It has been one of the chief criticisms of our national response to the COVID-19 pandemic – we need more testing. But what exactly does that mean and will “more testing” provide the answers we seek? Some states and local municipalities are relaxing testing restrictions and making widespread testing available to residents, with or without symptoms. But could this approach actually do more harm than good? And what exactly are we trying to accomplish with more testing? Let’s think about it for a moment.
Antigen Testing
When we hear the word “testing,” more often than not it is referring to diagnostic testing for active COVID-19 infection, aka antigen testing. It is the test to find out whether or not someone currently has COVID-19. It is the test that can be done with a quick nasal swab at a drive-up or walk-up testing site. Until recently, nearly all antigen testing was restricted to people exhibiting symptoms of COVID-19. Many testing sites required a physicians prescription. In the very early stages of the outbreak, only those with symptoms that had either been in contact with a confirmed case or have traveled to China were able to be tested. The exception to all of this has been testing for front line healthcare workers and emergency personnel, who are in regular contact with known or suspected cases.
In the early stages of the outbreak in the US, it made sense to test as many people with symptoms as possible, but we did not have the testing capacity (enough testing kits, trained personnel, testing sites, etc.) at the time. That was a major, and justified, criticism. By identifying as many cases as possible, those who tested positive, especially those with mild symptoms, could be given guidance to self-isolate, as could any others people that may have come into contact with the infected person. The ability to conduct this “contact tracing” has and continues to be a challenge as well.
But there was and remains a major limitation to symptomatic testing – it misses all of the asymptomatic or pre-symptomatic cases, which some suggest could make up more than 50% of all cases (the true number remains unclear). And these asymptomatic cases may have been the “super spreaders” in the early stages of the pandemic before social distancing measures were put in place. One proposed solution to finding asymptomatic carriers is to open testing to anyone, including asymptomatic people. But does this make sense?
Asymptomatic Testing
The problem with widespread asymptomatic testing is that it’s questionable whether it is actually informative for decision-making. An antigen test tells us one thing – do you currently have a COVID-19 infection. If the answer is yes, then that is good news for the health official who can now instruct that patient, and anyone who has been in close contact with that patient, to self-isolate. We can presumably now stop that person from further spreading the virus, whereas otherwise that person may have never even been diagnosed.
But what if that person tests negative? That person may not have the virus at the moment, but could contract the virus later on, be it that day, or that week, or that month. In fact, that person could have been exposed to the virus while waiting to be tested. We wouldn’t know. Thus, a negative test can instill a false sense of security that the person is healthy and safe, when really nothing has changed. A negative test in not especially informative.
Further, it could be a false negative test, meaning that the person has contracted the virus but it may be too early in the infection to accurately detect the virus. This is an even worse case because then that person is likely to spread it to someone else if not practicing strict social isolation guidelines.
Widespread testing can also put a major burden on the healthcare system. It requires trained personnel, personal protective equipment, testing kits, testing sites, and lab equipment. It is worth noting that during the time when testing was restricted only to symptomatic cases, most US states had a positive test rate around 50% or less. With asymptomatic testing, we will have far more negative tests, each requiring the time and resources of the healthcare system. It also has the potential to create a situation that puts healthy people in contact with infected people, while crowding healthcare facility spaces and testing sites.
Asymptomatic testing may make sense in certain situations. Health care workers and first responders who are in daily contact with potentially infected people, should be tested regularly, even in the absence of symptoms. Anyone who has been in recent contact with a known case or a person under investigation (via contact tracing) should also have access to testing without symptoms. Seniors and individuals with underlying health conditions that are at particularly high risk for severe COVID-19 disease could benefit from regular testing (if performed safely). And as we reopen aspects of society, certain types of employees like teachers and day care workers, food service employees, and maybe grocery and retail employees in constant contact with many people, should have access to regular testing.
These represent sectors of the workforce that have the potential to spread the virus widely if infected, but perhaps also represent a more manageable section of the community in terms of size, for which regular testing would be more feasible and practical. How often individuals should be tested is up for debate. But because one test can only tell us whether someone has COVID-19 at that single point in time, the more often the testing the better.
Serologic (Antibody) Testing
Serologic testing, or antibody testing, is the other type of testing that we are hearing about and it may be the type of widespread testing we actually need, though that’s not entirely clear either. Antibody testing looks for the presence of COVID-19 antibodies, which are a signal that the body produced an immune response to a COVID-19 infection. In other words, if you test positive for antibodies, you had the virus.
Based on what we know about viral immunology in general, if your body has produced antibodies to a virus, you have immunity to that virus and cannot be infected again. The problem with the novel coronavirus is that it has been around for less than 6 months and we don’t know for sure if the presence of antibodies means protection from reinfection. It is unclear if you need a certain level of antibodies to achieve immunity. And it is unclear how long that immunity may last. For these reasons, a positive antibody test may not be informative for decision-making about whether it is safe to return to work or relax stay-at-home orders.
It would, on the other hand, help us understand the prevalence of COVID-19 infection in communities, which theoretically could help predict future infection rates. But the latter still requires us to assume that those who have been infected can no longer get or spread the virus in the future.
Currently, antibody testing requires a blood draw (and a trained phlebotomist), which is more invasive and resource intensive than a nasal swap or finger stick. So it is not as easy as testing for active infections. Some commercial labs have made antibody testing available to the general public with and without a doctors prescription, though it is unclear how much these test will cost or if they are covered by health insurance under the CARES Act. More importantly, it is unclear how reliable these tests are. How specific are they to identifying COVID-19 antibodies versus antibodies to other types of cornavirus?
Testing (alone) may not provide all the answers
All in all, antibody testing at this time may not be informative for decision making about when it is safe to return to society. Though it may be the key to safely re-opening communities in the future, should we confirm that the presence of antibodies means immunity. As for widespread asymptomatic antigen testing, it could cause more harm than good, putting a burden on the healthcare system while putting people at risk of exposure, or worse, instilling a false sense of security. And unless we can test nearly everyone, and test everyone on a near weekly basis, and conduct contact tracing on every positive case, then widespread testing just doesn’t make sense.
At the moment, “more testing” alone may not necessarily be the right solution if we cant act on test results. Increased testing has to be done strategically and consistently. It has to be accompanied by the appropriate follow-up including contact tracing and with effective communication to patients about what test results mean and what they don’t mean.