by Dr. Paul Han
What the different tests for COVID-19 mean
As the new cases of COVID-19 decrease, and as more people recover from this disease, more people are asking this question: when is it safe to go back to work? After months of being stuck at home and afraid, we all want to resume our normal lives. We want to be able get out of the house, before we all go crazy. We want to see our friends and relatives, go to church, eat at restaurants and socialize in person. But how dangerous is that? Is there a way to know whether it’s safe? Hopefully, in the next few months (maybe by the time this article comes out), we will have a better test to answer this question.
Currently, we have two different types of tests for COVID-19. The first test, which is called the PCR test (for Polymerase Chain Reaction), looks for the presence of the virus itself (by detecting genetic material for the virus). The second test, which is the antibody test, checks for for an immune reaction to COVID-19. This test does is not necessarily positive when someone first gets infected, but can be used to determine if someone had the virus in the past. Based on these tests, we can estimate your risk for getting COVID-19 and/or giving other people COVID-19.
LIKELY SAFE: IgG positive (recovered)
The people that are probably safest, now, are those people that have already recovered from COVID-19 and are immune. If you have had previous illness and have positive antibodies, you probably will not get COVID-19 again, and you probably will not spread the virus to other people. Though physicians currently do not know how long immunity to COVID-19 will last, we have not yet seen anybody who had COVID-19 get the virus again.
The best way to test for immunity is through antibody testing. Unfortunately, the antibody tests that are currently available do not seem to be perfectly accurate. The current test seems to be most helpful for people who were sick enough to be hospitalized, but does not seem to detect antibodies in many people who had mild disease. If you have had a positive COVID-19 PCR test in the past, you do not need antibody testing.
Unfortunately, when recovering from COVID-19, there is no completely accurate test that will determine when you are no longer contagious. The PCR test can stay positive for several weeks during and after recovery, probably due to viral remnants in your body, but that does not mean that you are still contagious. Most studies show that the COVID-19 virus is no longer viable two weeks after the beginning of the illness. The CDC suggests that workers can go back to work if “at least 3 days (72 hours) have passed since recovery defined as resolution of fever, and improvement in respiratory symptoms, and at least 10 days have passed since symptoms first appeared.”
UNSAFE: IgG negative, no symptoms
If you have not had COVID-19, you probably fall into this category. Most people are probably still at risk of catching this disease. Because most people are still susceptible, we must continue to practice social distancing to some degree. These precautions are especially important for people that have risk factors for severe disease: elderly, diabetes, and heart disease.
Unfortunately, the COVID-19 virus is most contagious before patients have symptoms. So anybody without COVID-19 antibodies can also start spreading the virus before they suspect that they are sick. That’s why you need to be careful with everyone if you are not immune.
The only way to detect the asymptomatic spread of COVID-19 is through PCR testing. This testing is being performed in many patients before surgery, and also in some countries or industries prior to close contact. However, a negative PCR is only useful at the moment that it’s done; the results do not mean that tomorrow you won’t catch the virus tomorrow. Also, in some cases, the PCR will be negative even though patients have COVID-19. In fact, despite having COVID-10, the nasopharyngeal swab has been found to be negative in over thirty percent of patients who have the disease in different studies.
DANGEROUS: active disease
Patients who have COVID-19 are obviously in the most danger from having the serious disease and for spreading the disease. COVID-19 can usually be diagnosed based on symptoms. PCR and/or imaging tests such as chest radiograph or CT scan, can be used used to confirm the diagnosis.
Of note, anybody who has been in contact with a positive case can also become contagious and/or develop the disease after an incubation period of up to fourteen days. In general, most (non-immune) people who have had contact with a case of COVID-19 should also remain isolated to prevent the spread of the disease.
Until most people become immune (either through previous illness or through a vaccine), going back to normal life will continue to be risky. As people start to gather more, we need to remember that we still do not have a an effective cure or vaccine for COVID-19. For now, we need to continue to practice social distancing (between workers and customers – 6 ft rule), gloves/masks and cleaning where appropriate. We are now, hopefully, past the worst of the pandemic, but before we can be normal again, we need to be safe.
Paul Han, MD, FCCP
Pulmonary Specialists of North Jersey
Sethuraman, Nandini; Jeremiah, Sundararaj Stanleyraj.
Interpreting Diagnostic Tests for SARS-CoV-2. JAMA:
May 6, 2020.