Clinical laboratories are now joining the Centers for Disease Control and Prevention (CDC) and the state and local public health labs in testing for SARS-CoV-2, the novel coronavirus that causes the respiratory illness known as COVID-19. Identifying infected individuals through testing will help medical professionals determine who should be isolated and receive care while helping public health officials track the virus' spread.
As testing expands in the U.S., health officials expect a significant increase in the number of people with confirmed cases of COVID-19. However, not all these people will experience severe disease. According to preliminary data, about 80% will have mild to moderate illness. The risk of serious disease increases with age and with having underlying health conditions.
Testing patients has been a challenge for the U.S. healthcare community since the outbreak began in February. A test developed by the CDC received Food and Drug Administration (FDA) approval under the Emergency Use Authorization (EUA) and was distributed to the public health laboratories in the first few weeks of testing. On February 29th, the FDA began allowing hospital and commercial laboratories to use their own tests before those tests undergo FDA review.
As the COVID-19 pandemic continues, the questions of who gets tested, and even how testing is performed and processed, are continually changing. Here are answers to some common questions about COVID-19 testing and the current situation:
What is COVID-19?
COVID-19 is the name of the infection and illness caused by the new strain of coronavirus called SARS-CoV-2. There are seven coronaviruses that are known to infect humans and most cause mild to moderate respiratory symptoms. However, the disease resulting from SARS-CoV-2 infection is similar to MERS (Middle East respiratory syndrome) and SARS (severe acute respiratory syndrome) because it can cause more severe illness, in some cases, lead to pneumonia and death.
Symptoms of COVID-19 may appear 2 to 14 days after exposure to the virus and may include fever, coughing and shortness of breath. Some infected people may be asymptomatic or have no noticeable symptoms and yet be contagious, potentially spreading the virus to others. (For more details, see the earlier news article, U.S. Preparing for More 2019 Novel Coronavirus Cases.)
How is COVID-19 tested?
Most tests to check for COVID-19 rely on RT-PCR (reverse transcriptase polymerase chain reaction) testing to detect the virus's RNA in a respiratory tract sample from a patient. (See below: What type of sample is required for testing?)
- PCR is a laboratory method used for making a very large number of copies of short sections of DNA from a very small sample of DNA so that it can be detected. This process is called "amplifying" the DNA.
- However, because SARS CoV-2 is an RNA virus, and RNA is a single-stranded nucleic acid molecule, it needs to be made into DNA before it can be amplified.
- During the test, an enzyme called Reverse Transcriptase binds to the virus' single-stranded RNA and makes a DNA-based copy that can now be amplified by the usual PCR process.
- If a sufficient amount of viral RNA is present in a sample, it will be amplified and detected, and the test will be positive. If no viral RNA is present, the test will be negative.
The CDC, public health labs, and now some hospital and commercial labs are testing for COVID-19 using RT-PCR, which ideally provides results a few hours after the lab receives the sample. However, not all labs perform this testing and samples may need to be sent to reference laboratories to be processed. In these cases, it may take several days for results.
A recent development that could speed up the testing pace, at least in some areas, is that new rapid tests are being developed by test manufacturers and given emergency-use authorization by the FDA. These testing devices, which also use RT-PCR to detect the virus, can be placed in emergency departments and other hospital spaces, such as intensive care units (ICUs), that have personnel trained to perform the tests. The devices can perform tests one at a time, rather than in batches, and provide faster results.
For example, a new rapid test approved by the FDA on March 18th can produce results in 45 minutes, more than four times faster than previous tests. Another rapid test that received FDA authorization on March 26th can provide positive results in 5 minutes and negative results in 13 minutes. At least initially, these rapid tests will be used only to help triage patients in the hospital and to test healthcare workers.
What type of sample is required for testing?
The preferred sample is a swab from the back of your nose. This is called a nasopharyngeal swab or NP swab. It is collected by having you tip your head back and then a swab (like a long Q-tip with a small head) is gently inserted through one of the nostrils until resistance is met (about two inches). It is left in place for several seconds, then rotated several times and withdrawn. This is not painful, but it may be uncomfortable, cause your eyes to tear, and provoke a coughing spell.
CDC guidance says that other samples from the respiratory tract may be collected when it is not possible to collect an NP swab. These include a swab from the back of the throat (oropharyngeal swab) or a swab from a nostril. Sometimes an NP swab and a throat swab are both collected to increase the chances of getting sufficient virus for the test. Both swabs can be placed in the same tube of transport media and sent to the laboratory for testing.
Who should get tested?
Rules for COVID-19 testing are changing rapidly. On Sunday, March 22, the White House Coronavirus Task Force announced that it is calling on doctors to prioritize testing of hospitalized patients. A key reason for the change in testing guidelines is that the protective gear, such as N95 masks that healthcare workers need to wear when caring for infected patients, is in short supply across the country. Knowing which hospitalized patients have the COVID-19 infection and which do not will allow healthcare workers in that setting to only use protective gear when necessary.
Some hard-hit states, including New York and California, have issued restricted testing guidelines. In California, for example, the governor said that testing should be limited to healthcare workers, people with compromised immune systems, older adults, and other people at high risk.
For the latest details, see the CDC's Priority of Testing Patients with Suspected COVID-19 Infection.
If you think you have been exposed to COVID-19 and develop flu-like symptoms, the current guidance is to assume you have COVID-19 and take precautions, such as separating yourselves from others in your home and calling your doctor for medical advice. You may also try calling your state or local public health department. Not everyone needs to be tested, according to the CDC. Currently there is no treatment, and most people develop mild to moderate illness and can recover at home. The CDC has a Coronavirus Self-Checker that may help inform your decision about getting appropriate medical care.
If you develop serious symptoms, such as shortness of breath, call 911 immediately.
What does the test result mean?
A negative COVID-19 test means that your respiratory symptoms are likely due to something else, such as influenza (flu) or other respiratory viruses. You may be tested for these infections as well to determine whether this is the case. Note that a negative test result means you do not have the infection at the time of the test. You could still become infected later. Also, the RT-PCR tests are very sensitive, but there is a small possibility that you could have a negative result even though you are infected if there is not enough virus in the sample to be detected.
A positive COVID-19 test means it is likely you have been infected with a SARS-CoV-2. However, a positive result can't tell your healthcare practitioner how severe your symptoms are likely to be or how long ago you were infected.
What happens if I test positive?
If you test positive, you need to take several steps to keep the SARS-CoV-2 virus from spreading to others in your home and community:
- Stay home, unless it's to get medical care. Ask others to take care of needs such as grocery shopping.
- Stay away from others in your home and use a separate bathroom if possible.
- Cover coughs and sneezes with a tissue or with your elbow. Wash your hands thoroughly with soap and water, and often.
- Areas and surfaces in your home should be cleaned and disinfected often. The areas where you are isolated should be cleaned every day. (See the CDC’s resource on Cleaning and Disinfection for Households.)
- Stay in touch with your doctor and monitor your symptoms. If your symptoms get worse, call your doctor.
- If you will be visiting your doctor, call ahead first so they can protect others who may not have the virus by giving you a mask and your own area to wait.
- If you have trouble breathing or other severe symptoms, call 911.
More details can be found at the CDC's COVID-19 resource, Caring for Yourself at Home.
Is there a blood (serology) test for COVID-19?
Scientists have recently developed blood tests that detect antibodies produced by the immune system in response to a SARS-CoV-2 infection, but these are not widely available yet. These serology tests detect IgG and IgM antibodies and will be useful in determining who has had COVID-19 in the past even though they might not have noticed any signs or symptoms and/or were not previously tested. These antibody tests also might be useful in determining who may be immune to the infection. However, they likely won’t be useful in diagnosing acutely ill patients because it can take several days for antibodies to develop and be detectable in the blood.