Take-Home Pregnancy Test Debated Over Testing for COVID-19

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The COVID-19 pandemic is relevant to discussions of pregnancy and parenting, not only because of health effects that SARS-CoV2 (the virus that causes COVID-19) may have on pregnant women, the fetus, and the newborn, but also for a plethora of indirect reasons. One such reason is that, as a parent, you may not be able to work, or work as productively or as lucratively as you could prior to stay-at-home situation that has come to characterize many households. In order to return to work, or even to work at home, you may be eager for your children to return to school —in person rather than online— or eager to enroll your toddler or pre-toddler in daycare or preschool. Numerous families, even if they are receiving unemployment compensation (a situation that cannot continue indefinitely for a variety of reasons), would benefit, if both parents could return to full-time work, yet, for many, this would not even be possible, unless the schools also return to a pre-pandemic schedule.

In other posts here on The Pulse, we have discussed progress toward a vaccine, and we are likely to have a COVID-vaccinated population by some point in 2021. That’s a long time to continue in this holding pattern, but experts have been discussing and debating ways to extend testing for the virus on a scale that would allow safe re-opening of schools and an expansion of re-opening of places where people work. If you’re sending children to camp this summer, or if you have children participating in a club sport, dance, or some other activity that stopped for a couple of months and then resumed training, then you know that screening of children consists only of a temperature check upon arrival at the gym, studio, camp, or wherever the kids go. That’s really not so effective, particularly since children are less likely than adults to suffer symptoms if they are carrying the virus, yet they could have a viral load high enough to spread the infection to others.

What we really need to do is to test everybody, including children, who are arriving for any kind of group activity, which certainly includes school. And they must be tested every day, since a child could be negative on Monday due to his viral load being too low to be detected reliably by the test, still negative on Tuesday and Wednesday for the same reason, still negative on Thursday, because the swabbing sample of the nose was just not good, and let’s say positive finally on Friday and Saturday, because the viral load has come up and the swabber obtained a good sample. But there’s a problem, as the gold standard testing method —RT-PCR, which we have discussed in a previous post— is too expensive for school districts, gyms, restaurants, dance studios, and other organizations to test everybody, every day. On top of that, because of a lack of resources and personnel, there are COVID-19 test facilities that have taken as long as two weeks to notify people of their testing results, including positive results. How would you like to be the person making THAT phone call, telling someone that she tested positive two weeks ago?

Just to be very clear: it does not take days or weeks to run RT-PCR and identification of sequences of the SARS-CoV2 virus. If the test kit and someone who knows how to use it are present, a swab sample can be checked in under an hour, but the logistical and personnel issues have been slowing the process.

But this doesn’t happen with the take-home pregnancy test that you may have used to find out you were going to have a child. For many new mothers, they buy a box at the store, open the box at home, and find that the test is much smaller than the packaging. The working part is just a tiny piece of paper, onto which you place a sample of urine and, voilà; if the urine has more than a certain concentration of the pregnancy hormone beta-HCG, there’s a color change, or something shows up in color, creating a plus (+) or something like that. It happens because there is an enzyme on the paper, and the enzyme causes the color change, but only if there is enough of the hormone, because the enzyme is attached to an antibody that attaches to the hormone. Known as an enzyme-linked immunosorbent assay (ELISA), these tests can be mass produced on strips of paper for about $1 each. So when you buy the take-home pregnancy test for $20 at the store, keep in mind that most of that is for the design of the plastic holder around the paper, the packaging, the marketing, the testing and quality control, and also the profit that the manufacturer, store, and middle people make.

Can the same tactic be applied to test for the SARS-CoV2 virus? The answer is yes. In previous posts, we have discussed a different type of antibody, namely testing for the presence of antibodies in people. The idea is that the SARS-CoV2 virus produces an immune response, detectable in those infected by way of antibodies that the immune system makes against proteins present on the surface of viral particles. In the blood, these can be IgM antibodies, which comprise most of the antibodies when you have a new infection, or they can be IgG antibodies, which comprise most of the antibodies when you have been infected a while ago, including when you have been sick and have since recovered. With an ELISA test for the SARS-CoV2 virus, however, we are talking about antibodies present on the paper strip, antibodies that enable the paper to detect proteins from the virus. This test can be performed on a sample of saliva. Like the take-home pregnancy test, it requires no special training, but, instead of peeing on the paper, you spit on it, and the result takes no more than 10 minutes to appear.

Such cheap, fast, paper strip SARS-CoV tests were the topic of a mid-July episode of the podcast This Week in Virology, featuring an interview with Michael Mina, MD PhD, Assistant Professor of Epidemiology at the Harvard University Chan School of Public Health. The discussion highlighted a few key points that Mina and his group of colleagues at Harvard have been emphasizing to government health authorities, based on their research. One point is that, with tests being just $1 dollar each, schools could test each teacher and child every morning. Or, the test could be done at home, at the school bus stop, or at whichever location proves more workable for students and parents. Up to now, the reason why these tests have not been distributed and approved by health authorities is that they are much less sensitive than RT-PCR testing. This means that, to test positive, you need more of a viral load, more viral particles, or more virus in the sample —saliva in this case— for the cheap paper strip testing compared with the gold standard RT-PCR. Consequently, health authorities have been assessing the value of potential new tests based, at least partly, on the viral loads that they can detect in comparison with RT-PCR. The reasoning has been that inferior tests, such as ELISA tests, should be avoided on account of their higher false negative rates, meaning that’ll miss more positive cases.

In the interview, however, another point was that a lot of the positive cases that would be missed by the less sensitive tests are not necessarily cases that would be infectious on that day. The reason is because how infectious you are relates to the viral load, the amount of virus in your saliva or particles in your exhaled air, your coughs, and your sneezes. This, in turn, relates to the concentration of viral particles in your saliva or nose swab sample, which has a major impact on whether or not any kind of test, including RT-PCR, produces a positive result. If a child tests negative on Monday with the $1 paper test and would have tested positive if he had been tested with RT-PCR, it could be that he’s in an early stage of the infection, so his viral load would be rising over the course of the next several days. As the child is tested on Tuesday, Wednesday, Thursday, and so forth at a cost of $1, eventually the paper test would come out positive. Likely, this positive result would appear before the result from the more expensive RT-PCR test would even have become available. Thus, the child would have been going to school day after day anyway. Finally, even if some children are infectious on a day on which they receive negative results (a false negative), they’d surely be just as negative to temperature testing. Considering all of these factors, Mina concluded that use of a cheap, low sensitivity test, day after day, would reveal more infections than use of the better test, since the better test is too expensive to use on everyone and to use every day, and since the results of the better test are not available soon enough.

In the course of the discussion, somebody joked that school children aiming to play hooky would find a way to make the test come out positive, just as kids of past generations figured out how to heat up old-style thermometers. But then someone else pointed out that no, that wouldn’t be wise, since the consequence of of a positive test is that the kid is quarantined for two weeks. And if you kids are like most kids, chances are that they are eager to get back to school and to their other normal activities.

David Warmflash
Dr. David Warmflash is a science communicator and physician with a research background in astrobiology and space medicine. He has completed research fellowships at NASA Johnson Space Center, the University of Pennsylvania, and Brandeis University. Since 2002, he has been collaborating with The Planetary Society on experiments helping us to understand the effects of deep space radiation on life forms, and since 2011 has worked nearly full time in medical writing and science journalism. His focus area includes the emergence of new biotechnologies and their impact on biomedicine, public health, and society.

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