PCRs, antibodies, antigens and false-negatives: A guide to COVID testing in New Jersey
The lines at coronavirus testing locations in New Jersey rival those at the Motor Vehicle Commission. They start before dawn and last for hours.With the holiday season upon us, public demand has never been greater.
Rising case counts and holiday travel — despite repeated admonitions to stay home — have increased the pressure.
There are many types of tests with different uses — some more accurate than others.
Yet testing by itself is no panacea. As the White House outbreaks of COVID-19 have shown, COVID can spread even with frequent testing. Only in combination with isolation and contact tracing, and accompanied by social distancing and wearing masks, can testing help rein in the pandemic.
As the nation awaits the arrival of a vaccine against COVID-19, New Jersey’s 400 test sites have performed record numbers of tests — 75,000 on a recent day. Bergen New Bridge Medical Center administered 1,400 tests at its drive-thru site on Nov. 20 and Passaic County did more than 1,000 at its mobile test site on Nov. 19.
“We have the resources to continue to not only ensure a full testing regime across the state, but to ramp up testing when hot spots emerge,” Gov. Phil Murphy said. He encouraged anyone who has been in a crowded indoor group setting where masks were not universal — or who has arrived from a state where coronavirus is surging (that would be just about everywhere) — to get tested.
Here’s what the experts say about the different types of tests and their uses.
Which is the best COVID-19 test?
There are two main types of tests — diagnostic tests and antibody tests. If you have symptoms, or if you are asymptomatic but want to know if you could inadvertently spread the disease, get a diagnostic test.
The gold standard for diagnostic tests is a COVID PCR test. PCR stands for polymerase chain reaction, which describes the way the test is processed. This is a molecular test — it looks for fragments of the virus’ genetic material in the test specimen and amplifies them.
The test is very sensitive. Even small amounts of virus will be detected, so it is unlikely to produce a false negative result. But it is more expensive, and it takes longer to produce results.
What is a COVID antigen test?
An antigen test, another type of diagnostic test, produces results more quickly. Some are similar to a pregnancy test or blood-sugar test for diabetics — a line on a strip of paper changes color.
While a positive result in someone with symptoms is considered reliable, these tests have a higher rate of false negatives than PCR tests. They are not as useful when asymptomatic or recently exposed individuals want to determine whether they are infected.
“If you’re concerned about spreading infection to others, then relying upon a rapid test is insufficient,” said Dr. Stanley Weiss, a professor of medicine at the Rutgers New Jersey Medical School and professor of biostatistics and epidemiology at the Rutgers School of Public Health. “If that test is positive, it is very likely that it is a true positive. The problem is, if it is negative, there are many false negative results, and the person does not know their true status.”
Many companies have produced tests that received authorization from the federal Food and Drug Administration since the pandemic began.
“Hundreds of these tests have come out over the last couple of months,” said Professor Zvi Loewy, associate research dean at Touro College of Pharmacy and a Fair Lawn resident. “There is very limited control in terms of the results of these tests and how validated they are.”
What is an antibody test for COVID?
Antibody tests are blood tests that look for evidence that your body has previously fought off a coronavirus infection. They do not indicate if you are currently sick or contagious.
There is “no reason for anyone outside of a research study to have an antibody test, period,” said Weiss.
Antibody tests are useful to public health researchers as they learn what proportion of the population has been infected. They are also used in research on blood plasma from recovered COVID patients, and in vaccine studies to monitor the immune response of clinical trial participants.
What about the COVID tests from the NBA bubble?
New Jersey has been chosen as one of the first five states to receive another type of rapid test from the federal government, Murphy announced on Nov. 12. The test, made by Cue Health, was used successfully in the National Basketball Association’s Florida bubble.
The rapid molecular tests, which use nasal swabs, are as fast as antigen tests but more accurate. They produce results in about 20 minutes, compared to turnaround times of hours or days for standard PCR tests.
The tests have a sensitivity rate of 99%, with a very low occurrence of false negatives. “We expect it to perform better than antigen tests,” said Health Commissioner Judith Persichilli.
Once received, the tests will be deployed immediately to two of the three state-run veterans homes, in Paramus and Menlo Park, where staff outbreaks are currently occurring, Persichilli said.
When to test for COVID for reliable results?
Timing is everything. If you get tested too early after exposure, the virus may not be detected.
If you’ve been in a group where someone came down with the virus, “wait two to three days and then get tested,” said Loewy. “Those few days when you’re waiting, you probably should quarantine.” Other experts recommend four to seven days after possible exposure, to make sure the virus has reached detectable levels.
Researchers say the “optimum time to test is within a 48-hour period prior to onset of symptoms and for the first five or six days after symptom onset,” according to Dr. Karen C. Carroll, director of the division of medical microbiology at Johns Hopkins University School of Medicine.
Remember — test results are a snapshot in time. If you test negative before a trip, you know only that when you left your destination you were virus free. Subsequent activities — at the airport, on a plane, at a highway rest stop — may have exposed you to the virus.
Where can I get a COVID test?
New Jersey’s COVID data hub has a tool to search more than 400 test sites statewide by ZIP code. Find it at: https://covid19.nj.gov/pages/testing#test-sites.
“Testing is available to everyone in New Jersey,” the site says. “Anyone who wants a test can now get one” — in contrast to the shortages of tests during the pandemic’s first wave.
New Jersey health officials also set up free “pop-up” test sites in hot spots around the state every week. This week, they are located in Atlantic, Camden and Hudson counties.
Swab or saliva, what type of specimen is best?
The best is still a nasal-pharyngeal swab — a narrow wand swirled high in the nose, where the nasal cavity and the throat meet. Yes, it’s uncomfortable. You can't do it yourself, and the person doing it needs to be fully protected in case you sneeze or cough.
But it is “the gold standard in getting the right amount of sample from the correct location. … If the result] is negative, you can count on it,” said Loewy.
Other less invasive methods use saliva, or swabs swirled lower in the nose.
The saliva test is more than a spit test. “It’s not as simple as I have some saliva in my mouth, just get rid of it,” said Loewy. Accuracy depends on the volume of saliva. “You need to generate a fair amount for the test.”
What if I test negative for COVID?
You may still have COVID, if the test was faulty or you were tested too early in the course of your infection. If you have symptoms, treat yourself as if you have COVID and quarantine. Consult your doctor about being retested.
Remember, test results represent a specific point in time, and you may have been exposed afterward. Even asymptomatic people with a negative result should continue to exercise caution by wearing masks, staying 6 feet apart from others, and washing hands frequently, experts say.
What happens if I test positive for COVID?
Positive test results are reported to the state Health Department each day by laboratories and hospitals and become part of a state database used by local health departments for contact tracing.
When a local health department learns a person has tested positive, a contact tracer is supposed to call them to ask where they have been, whether they have symptoms, and whether they can safely isolate at home or need someplace else to do so. The tracer asks who the person was in close contact with during the two days before symptoms appeared or, if the person has no symptoms, before the test. Those contacts are then called and asked the same questions and provided information about where they can get tested.
All the information is confidential by law, according to the state Health Department. More information is available at covid19.nj.gov.
What COVID tests are used in NJ nursing homes?
New Jersey has distributed more than 727,000 Abbott BinaxNOW tests from the federal government to long-term-care facilities, as well as hospitals, colleges and schools. More than 44,000 were shipped directly by the federal government to nursing homes and assisted living facilities.
These rapid point-of-service tests give results in 15 minutes and are useful for repeat screening of groups, where quick identification of positive cases can be used to isolate staff or residents and contain the spread of infection. They come in a package the size of a credit card and require a nasal swab.
Murphy says they are “a big weapon in augmenting our already ongoing efforts with health care workers." Nursing home workers are currently tested weekly.
Lindy Washburn is a senior healthcare reporter for NorthJersey.com. To keep up-to-date about how changes in the medical world affect the health of you and your family, please subscribe or activate your digital account today.