aboutcoronavirus testing in the country.

As of March 6, at least 45 states arenow doing testing for SARS-CoV-2, the virus that causes the disease. Wyoming,Oklahoma, Ohio, West Virginia and Maine as well as Guam, Puerto Rico and theVirgin Islands are listed as in progress of having labs certified to dotesting, according to the U.S. Centers for Disease Control and Prevention. Evenstates that have tests may have only a single kit, containing enough materialto test just 700 people, Mina says.

As of March 5, 1,583 people had beentested at CDC. That figure doesnt include tests now going on in many state orcommercial laboratories, which began this week. Contrast that with the UnitedKingdom, where 20,388 people have been tested as of March 6. Only 163 cases ofCOVID-19 have been detected there. Switzerland, which had 181 cases and onedeath as of March 6, has tested more than 3,500 people.

In the United States, more than 250people in at least 23 states had confirmed cases of the coronavirus diseaseknown as COVID-19, and 14 had died, as of March 6. More cases can be expectedas testing ramps up, experts say.

As more cases are found, healthofficials will need to test contacts of people who carry the virus, and otherill people in affected communities may demand tests, all escalating the needfor more tests.

Vice President Mike Pence told reporters March 5, We dont have enough tests today to meet what we anticipate will be the demand going forward, according to CNN. But having companies tests in the mix could help testing ramp up relatively quickly.

To get a more complete picture of howwidespread the virus is in the United States, were going to needmillions and millions and millions of tests, said Anthony Fauci, directorof the National Institute of Allergy and Infectious Diseases in Bethesda, Md.,during a CNN town hall on March 5.

Health professionals will swab apersons nose or throat, collect phlegm coughed up from the lungs, or squirtliquid into the nose, throat or lungs and collect the liquid again for testing.Neither Quest nor LabCorp will collect such specimens, but doctors or otherhealth providers may send samples to the labs for testing.

Then, those samples are analyzed in a laboratory, where technicians must extract and purify the viruss genetic material from the mucus, cell debris and other stuff in the samples.That sample preparation process is usually the biggest bottleneck [in testing], says Brent C. Satterfield, founder and chief scientific officer of Co-Diagnostics, a company based in Salt Lake City and Gujarat, India, that has developed its own coronavirus test. That test can be used clinically in Europe, but has not yet been approved for use in the United States, although other labs can use components of the companys test to build their own diagnostic tests.

All of the coronavirus tests being usedby public health agencies and private labs around the world start with atechnique called polymerase chain reaction, or PCR, which can detect tinyamounts of a viruss genetic material. SARS-CoV-2, the virus that causesCOVID-19, has RNA as its genetic material. That RNA must first be copied intoDNA. Thats a lengthy part of the process, too, says Satterfield, adding 15to 30 minutes to the test.

After that, the PCR can begin. Theprocess makes millions to billions of copies of selected segments of DNA. Inthe case of the coronavirus, the CDCs original test scanned for three of theviruss genes, but now tests for two. The World Health Organizations test,developed by infectious disease researcher Christian Drosten at the Charit UniversittsmedizinBerlin and colleagues, tests for three genes but is a bit different than theCDC tests. The PCR step typically takes 45 minutes to an hour, Satterfieldsays.

Some assays give instant yes or noreadings, but others may also take time to analyze. All together, it may takeabout three hours to complete a test, Satterfield estimates.

PCR tests are not simple enough to do ina doctors office.

In the United States, a doctor is nowallowed to decide if a test is warranted and collect the sample, but then mustship the sample off for other trained professionals to prepare and test.

Testing was initially limited to onlythose people with symptoms and a travel history to an affected area or contactwith a known case. On March 4, the CDCrelaxed some restrictions on who can get tested. People still haveto be sufficiently sick and have failed a flu test in order to qualify forcoronavirus testing, Mina says.

In some states, the positive test results arecalled presumptive positives until the CDC can confirm them. In those cases,the final official result may take days. LabCorp estimates that it will takethree to four days to return results to physicians.

Many doctors offices can do a rapid influenzatest. But those flu tests dont use PCR, Satterfield says. Instead, they detectproteins on the surface of the influenza virus. While the test is quick andcheap, its also not nearly as sensitive as PCR in picking up infections,especially early on before the virus has a chance to replicate, he says. By theCDCs estimates, rapid influenza tests may miss 50 percent to 70 percent ofcases that PCR can detect. The low sensitivity can lead to many false negativetest results.

Flu tests also arent as specific for aparticular virus strain as PCR is. About 5 percent to 10 percent of the time,flu tests may mistake a different virus for the flu, creating a false positiveresult. Specificity is a big deal when youre testing large numbers of peoplewho arent expected to be positive, Satterfield says. If youre going to testin one of the states that doesnt have a coronavirus outbreak right now, with aspecificity of 90 percent, 10 out of every 100 people are going to show uppositive even though the coronavirus isnt there yet.

Accurate diagnosis is a very highimperative for this [coronavirus], Satterfield says.

An additional benefit of a PCR test isthat it may be able to detect viruses earlier in an infection than a flu-style testcan, he says, perhaps not in the first day, but a couple of days into aninfection when the virus is replicating strongly, but the bodys immune systemhasnt yet begun to fight and produce symptoms. In every infectious disease Iknow of, that is the most contagious period for a person; the point in timewhen the virus has multiplied to its maximum capacity and the body has not yetstarted to rein in on it, Satterfield says. Being able to identify people inthat period and isolate them from others could help curb the spread of thedisease.

Delays started with a manufacturing flawin the CDCs original PCR test, which caused components that detect one of the threetargeted viral genes to not work properly, the health agency says.

Those woes sound like user error to Co-DiagnosticsSatterfield. A lot of what they are seeing is probably due to inconsistent usein the field, he says. Tests that work phenomenally well in the lab, whenthey are sent to the field, sometimes just dont work the same, he says.

Co-Diagnostics test also uses PCR buttests for only one gene versus three. Sometimes the more complexity you havein a test, the more things you have that can go wrong, Satterfield says.

Some delays in getting testing off theground came from emergency measures enacted by the FDA, Satterfield says. Normally,big medical testing labs, such as state health labs and companies like LabCorpand Quest Diagnostics, are allowed to develop and validate their own tests. Butwhen the coronavirus was declareda public health emergency on January 31, labs needed emergencyuse authorization before using their tests to diagnose cases. Eventhe CDC had to get permission to use its test. But on February 29, FDAannounced that labs could devise their own tests and use them clinically whilewaiting for the agency to review their applications. FDA does not intend toobject to the use of these tests for clinical testing while the laboratoriesare pursuing an EUA, the agency saidin a statement.

It looks like there were some prettylarge blunders that led to some serious delays, says Mina, the epidemiologistat Harvard. Instead of reducing the amount of testing at the start of anepidemic we should have been expanding it as quickly as possible and callingfor all hands on deck, he says.

Those delays and the initial limitationson who could be tested may have allowed some cases to slip through the cracksand start community outbreaks in Washington and California.

It will vary from place to place. If you have symptoms of COVID-19 fever, dry cough and often fatigue contact your doctor or local or state health department for more information. Do not go to the emergency room for testing, officials say.

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