To test or not to test? Two experts explain COVID-19 testing

Different countries are pursuing very different strategies when it comes to testing for COVID-19. The WHO supports a policy of widespread testing. But policies around the world vary and there seem to be arguments in support of the different approaches – largely due to supplies, shortages and priorities.

Testing is important because asking people with mild symptoms just to stay home will lead to more infections in the household and community. If tested and positive, people can either be isolated in a facility (like in China/Vietnam) or put on strict home isolation (which they are more likely to adhere to if they know they have the virus for sure). When resources are limited and when the healthcare system is overloaded, however, you don’t want a lot of non-sick people coming to health facilities and risking contagion.

Here, David Duong, MD, MPH - Instructor in Global Health and Social Medicine at Harvard Medical School and Harvard Medical School Director of Global Primary Care and Social Change, as well as a member of the World Economic Forum’s Global Future Council on Health and Healthcare - and his colleague Todd Pollack, MD - Assistant Professor of Medicine at Harvard Medical School and Country Director for the Partnership for Health Advancement in Vietnam, a Harvard Medical School Global Program - explain some of what we know about testing for COVID-19.

What criteria are governments using to test for COVID-19?

Pollack: You see a number of different strategies that depend on a few things. First is the state of the epidemic in the country or community. Second is the availability of testing resources - both the test kits themselves (or the swabs) and personal protective equipment (PPE) for health workers, who are required to wear these in order to take the sample from patients.

Duong: In the US, different states and different cities have different criteria. Some states are testing health care workers who have been in contact with known exposures (people who have tested positive) or who are symptomatic. Or patients with known exposure and symptoms, or people who are immune-compromised and symptomatic.

The guidelines evolve very quickly depending on the availability of testing equipment and supplies of PPE. For example, in New York City, due to supply issues, they have said that as of the 20 March, COVID-19 testing is performed only for hospitalized patients. So they are not doing community testing. Where I practice in Boston, we are still testing non-hospitalized patients, however, you still need approval to get a test. Patients cannot just request a test.

At the beginning of the epidemic, the majority of tests were sent to the CDC for testing. Now, the tests are carried out by the Departments of Health, state laboratories, and in some places, such as at my healthcare organization, we can run our own test, and therefore, increase the amount of testing we can do, and decrease the time patients have to wait for the results.

Pollack: In some countries, for example, South Korea, we've heard a lot about how much testing they're doing and also where I live in Vietnam, where they're scaling up testing. There's less of an issue of lack of supply of test kits and they seem to have less of an issue with PPE shortages. So what we see is that if you have symptoms, you're being tested. If you're a close contact with someone with symptoms, you're also being tested. This is a strategy that is about trying to identify as many people as possible, including asymptomatic people that may have the virus. And then using the results to isolate positive cases and quarantine contacts of those cases to try to slow the spread of the virus.

Duong: If we think about Vietnam from a geographical perspective, it borders China, and yet they have reported very few cases and no deaths so far. When the first cases were imported into the country, the government immediately put protocols in place, and started mobilizing domestic masks, PPE equipment and started looking at diagnostic testing options. They were in a state of containtment, and therefore tested and then isolated positive patients and their contacts. Vietnam mounted a “whole of government” response quite early in the epidemic, closing their borders, and deployed testing and isolation protocols. This strategy allowed them to keep their numbers down and contain the spread.

How do the tests work?

Duong: Most governments and most tests deploy the strategy of what we call real time reverse transcription polymerase chain reaction. This method is the same as how we test for other infections. It compares DNA samples from the suspected person with the DNA sample from the virus. So you need to make sure that you get enough DNA sample to make the comparison.

The preferred way is a swab. The samples are transferred, usually by a health worker to the lab, and the lab runs the tests. Usually multiple tests are run at the same time, which can cause a time delay. So for example, when we were testing at my hospital at the drive-up testing site, we would have people come in and drive up. We'll perform a nasopharyngeal swab of the patient while they are in the car, then the sample goes into a vial. The vial then gets transported to the central lab in the hospital for testing.

What about mass blood testing as a COVID-19 containment strategy?

Pollack: That’s another kind of test. This is the test for the antibody. It doesn't tell you whether you're actively infected with the virus, but it can tell you whether you have been infected previously. So it may be a way for us to tell who has been exposed to the virus and is therefore possibly immune.

We know from studies in cruise ships and other places that probably around 15% of the cases of people who are infected have no symptoms, but you have to be exposed to the virus to develop the antibodies. So when we talk about herd immunity, the idea is that a significant proportion of the population would be exposed to the virus, so that eventually there would not be enough susceptible hosts around for the virus to keep spreading.

But to reach that point, it would be a very large percent of the population. So that would mean that almost everyone would have to be infected. Given how sick it's making people, the consequences of that strategy would mean a lot of people sick, a lot of people in hospitals, hospitals overloaded, and a lot of people dying.

Duong: China and Singapore are currently prioritizing the blood tests. These do not test for the virus DNA like the PCR testing, but rather, the body’s immune response to the virus. "Serological" testing allows us to see who was infected and who wasn't infected, and then how many people were marked with symptoms versus not, that gives a truer scope of the coronavirus epidemic. It also gives us a more accurate mortality rate of this new virus.

Can you get coronavirus again once you’ve had it?

Pollack: We believe that once you're infected, then you would be protected from future infection. We can't say 100% but it’s likely.

It's possible that it could be short lived. There are some respiratory viruses that come around every season, every winter, and people can be infected and then be immune from future infection. However, a year later, that immunity wanes and they're susceptible again. So we don't know right now how long the immunity based on previous infection will last for this virus.

What about mapping its genetic code?

Pollack: Mapping defines the genetic code that makes up the virus. This is helpful for vaccine development. One of the things we want to know is as the virus spreads into hundreds of thousands of people, is it mutating? Is it changing? One of the key features of this category of virus is that as it copies itself, it clones itself. But if it makes a mistake, that's called a mutation. And then that mistake will then be copied in the next cycle.

Those changes can affect the future of the virus. It could make it more or less severe, it can make it last or it could make it evade a vaccine.

So far we haven't seen major changes, which is good news, because it means that if we develop a vaccine, the virus may not be able to mutate to evade it.

What are the latest developments in testing?

Duong: On 27 March, the FDA issued new approval for one rapid test. It's the first rapid test to be given approval for use and it's made by Abbott Diagnostics. The rapid tests can be done anywhere, and results within 15-30 minutes. This is a pretty big game changer. So now we will have to see how quickly it gets deployed, how and where it will be used, and at what price.

So with this new rapid diagnostic test, the sample goes into a box, which they call the platform. It’s a lightweight box, the size of a small toaster oven. And it can sit in a variety of locations. So it is very mobile and immediate.

As of 30 March, for the general population, there is no home testing. All tests need to be administered by a health care provider. However, there is a pilot study going on between Amazon and Seattle, King County.

As we're seeing, I think with a lot in COVID-19, there's a fair amount of innovation coming from the private sector that's working in a very close collaboration with the public sector to get materials and supplies and testing out to the public.