Testing 101: How Mass Rapid Testing Works, Part 1

I will first offer some examples of how rapid testing could be used at home, in the workplace, and in our communities. From there, I will take a broader perspective to suggest how these layers of testing could be combined into a program capable of suppressing national-level outbreaks without resorting to civilian-level restrictions.

Rapid Testing At Home and At Work

Let’s take a family of four, where both parents work. The kids each take a rapid test in the morning before they go to school. If the result is positive, everyone stays at home until they can take a PCR test to clarify their status (it’s early in the morning, so a same day PCR result would be possible).

If the result is negative, the kids head to school with the rest of their classmates, who have also tested negative that morning. If the kids can’t do a rapid test at home, then the school can provide one. If neither the family nor the school can provide a test, that’s unfortunate, but it’s not the end of the world, as this measure does not need 100% adherence to be effective.

Mum and dad also test themselves and under the same conditions. If their employers have made the sensible decision to provide testing for all employees, they could take the test when they arrive at work. Either way, a positive result would again lead to isolation until a PCR test can be completed. While they wait for that result, a precautionary contact tracing process could begin, as both employers and staff will know who is most likely to be at risk of infection.

A negative result from a single rapid test will never provide conclusive evidence that the individual is uninfected, but a series of negative results from tests performed every day or two will get them pretty close. There is a multiplicative effect at play, and it works in our favour. The probability that an individual rapid test produces a false negative may be 40%, but as the test is repeated day after day, the probability that all of the tests have produced false negatives falls from 40% on the first day to 16% on the second (40% * 40%), then 6.4% and 2.5% on the third and fourth.

This repeated, high-volume testing strategy is called ‘serial testing’ and it can transform a mediocre test into a powerful testing regimen which provides higher levels of confidence as the series continues.

Rapid Testing in The Community

Let’s say it’s your friend’s birthday this weekend and she has invited you over to her place to celebrate. If 10 people were to get together for a house party and one of them came with the virus, there’s a good chance that all 10 would be leaving with it. A large transmission event like this would have the potential to set off further clusters and then community transmission – even if the contacts were traced correctly.

Fortunately, it is another risk that is can be managed with serial testing.

If each member of the group had been testing themselves daily over the preceding week (with the same 60% sensitive test) the probability that a hidden infection managed to sneak into the party would be less than 1%. Most rapid tests have a higher sensitivity, so the risk would be lower still, but in any case, a risk control measure offering anything like 99% effectiveness should not be on the margins of a nation’s policy response.

Perhaps your friend would prefer to celebrate her birthday as a restaurant instead. In that case, your party would take a test on arrival, and you’d wait for your results in a plush outdoor seating area with a complimentary aperitif. This ‘entrance testing’ won’t find every ‘PCR-positive’ infection, but that’s OK because that’s not what it’s designed to do.

We know that most infections are generated by a small percentage of highly infectious individuals. We also know that antigen testing is very good at identifying those individuals, as the test technology is very sensitive to samples with high viral loads. The goal of entrance testing then, is not to find every infection, but to find the most infectious cases so that we can minimise the risk of super-spreader events. If the restaurant can add some social distancing and good ventilation and air filtration, it will create a multi-layered protective system that will greatly reduce the risk of infection, giving confidence to staff and patrons alike.

Entrance testing can be used in any venue where visitors are likely to stay long enough to justify the wait, so cinemas, concerts, museums, sports clubs, gyms, or beauty salons would all be candidates. The risk of the activity or the setting should not distract from the value of the measure – entrance testing can lower the risk of super-spreader events, but it will also add an extra layer of protection wherever it is in effect.

Bringing It All Together

These examples demonstrate the range of options available to policymakers, the ease with which rapid testing could be implemented in society, and the additional protection that these strategies could provide.

Serial testing in schools, households and workplaces acts as an early warning system, finding infections in the absence of symptoms. Entrance testing in community settings identifies the most infectious cases and removes them from the population to prevent super-spreader events. When combined, these measures would reduce risk across much of our society, giving people clarity over their own health status, but also those of their family, friends and colleagues. For many, this would lift the fear and uncertainty clouding their lives.

If the government was then to offer free tests at pharmacies, walk-in centres and drive-through facilities, and to ensure that there were plentiful supplies of rapid tests in every supermarket, newsagent and petrol station, it could create a society in which testing was available to everyone, everywhere, on demand. There would be no need for appointments or advanced planning, and no risk of hours lost to queues. Through their normal day to day activities, the people would receive real time updates on their health and, if needed, they could take action immediately.

You can think of this mass rapid testing program as being like a national sprinkler system, with testing capacity distributed across the country, and continuously deployed to keep local clusters suppressed and prevent national-level waves of transmission taking hold. If we left the sprinkler system on long enough, it might even extinguish all the flames. And then we could turn it off.

But even if it didn’t, mass rapid testing wouldn’t need to completely eliminate transmission for it to work. We just need it to lower the risk across the nation, and to a level for which there would be no justification for restrictions on any social or commercial activities. At that point we would spark a virtuous cycle in which the people would have the clarity to plan their affairs again, household, corporate, and national finances would stabilise, and society could coalesce and normalise once again.

All of this would be possible while providing a much higher level of health protection to everyone (no need to defer appointments or elective procedures in this scenario) and returning control over those health outcomes to the people. That means no more arguments over vaccines, as there would be no need for the vaccines themselves.

A national rapid testing program certainly sounds more attractive than Ireland’s national lockdown strategy, but many ideas sound good in theory, only to disappoint in practice. Could mass rapid testing live up to these expectations in the real world? Would the people support it, or become frustrated with the amount of testing required? And if it is such a good idea, why hasn’t it been tried before?

These are all fair questions, and I will address them in my next piece.