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In response to calls for Covid-19 testing of the entire U.S. population, several large universities, and even some employers, have announced plans for extensive Covid-19 testing of their employees (and students) to support a safe return to work and school. These efforts are based on expert recommendations, some of which call for repeated testing of the entire population (using the PCR test) every 14 days, or even more often. Such initiatives could require millions of tests in the U.S. each and every day.

With each announcement, pressure grows on other organizations — and public health departments — to follow suit, potentially triggering a testing arms race.

While mass Covid-19 testing might seem intuitive, its benefits are unlikely to meet the high expectations for it.

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Proponents of universal Covid-19 testing, meaning testing the entire population, have highlighted its value for contact tracing — a widely touted approach for controlling the spread of an infection by identifying those who had been in contact with an infected individual and quarantining them. Contact tracing has been effective in containing other outbreaks, such as Ebola, and countries such as South Korea and Germany squelched initial Covid-19 outbreaks using aggressive testing and contact tracing.

Frequent testing of the entire population would help identify so-called hidden hidden carriers — individuals infected with SARS-CoV-2, the virus that causes Covid-19, but who have no symptoms of it. They seem to play an important role in the spread of Covid-19. Identifying these silent spreaders could help public health workers be more effective at contract tracing by identifying others who have been exposed and may require quarantine.

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But this argument isn’t as strong as it might seem. Asymptomatic spread is contact tracing’s Achilles’ heel. Even if testing the entire population was able to identify silent carriers, there would be a delay in putting this information to use because testing wouldn’t occur continuously and there would be a lag in test results. This is particularly true since SARS-CoV-2 readily spreads during a short interval of a few days, typically in the early stages of infection. Even with testing every two weeks and a 24-hour lag in results, universal testing would catch less than half of asymptomatic carriers during their most infectious period.

According to a model developed by Imperial College London and the World Health Organization, based on these optimistic assumptions the impact of universal Covid-19 testing would reduce the number of Covid-19 cases by less than 10%. More conservative (and realistic) parameters would suggest a smaller impact.

There are also the harms of Covid-19 testing to consider.

Perhaps the biggest challenge is false negatives — tests signaling no infection in those who are indeed infected. Covid-19 testing is typically performed on samples from behind the nose or in the back of the mouth, and will be positive only if the sample happens to contain the virus. In some people, the virus may be present in high quantities only deep in the lungs. False negatives occur surprisingly often — perhaps as often as one-third of the time — which could lead to a false sense of security among those with such results.

Testing those without symptoms can also lead to false alarms. PCR testing for the virus, which is the best way to identify an active infection, can detect the presence of SARS-CoV-2 — or remnants of it — for weeks, even when the infection is unlikely to be transmitted to others. Testing the entire population would undoubtedly identify a large number of such individuals, unnecessarily sidelining them from work and society.

Other important harms of widespread testing include the real possibility that testing locations might serve as sites for congregation and thus promote the spread of SARS-CoV-2; the need for testers to don scarce personal protective equipment; and the fact that testing is resource intensive, time-consuming, and uncomfortable.

Importantly, not testing the entire population would not represent a nihilistic acknowledgment that Covid-19 cannot be controlled. To the contrary, reducing the focus on testing could enable greater attention on higher-yield efforts. Emerging evidence suggests that consistent use of face masks might substantially reduce infection rates — perhaps by more than 90% (though these findings still require peer review) — based on data from countries like Japan that experienced sustained low infection rates despite limited tracing but regular mask use. In contrast, other nations like South Korea and Germany that suppressed initial outbreaks with aggressive testing and tracing have experienced resurgences after reopening their economies.

In addition to using face masks, meticulous hand-washing, regularly disinfecting surfaces, and continued social distancing could have substantial benefits, particularly for high-risk populations.

I believe that the most important role of testing will be for monitoring Covid-19 within communities to guide the tightening and loosening of social distancing restrictions. During influenza season, the Centers for Disease Control and Prevention regularly conducts such sentinel surveillance to alert health care providers when cases are on the rise. It may even prove there are better ways to conduct sentinel surveillance than testing, such as disease weather maps and wastewater sampling to identify leading indicators of outbreaks.

Though well-intended, when it comes to Covid-19 testing for the entire population, the juice may not be worth the squeeze. We can’t test our way out of this pandemic. Instead, we would get better bangs for our bucks by coupling smart, parsimonious testing with simple, high-value interventions such as face coverings and good hand hygiene.

Michael Hochman is a primary care physician, associate professor of clinical medicine at the Keck School of Medicine of USC, and director of the Gehr Family Center for Health Systems Science and Innovation at Keck.

  • I want people to find out their status. Many will be responsible and take steps to not infect others, BUT:
    1. I have read we do not have enough people to do contact tracing. The claim was, we need 40 times the staff in health departments. We are not going to allow computer spying to do it, and even if we did, without video everywhere, you might know someone traveled but not if they were careful about it.
    2. Knowing who is infected does not stop one infection, DIRECTLY. If a person is not responsible, they will believe they have nothing to fear any longer, and, if they feel healthy, go out and do whatever they want. I am not saying testing has no value, but this is a big limitation.
    3. Contact tracing seems to be something public health people are somewhat irrationally in love with – they have told each other it is a mainstay of infectious disease control forever – everyone involved in public health has probably been taught that as dogma since undergraduate days – but this disease is about twice as contagious as flu – we do not contact trace flu – I know, it is nowhere near as lethal, but the other reason is, you can not keep up with it anyway. In China, which appears to be the biggest surveillance state in the world, they were able to find people in the fronts of buses giving it to people in the backs. All this means, contact tracing will slow this down, but it may be nowhere near as much as some seem to assume.

    What will make a big difference is people wearing masks, and getting the good masks, and even PAPR devices, and using them consistently.

    • Masks are inhuman to wear on a constant basis. We need to see people’s faces. Can you imagine how afraid the deaf will be when they lose the ability to read lips? The fact is I know, because of my behaviour that I am not shedding virus. I will wear a mask when I go into the grocery store to make other people more comfortable but it does little good for me.
      Never would I wear a mask at the beach, hiking a trail or when talking with friends. 6ft apart is a reasonable rule. You can’t eliminate all risk.

    • Jo Weick – I think it is important to remember YOU are not making the rules. I am not making the rules – the government is not making the rules. The virus is making the rules. We can take the strictest most burdensome precautions, or take none at all, but the consequences of our choice will be determined by the virus.
      Sure we can not eliminate risk – and we also can not control the people around us. I can not force you to do what I want, wear the mask everywhere until vaccine day – but, that cuts both ways – the people who want to be super cautious will be, even if you urge them not to be – what will make them stop? In my case, it is very simple – belief I am very unlikely to get sick – and what will make me believe I won’t get sick? Either trust in my own 99.97% PAPR gear, with an airtight helmet and filtered air supplied by hose, or, belief that everyone around me is being so careful, the odds of me getting it are too low to change how I live.
      As long as I get to vote on it, if I see a bunch of people being reckless so that I fear they are going to infect me, I am going to tell my state officials to keep things closed down. If I saw everyone acting as they do in Asia, in the places which got the most travelers from China, in many cases, but now have very low rates, then it makes sense to reopen all the stores and such, with some precautions. Japan, Singapore, South Korea, Taiwan, Hong Kong all never needed a total shutdown, because their people are responsible.

  • I see so much emphasis on testing the broad population.
    The rate of case discovery is so low, it can’t be supported long term.
    It does seem to make sense for people who are exposed to the public or working with vulnerable persons.
    I do feel however, if testing cost can be lowered to say $10 per test and the 5 minute to 15 minute instant tests are widely available, then they have a role in public confidence and returning to normal business transactions. If I knew a restaurant tested their employees every two days, I would seek out that restaurant over another one. Same with a retail shop.
    If everyone had to take such a test before being allowed on a flight, airline business would grow very fast.
    Support masks for now, but I do not want to see that phase go on forever.

  • Like, testing may show that masks significantly reduce infection rates?

    Better to use tests to identify cohorts of workers who have or are likely to fare well with infection who can be united in group work settings.

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