Samar Razaq is a GP in Burnham and is on Twitter @samarrazaq.
“The man who promises everything is sure to fulfil nothing.” Carl Gustav Jung.
The Prime Minister recently announced one of the most ambitious testing plans to help overcome the gridlock the country is facing due to rising cases of coronavirus. Termed “Operation Moonshot”, Boris Johnson announced plans to carry out up to 10 million tests in a day to allow people who are negative to be able to continue with their life as normal. This will allow the entire UK population to be tested every week, no mean feat indeed. The announcement came on the backdrop of news of inadequate laboratory capacity to fulfil current needs for testing. Also, due to localised outbreaks, testing capacity has been shifted to certain parts of the UK where prevalence is the highest, leaving others from low prevalence areas a possible journey of hundreds of miles to testing sites if they are symptomatic.
How will it be possible to scale up testing to such a level whilst we continue to struggle to fulfil demand of a few hundred thousand tests a day? The hope is being placed in technological advancements where rapid tests can be carried out on saliva which give results in 20 to 90 minutes. Other tests that have been part of government trials since the summer may be able to provide results in seconds as they work much like a pregnancy test. If successful, this would be the largest screening exercise this country will have ever seen. But, is it feasible, or even desirable?
Carrying out tens of millions of tests a day would require distribution of tests out to individual households and people to carry out tests on themselves. No matter how quick its turnaround time, any test that requires laboratory machinery to give a result will face the same challenges of capacity and logistical delivery that we face now. This new plan, therefore, can only be realistically carried out with pregnancy style tests which give results within seconds or minutes. However, how would the integrity of such a system work? If an airline requires to see the test results before one embarks on a plane, how many people would be tempted to fake their result in order to avoid cancellation of the dream family holiday, or to see a loved one over Christmas?
This would mean the large majority of those testing positive and their families being needlessly isolated
There is, however, another stumbling block bigger than the logistical nightmare of millions of daily tests. Quick tests generally struggle to have both high sensitivity and specificity. However, let’s be generous and assume that there are rapid tests in the pipeline which have a sensitivity and specificity of 99%, figures which would be amazing to achieve. According to the Office of National Statistics, the prevalence of Covid-19 for the last few months has just been hovering under 0.1%, at reasonably stable levels. If we test 10 million people a day with the disease at current prevalence levels, with a test that is 99% sensitive and 99% specific, we would achieve a positive predictive value of just 9%. That means anyone testing positive would have a 9% chance of actually being a true positive. This would mean the large majority of those testing positive and their families and contacts being needlessly isolated, contrary to good screening practice. A test at such low prevalence levels would have to be pretty much 100% specific to give meaningful results. But high specificity is usually achieved at the expense of sensitivity, a reduction in which would in turn reduce the negative predictive value.
According to the BMJ this uncertainty is planned to be financed to the tune of a £100 billion, almost the entire yearly budget of the NHS. The plan is to have the system up and running by the spring with most of the money likely to end up with private contractors and companies. Is this the UK taking the world lead in technological advancements in testing or just a smoke screen to cover up for the chronic under funding of the NHS, as Covid-19 and the usual winter ailments line up to simultaneously assault general practice and the hospitals?
This uncertainty is planned to be financed to the tune of a £100 billion
There are encouraging signs that the virulence of SARS-CoV-2 may be reducing. Despite daily cases being around the thousand mark for the last few weeks, the death rate has been thankfully low. One of the theories has been that the virus may have become less virulent, a trait not unusual to viruses as they require their host to survive to propagate themselves. Another reason could be better management techniques as the modus operandi of the virus has become clearer. Perhaps the government knows this and is hoping that by the spring such an ambitious testing programme will not be needed. The promise won’t have been broken if, by then, victory over the virus can be claimed. For now, it seems, we are planning to fly to the moon when all we have is a paper plane.
