For the most part, public health experts across the United States have delivered the same message: Testing is key to tracking and ultimately suppressing the spread of COVID-19.
But some 10 months after the first coronavirus infection was reported in the U.S., there is no clear consensus over exactly how to test for the virus. Since March, the U.S. Food and Drug Administration has approved more than 200 different types of tests for use, according to a statement a spokesperson for the agency provided to The Diamondback.
Various approaches to testing are available in the College Park area and even within the University of Maryland. The Diamondback spoke with several experts to understand the differences between tests and the benefits and drawbacks of each.
There are three types of tests for COVID-19 — polymerase chain reaction (PCR), antigen and antibody — but only PCR and antigen tests can be diagnostic.
Even as students, faculty and staff at this university are required to be tested to be on campus — and as public health officials urge individuals to get tested if they choose to gather with family for the holiday season — it is not clear whether some tests are better than others at detecting the virus before it can be spread.
“Even amongst a group of scientists or experts, there’s a debate about the best use for some of these [tests],” said Dr. Karen Frank, chief of the Department of Laboratory Medicine at the National Institutes of Health Clinical Center. “So, it’s nuanced.”
Antigen tests
Antigen tests, which are also known as rapid diagnostic tests, work by measuring the presence of proteins that are part of the SARS-CoV-2 virus in a sample.
A relatively quick turnaround time is one of the hallmarks of this kind of testing, which is offered at the College Park Medical Center. While results from PCR tests at this urgent care clinic take around 72 hours to be available, results from the antigen test take only around 24 to 48 hours.
Antigen tests tend to be faster than PCR tests due to the expertise required to run both types of tests. While antigen tests do not require trained specialists — allowing for a sample to be quickly run at the same location a sample was collected from — PCR tests involve sending samples to a central laboratory with trained lab staff to operate specialized and expensive equipment, according to Science magazine.
[Here’s how UMD fits into recent COVID-19 testing investigations]
However, Frank cautioned that antigen tests have a lower sensitivity compared to PCR tests, which means they are more likely to have a higher rate of false negatives. While PCR tests can detect a small amount of virus in a sample by making copies of the virus’s genetic material during the test, antigen tests do not have this capability, often requiring a higher amount of the virus to be present to signal that a sample is positive, according to the same Science article.
With sports seasons proceeding amid the ongoing pandemic, basketball and football players at this university are currently getting daily antigen tests. Any athletic team member who tests positive with an antigen test is required to get a confirmatory PCR test, a university spokesperson said in a statement.
In contrast to the PCR tests offered by the University Health Center — which requires samples to be collected from an area of the nose closer to the nostrils — the rapid test offered by the College Park Medical Center requires patients to have a nasopharyngeal swab that goes deep beyond the nostrils.
Where samples are collected affects whether COVID-19 is detected. Research conducted by Drs. James Kirby and Ramy Arnaout of Harvard Medical School demonstrated that deeper nasopharyngeal swabs were better at detecting lower levels of COVID-19 in the samples, but that this benefit was lost using PCR tests that require a large amount of the virus to be present in the original sample to signal that a sample is positive.
PCR tests
Samples collected at the health center are run through a PCR test that is carried out at a lab at the University of Maryland, Baltimore. People in this university’s athletics department who are not associated with either the football or basketball team also receive PCR-based testing.
While PCR tests are highly accurate, there can be bottlenecks returning results due to the limited number of samples that can be run at a single time on the specialized equipment used for these tests. PCR tests continue to be in limited supply in the country since demand is often higher than the availability of labor and specialized materials to run them.
Don Milton, a public health professor at this university, is also using a PCR test for analyzing samples collected from healthy people for an ongoing research study examining the airborne nature of the virus in recently infected people who do or don’t have symptoms.
However, the type of PCR test Milton uses is different from the one used by UMB — he says that while the PCR test his lab uses looks at three different genes in the SARS-CoV-2 virus, the test currently used by the university only looks at two genes.
Milton is also using a technique called “pooling” in his study to conserve testing supplies, meaning that rather than testing one sample at a time, a small amount of several samples are combined and tested at a single time to identify if any of the samples are positive.
[Maryland Gov. Larry Hogan ups police presence statewide to enforce COVID-19 guidelines]
Though this university considered the using the same strategy for samples collected at the health center, campus leadership opted not to pursue this option, said public health professor Neil Sehgal, a member of this university’s health, safety and risk management task force that has been involved in COVID-19 decision-making.
A university spokesperson referred questions about pooling samples collected at the health center to UMB. When asked for comment, a spokesperson for the University of Maryland medical school, which is part of UMB, confirmed that its lab does not pool samples collected at the College Park campus, but declined to comment on whether it had considered pooling samples for asymptomatic surveillance.
Given the variance in COVID-19 testing, there is currently no consistent public health approach for using testing to monitor the spread of the virus. In the meantime, Milton said, “everything is experimental. Nobody knows what the right answers are.”
“To the extent that people are willing to work with us and sign up for our studies, we can help create knowledge that will have a long-term impact,” Milton said.
