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29 April 2020

Without an army of contact tracers, Matt Hancock’s 100,000 daily virus tests will be useless

The best estimates are that the test will correctly identify at most 70 per cent of cases, and even that is probably generous.

By Phil Whitaker

Charlie was a definite Covid-19 case. He hadn’t had a test: his illness developed ten days before community testing became available in our area. But his pattern of symptoms was identical to countless patients who have consulted me in the past few weeks. The diagnosis was not in doubt.

Being a 58-year-old obese diabetic with high blood pressure he was also at elevated risk, so I sent him to a nearby “hot hub” when he first contacted me, on the fourth day of his illness. The hot hubs were commissioned with impressive rapidity just three weeks ago, in response to modelling that suggested we were going to be overrun during the Easter weekend. I’ve volunteered for several shifts at my local one, located in a self-contained annexe at a neighbouring surgery. It’s been refloored with washable vinyl throughout; personal protective equipment (PPE) is in good supply; and an infection control practitioner cleans every consulting room between patients. At the end of each day, specialist contractors fumigate the entire facility with an anti-viral “fog” that settles on every surface.

Fortunately, despite feeling tight-chested and profoundly fatigued, Charlie’s oxygen saturations proved good at the hub. His blood pressure was, however, shockingly high, necessitating swift adjustment to his medication, which in turn required a blood test a week later to check his kidneys weren’t deteriorating. Blood tests are one of the few things the hot hubs aren’t set up to perform. This was going to be down to me.

To keep our surgery site “cold”, Charlie remained in the quarantine bay in our car park. It must have made a curious sight, a PPE-clad medic crouched beside Charlie’s passenger door drawing blood from his outstretched arm. Afterwards, I checked that his oxygen levels remained fine. This was now day 11, and although he still felt absolutely dreadful, he’d made it past the danger zone for serious deterioration.

Charlie had also heard that community testing for key workers had just been launched at a site about an hour’s drive away. 

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“Can you fix me up with one?” he asked.

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“What do you think it’s going to do?”“Well, if it’s negative, it means I can get back to work.”

I reminded him that simply getting dressed to come to surgery had wiped him out, and suggested that a return to his social care role was still some way off. But his faith in the power of testing was indicative of our current national confusion.

The testing that the Health Secretary Matt Hancock is driving towards – 100,000 per day by the end of April – is for the presence of coronavirus. It seeks to pick up traces of viral RNA on swab samples from the upper airways. The problem is, it performs very poorly. The best estimates are that it will correctly identify at most 70 per cent of cases, and even that is probably generous – hospital colleagues speak of barn-door Covid-19 patients returning multiple negative results, only for viral RNA to be detected on the fourth attempt. 

A negative result is essentially worthless, and certainly shouldn’t be used to send frontline workers back to the fray. If someone has the clinical picture of Covid-19 then they need to be out of circulation whatever their test result. Any value in RNA testing lies purely in when it returns a positive. This should trigger exhaustive identification and quarantine of recent close contacts – the test, trace and isolate (TTI) approach that has thus far controlled infection rates in South Korea, Germany and Singapore.

The UK was doing TTI in its initial “containment” phase, but abandoned the effort once sustained community transmission occurred. Hancock’s 100,000 tests a day will be pointless unless we have the manpower and organisational structures to do the necessary contact tracing for those proven to have Covid-19. Community testing will still miss at least 30 per cent of cases, but the overall effect of TTI in the population at large would be a substantial interruption to the chains of transmission.

Charlie had been driven to surgery by his wife, Diane. After I had taken his blood, Diane said she was sure she’d had the same illness in early February – her symptoms had been identical to those that Charlie had now, and it had taken her seven weeks to fully recover. This would have been weeks before community transmission was first confirmed in the UK, and fits with modelling from Oxford University that suggested the virus may have been in circulation for a month before the first reported death.

Diane may have had something like flu, of course. The only way to tell would be to perform a different sort of test, analysing a blood sample for antibodies against coronavirus, which would confirm that she had previously fought off the disease. So-called serological testing is the holy grail of pandemic management. It is the only way we’re going to get any idea how many actual cases (including asymptomatic, mild, and moderate) have so far occurred – and hence how close we might be to having sufficient population resistance (the infamous “herd immunity”) to protect against a second wave.

Laboratory antibody tests have been deployed in small-scale studies in the Netherlands and the US, and the UK is currently launching its own 1,000-household version. The Dutch study suggested a depressingly low rate of herd immunity; those in the US returned higher results, but their design probably led to overestimation. Cheap, quick, finger-prick kits would be of enormous value. But here, too, low true detection rates are a significant problem.

The only current option to get us out of lockdown is a resumption of TTI. And that will depend on the rapid recruitment and training, from a standing start, of an army of contact tracers. Once again, the UK has been found firmly on the back foot in its response to Covid-19.

This article appears in the 29 Apr 2020 issue of the New Statesman, The second wave