The U.S. government is fighting to contain and slow down the spread of a new coronavirus that causes an illness called COVID-19. Testing is central to these efforts. Molecular biologist and viral researcher Maureen Ferran answers some basic questions about how these diagnostic tests work – and if there are enough to go around.
Who gets tested for the virus?
Currently, there are two main reasons someone would be tested for the coronavirus: having symptoms or exposure to an infected person.
The main symptoms of COVID-19, the disease caused by the coronavirus SARS-CoV-2, are fever, dry cough and shortness of breath. These look a lot like the flu and the common cold, so it takes a physician to determine if testing for the virus is necessary.
Initially, the Centers for Disease Control and Prevention recommended testing only people with symptoms and who had potentially been exposed to the virus. But to the surprise of public health officials, several of the first people in the U.S. who tested positive for the virus had no obvious exposure. This development suggested that the virus was being transmitted locally, meaning it was spreading from person to person easily and/or that people may have been transmitting the virus without experiencing serious symptoms.
In response, on March 4 the CDC changed its recommendations to allow anyone with COVID-19-like symptoms to be tested as long as a doctor-approved the request. Since the number of available tests is limited, the CDC is encouraging physicians to minimize unnecessary testing and consider a patient’s exposure risks before ordering tests.
As of writing this, there are no specific treatments available for COVID-19, but that does not mean testing is pointless. Perhaps most importantly, testing is done so that infected patients can be quarantined and the spread of the virus slowed. Another benefit of testing is that it lets public health workers build a more accurate picture of the number of cases and how the virus is spreading in the population.
What it is like to get tested?
For a patient, the process of being tested for the virus is easy and can potentially be done almost anywhere. It typically involves taking a swab from deep in a patient’s nasal cavity to collect cells from the back of the nose. The sample is then sent to a lab, where it will be tested to determine if the patient’s cells are infected with the virus. The same process is used to collect a sample from a patient who is tested for flu.
How does the test work?
While collecting a sample is easy, actually determining whether a person is infected with the coronavirus is much more complicated. The current method looks for the virus’s genetic material (RNA) in a patient’s cells.
In order to detect the presence of RNA in the patient’s sample, labs perform a test called reverse-transcription polymerase chain reaction. This method first converts any viral RNA to DNA. Then the DNA is replicated millions of times until there are enough copies to detect using a specialized piece of equipment called a quantitative PCR instrument.
If genetic material from the virus is found in the sample, then the patient is infected with the virus.
It takes 24-72 hours to get the results of a test. During the early ramp-up of testing, there were some concerns about the test’s accuracy after one study found 3% of tests in China came back negative when the samples were actually positive. But this type of genetic test is generally very accurate – more so even than rapid flu tests – and the benefits of testing outweigh the risk of an error.
The Virginia Mercury is a new, nonpartisan, nonprofit news organization covering Virginia government and policy.