The Margin: The CDC is now urging Americans to get tested if they must travel for Christmas or Hanukkah — here’s how

“The best thing for Americans to do in the upcoming holiday season is to stay at home and not travel,” Henry Walke, the CDC’s COVID-19 incident manager, said in a press briefing on Wednesday. “Cases are rising. Hospitalizations are increasing, deaths are increasing. We need to try to bend the curve, stop this exponential increase.”

Related:CDC director warns the next three months will be ‘the most difficult’ in public health history

The CDC had also urged Americans to stay home during the recent Thanksgiving holiday weekend, but an estimated 50 million people still journeyed to see their friends and family anyway. Dr. Deborah Birx, coordinator of the White House coronavirus task force, warned afterward that anyone who traveled for Turkey Day should assume that they were exposed to the virus.

“If you’re young and you gathered, you need to be tested about five to 10 days later,” Birx said, referring to those who traveled for Thanksgiving and spent the holiday with a large number of people. “But you need to assume that you’re infected and not go near your grandparents and aunts and others without a mask.”

Read more:U.S. posts record one-day death toll — before the predicted post-Thanksgiving surge

The CDC is now also advising that anyone who does decide to travel for the December holidays should get tested for COVID-19 one to three days before they travel, and then get tested again three to five days after traveling. And anyone who doesn’t get tested should avoid any nonessential activities for 10 days after their trip.

But you could expect to spend hours waiting in line to get tested for the coronavirus this holiday season. Florida recently reported a line of cars 150 deep waiting for COVID-19 testing, while one drive-up site in Illinois is averaging more than 1,000 visitors a day. And these scenes are being played out over and over again across the country as people rush to get tested ahead of the winter holidays. Indeed, the American Clinical Laboratory Association has warned that the surge in test orders means that many labs are facing delays in delivering test results, with Quest DGX, +0.38%  also recently echoing that it expects “turnaround times to grow” as COVID-19 cases surge across the country.

It should be noted that a negative test only proves you weren’t infected with the virus on the day you were tested, however, and someone with a negative result can still contract and spread the virus while traveling, or while spending time with family and friends indoors. This is one reason why the U.S. Centers for Disease Control and Protection (CDC) has strongly urged Americans to stay home for the holidays this year, whether your test comes up negative or not.

Read:Stay home for the holidays or get tested twice, CDC urges

But there is a lot of misinformation and confusion surrounding COVID-19 testing. So MarketWatch has pulled together the most up-to-date information on COVID-19 testing from the CDC, the Food and Drug Administration (FDA) and Johns Hopkins University to highlight what the tests entail, as well as the answers to some of the most common questions about test results.

What you need to know about COVID testing in general

Keep in mind that all COVID-19 tests are new and being given under emergency use authorization by the FDA, which means this information is subject to change.

How many types of COVID tests are there? There are two main types of diagnostic tests for the novel coronavirus SARS-CoV-2 that causes COVID-19. The first are molecular tests — sometimes called viral tests or PCR tests — which are the most accurate. But they are also slower, because they usually require being analyzed by lab technicians. Then there are also antigen tests, which can return results in as fast as 15 minutes, but these rapid tests can be less accurate.

What is PCR testing? So most molecular tests for COVID-19 are polymerase chain reaction (PCR) tests. These entail taking nasal or throat swabs (or occasionally saliva samples), and running them through a machine in a laboratory or a point-of-care (POC) setting, such as a doctor’s office, urgent care center or outpatient clinic. These tests tend to be highly sensitive, and can detect even low levels of viral genetic material in a sample, making them highly accurate.

What is antigen testing? These are the rapid tests. They entail taking nasal or throat swabs, which are then analyzed to detect one or more specific proteins (aka antigens) from a virus particle. This can be done at point-of-care settings like a doctor’s office, and these tests tend to provide results in under an hour. They are more likely to miss an active COVID-19 infection compared to molecular tests, however, which is why your health care provider may also order a molecular/PCR test if your antigen test comes up negative, but you have COVID symptoms.

Neither the molecular/PCR test nor the rapid antigen test can show if you ever had COVID-19 or were infected with the virus that causes COVID-19 in the past. These tests can only tell if you have an active infection.

What is an antibody test? The antibody test on the other hand, aka the serology or blood test, might tell you if you have been infected with COVID-19 in the past. A blood sample is taken via a finger stick or blood draw, and the test checks the blood for antibodies, or the disease-specific proteins that help fight infections. The CDC notes that because it can take your body a few weeks to develop antibodies after you have an infection, an antibody test may not show if you have a current COVID-19 infection. And at this time, researchers do not know whether the presence of antibodies means that you are immune to COVID-19 in the future.

What is pool testing? One way to save time in the molecular/PCR testing process is to combine genetic material from several people’s swabs into one test, or to pool their samples together. If that test is negative, then none of the people whose swabs were included in that pooled batch are likely to have an active COVID-19 infection. But if the pooled test comes back positive, then each individual swab is retested to find the ones that are positive. Pooled testing can save time and test materials, as it allows lab techs to test more staples. But this is only really helpful in areas where most samples are expected to be negative.

Can I take a COVID test at home? There are some at-home collection tests, which are only available by prescription from a doctor, that allow the patient to collect their own sample and send it to a lab for analysis. Some of these entail having a health care provider videochat with the patient to help oversee the collection of the sample. The FDA also just authorized the first at-home rapid COVID-19 test this week, which will also require a prescription. The $50 test, developed by Lucira Health, will require a person to swab themselves and swirl the sample in a vial, which is then placed in a test unit. The results can be read in 30 minutes or less. The tests should become available across the country in spring 2021.

These are some of the most common questions about COVID testing

This information will also continue to be updated as we learn more about the virus. An increase or decrease in the number of confirmed COVID-19 cases and hospitalizations nationally will also impact the answers to some of these questions, such as the length of time it takes to get results back.

Should I get tested for COVID? People who have symptoms of COVID-19, people who have had close contact with an infected person (being within six feet of them for a total of 15 minutes or more) — even if they are asymptomatic — and people who have been asked/referred to get tested by their health care provider or local/state health department should all get tested, the CDC says. The CDC has also launched this Coronavirus Self-Checker tool to help decide when to seek testing and appropriate medical care here. You should be tested within five to 10 days of possible exposure, as Birx noted.

Where can I get tested for COVID? And where can I get a rapid COVID test? The CDC and the FDA recommend visiting your state or local health department’s website for the latest local information about testing, or you can look for a community testing site in your state. You can also call your healthcare provider.

Is COVID testing free? It is supposed to be. Federal law (as described in the Families First Coronavirus Response Act and the Coronavirus Aid, Relief, and Economic Security Act) requires that private insurers, Medicare and Medicaid cover COVID-19 tests without any cost to consumers. This means no copay, coinsurance or need to meet a deductible, Consumer Reports explains, as well as no charge for the testing itself or the related doctor’s appointment. What’s more, Congress also provided funding to support free testing for people without health insurance, although it does not guarantee the uninsured access to no-cost tests.

But there have been numerous cases of people receiving surprise medical bills, sometimes in the hundreds or thousands of dollars, for their supposedly “free” COVID tests. This can be due to mistakes by insurers and health care providers who sometimes enter the wrong billing code, as well as loopholes in the law that stick some insured people who get their tests out-of-network with the bill. Plus, people without health insurance don’t have the same guarantee of free testing as those who do. So protect yourself by talking to your insurer in advance to confirm whether it will cover the COVID-19 test at the place where you plan to get tested. Or check to see whether your state has clinics that offer free tests, regardless of whether you have insurance.

What should I do if I’m charged for a COVID test? If you have insurance and get a bill that you don’t think you owe, don’t pay the bill right away. The Kaiser Family Foundation suggests contacting both your insurer and the health care provider to make sure someone didn’t make a mistake. If that doesn’t work, file an appeal with your insurance company using this free guide from the Patient Advocate Foundation.

How long does it take to get COVID test results? This is the million-dollar question, and unfortunately, there isn’t a clear answer — especially as the number of COVID-19 cases and hospitalizations has spiked over the last several weeks, which has put an increased burden on the labs running the tests. A rapid test can be turned around in 15 minutes, or some people have waited a week or more to get a PCR test back, depending on their location.

The American Clinical Laboratory Association recently warned that its member laboratories are experiencing a “significant increase” in the volume of COVID-19 test orders, and as a result, there could be an increase in the average time to deliver results. Quest Diagnostics also released a statement revealing that the average turnaround time for its COVID-19 molecular testing is now slightly more than two days for all patients, and up to two days for priority patients.

MarketWatch reached out to leading drugstores that offer tests, as well as CityMD, which operates more than 130 urgent care centers across New York, New Jersey and Washington state. CityMD said you can expect to get your rapid test results back in 15 minutes, and the average turnaround time for a PCR test is currently three to four days. Rite Aid RAD, +7.73%  said its tests are returned within two to five days. CVS Health CVS, +2.73%  said that its test results are typically available in three to four days, but may take longer due to the current surge in COVID-19 cases and increased testing demand during the holiday season.

What should I do if my COVID test is positive? The CDC has detailed guidelines here on what to do if you test positive for COVID-19. Most people have mild illness and can recover at home without medical care, but they should isolate themselves from other members (including pets) of their household as much as possible, and they should not go into public spaces except to get medical care. But if symptoms get worse, contact your healthcare provider. And seek emergency medical attention if you experience severe symptoms such as trouble breathing or persistent chest pain.

What should I do if my COVID test is negative? This can either mean that you probably did not have COVID-19 at the time you were tested, or, that your sample was collected too early in your infection. You should keep monitoring yourself for symptoms of COVID-19; if you have symptoms later, you may need to take another COVID-19 test. You should continue to wear a mask in public and practice social distancing and good hand hygiene, as you can still be exposed to COVID-19 after getting a negative test, and then get infected and spread the virus to other people.

This article was originally published on Nov. 23, and has been updated with statements from health officials and the new CDC guidance on holiday travel.