Community testing for COVID-19: reaching 25 million tests per week

Until recently, the strategy for COVID testing in many countries has been focused on people who have a significantly likelihood of having COVID-19. The need to impose unpleasant social distancing measures, and ultimately complete lock-downs, trades off against how much testing you do in the community. With sufficient community testing, you could suppress COVID in a population without any social distancing measures. This post is an outline of one way one might go about testing 25 million people per week in order to achieve this.

Decentralised testing

Reaching this sort of scale quickly is likely to require a decentralised approach levering existing organisations. The most obvious candidates to do this are schools and larger businesses. Thirteen million people are employed by businesses with more than 50 employees, and there are twelve million children in schools. If these businesses and schools could test everyone within them each week, 25 million tests would be carried out.

It’s important to note that this sort of testing is completely different from the testing of symptomatic, or likely infected, individuals. Symptomatic testing rightly requires specialist training, uncomfortable nasopharyngeal swabs, and full PPE for the person testing and the person being tested. This is because there is a high risk of exposure to COVID-19, and because getting a test result wrong could have major implications for care.

Testing random individuals from a population with low incidence of COVID-19 poses no greater risk than interacting with them in any other way, as colleagues or students. And in this setting a significant rate of false-negatives or false-positives can be tolerated without major consequences.

Testing procedure

In this proposal all of these businesses and schools would be supplied with: simple nasal swabs, frozen plates containing COVID-19 RT-PCR mix, a basic one-button thermocycler, a blue light transilluminator.

The employee responsible for testing takes one of the frozen plates out of the freezer and thaws it.

Students and employees go up, one by one, to the testing station. Each person takes a nasal swab and swabs their nostril (front-of-nose, not nasopharyx), then places the swab into a well of the plate, and cuts off the swab’s shaft and discards it. They also write their name on a sheet in a box representing this well, then wash their hands.

Once the plate is full of samples the employee responsible for testing takes the plate. They seal it, load it into the one-button-thermocycler, and press the button. The thermocycler runs an RT-PCR programme for an hour.

The employee takes the plate out of the machine and examines it with the blue light transilluminator. Any positive wells (including a pre-loaded control well) will glow brightly. Negative wells will be dull.

If the employee notices any positive wells (a very rare occurence) they immediately look at the sheet of names and contact the person in question to ask them to report to public health authorities for confirmatory testing. If this test comes back positive then contact-tracing begins.

The aim would be to test each person at these schools and businesses once each week.

Costs and availability

The reagents for this test cost much less that £1 per tested person.

A thermocycler is a simple device which can be currently be purchased for £3,200, and likely manufactured for much less. Unlike ventilators, these could be relatively easily produced by other manufacturers. There would be a definite need to scale up production to achieve this scale.

A blue light transilluminator can be made for less than £40 from commonly available materials.

It seems likely that, despite their low-cost, global supplies of RT-PCR enzymes are insufficient for this scale of testing at present. But there is no reason I am aware of to think that this could not easily be scaled up. The quantities of primers needed are readily available.

There might be a need to scale up the production of the DNA-binding dye.

All of these costs are minuscule compared to the economic losses averted by preventing a lock-down.

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