April 28, 2021

expert reaction to BMJ opinion piece on mass testing

An opinion piece on mass screening for asymptomatic SARS-CoV-2 infection from Mike Gill and Angela Raffle has been published in the BMJ.

Dr Michael Joseph Mina, Assistant Professor of Epidemiology at Harvard T.H. Chan School of Public Health, said:

“I do not agree with this sentiment. Testing is our eyes on this virus. Without testing, we simply cannot see it. The more eyes the better – particularly when there is little downside.

“If the testing is as easy as brushing your teeth, then it’s a great addition to a comprehensive plan to limit spread. And it can be dynamic. The testing can be throttled up or down depending on the transmission of the virus within the population at the time. When cases are at a minimum, we can slow the testing down. But as long as people are already accustomed to it and have access, then if cases start to rise in a given community, then the testing can be throttled up enough to limit spread.

“Importantly, this type of testing doesn’t need to be perfect. To stop outbreaks from growing and rapidly reduce outbreaks that exist already, we don’t need 10 people to go on and infect 0 people, we only need to get 10 infected people to go on and infect 9 additional people. If we could do that, then after a month 100 infected people would become 40 new infections per day. On the other hand, if 10 people go on to infect about 13 additional people (which is the rate (R = 1.3) that has happened during this pandemic) then after a month those 100 infections would become 600.

Mistaking the need for success versus perfection in a pandemic is a mistake. We don’t need perfection in public health, we just need success. And success here is an imperfect blockade of transmission that keeps, on average, 100 infected people from infecting more than 100 additional people. That’s all we need to entirely abrogate large outbreaks.

“Testing during this pandemic has largely been driven by a paternalistic and highly conservative attitude with an underlying theme that the public is not capable of making informed decisions based on their results. Making testing accessible to anyone who cares to know their status is crucial to control of the virus. 

“If we focus only on symptom-based testing, especially with laboratory tests that are not rapid, we tend to miss a majority of the transmission window for people. 

“People reach their peak virus load very quickly – within 24-48 hours of first becoming detectable on even the most sensitive tests. This swift upswing in virus load occurs before most people become symptomatic, which is often immunologically driven, and points towards the importance of detecting infections before they become symptomatic – or pre-symptomatic. The authors state that capturing asymptomatic individuals through routine testing is not important because ‘Evidence is growing that transmission arises overwhelmingly from people with symptomatic infections and their contacts’.  This misses the most important aspect of frequent accessible rapid testing – which is intended to catch people quickly and, most crucially, potentially pre-symptomatically.

“The authors’ statement is at best incomplete. The authors cited papers that are not up to date, but rather using two papers from the earliest months of this pandemic. It is ironic that they state ‘Evidence is growing’ when they pick two studies that explicitly didn’t consider pre-symptomatic testing.

“They additionally seem to conflate screening for medical purposes from screening for a highly transmissible respiratory virus. The comparison of screening for this virus – which is a public health purpose – with screening for two medical issues: cervical cancer and phenylketonuria – demonstrates a clear confusion by the authors of why accessible testing is necessary in this particular pandemic. This is not medical testing. This is testing to mitigate transmission. The purposes are simply different. Providing people with the tools to know if they are infectious is not a danger to society. Concerns over false positives are overstated and miss the most important attribute of rapid tests – that they are rapid and can be repeated immediately if positive and this can get the false positive rate to less than 1 in 1000 and our results show it is even better than this. The authors also point toward a concern that testing will provide people with a false sense of security. The point is – these tests work very well when people are most transmissible.

“This argument is old and tired. It is an argument that was made with home pregnancy tests, with non-prescription HIV tests and was even made about seatbelts – that people would drive recklessly because they had a seatbelt on. In all of these cases, the benefits outweigh the risks. The benefits of a testing program that is very accurate when people are infectious outweighs the slight risks that some might have a false sense of security when negative. At the end of the day, offering people ready access to testing, on their own terms is how we fight a pandemic – along with vaccines and other measures.

“We have to put the public back into public health. Giving them tools to be able to know they are infectious is one of the best things we can do to slow transmission.”

Prof Mark Woolhouse, Professor of Infectious Disease Epidemiology, University of Edinburgh, said:

“In their editorial for the British Medical Journal Raffle and Gill argue that targeting asymptomatic infection by mass testing is not an effective means of controlling novel coronavirus. This misses a large part of the rationale for asymptomatic testing.

“The control of an infectious disease such as COVID-19 depends crucially on finding cases, and finding them early, ideally before the infection can be passed on.

“People infected with novel coronavirus are infectious for 24-48 hours before they show symptoms, and this period is thought to account for up to half of all transmission.

“This pre-symptomatic infectious period makes novel coronavirus much more difficult to control. Asymptomatic testing can reveal these crucial pre-symptomatic infections – there is no other way to do this.

“Before undertaking an activity that might put others are risk – going to work or school, visiting relatives or attending an event – many people would like to know their infection status. Testing does that. It reduces the risk and, if people act on their test result, it reduces transmission.

“There are numerous challenges in making a large-scale mass testing programme work effectively, but the better it works the less need for social distancing measures, now or in the future.”

Prof Paul Hunter, Professor in Medicine, The Norwich School of Medicine, University of East Anglia, said:

“Totally agree with the paper on asymptomatic testing. It’s hugely expensive and will not achieve much, as has been repeatedly pointed out. The main issue that we are seeing now is as case numbers are declining across the country COVID seems to be retreating to areas where is remained a problem last summer (i.e. the UKs more deprived areas). We know from the Liverpool trial and elsewhere that it was these more deprived areas where transmission was highest and where uptake of testing was poor and also uptake of vaccine is poorest.  So how twice weekly testing predominantly by middle class families in areas of low transmission will do anything to affect transmission in our more deprived locations is not clear to me. We would do better by trying to support people in these higher risk areas to self-isolate.”

‘Mass screening for asymptomatic SARS-CoV-2 infection’ by Angela Raffle and Mike Gill was published in The BMJ at 23.30 UK TIME on Wednesday 28 April 2021.

DOI: 10.1136/bmj.n1058

Declared interests

None received.