Coronavirus: When to test?

From stewartb:

From a general, non-expert look at what is being written about testing, or the lack of it, mostly based on US sources, I wonder if there may be a complex of different reasons lying behind the decisions that have been taken, and altered over time, in the UK.

Firstly, I suspect there may be a range of different reasons to undertake ‘tests’ – i.e. testing for different disease management purposes. Is it possible that whilst it may be useful to test in order to identify and track an infected individuals’ contacts and then quarantine when numbers are relatively low, this may not be effective/feasible or the prime purpose of testing at a later stage after the more extensive spread of the pandemic? Intuitively, once support for the ‘herd immunity’ strategy was adopted – for whatever reason – and time was allowed to elapse, the feasibility for effective testing for this former, specific purpose may have been reduced or lost. One question for the epidemiologist/statistician is on the extent that testing and tracking contacts now can make good what might have been achieved by testing then.

I can envisage that testing now and subsequently may be directed more at (a) diagnosis of especially vulnerable people who have fallen ill in order to rule in/rule out the virus; (b) ruling out infection so key workers don’t need to be isolated uneccessarily; and (c) testing in a survey of the wider population as part of a statistical ‘surveillance’ exercise. There may be other purposes that I can’t think of.

The following US source discusses the relative failure to test in the USA and identifies a range of reasons, some highly critical of Federal Government bureaucracy:


The following source by contrast focuses on science: specifically it discusses technical limitations in the testing available in the USA.

“The currently available diagnostic test is a PCR test developed by the CDC (US Centre for Disease Control & Prevention), which looks for RNA from the virus. However, hospitalized patients infected with the new coronavirus can have test results that vary from day to day because the amount of virus produced by the body can change throughout the course of the illness, ….”.

It goes on: ‘Repeat testing may be necessary to determine if a suspected person has been infected or when a patient is no longer infectious. “The take home message is that a test that looks at a single time point is not sufficient to rule out infection”.’

And finally: “Evidence from the case in Washington State also suggests that the severity of the illness does not necessarily correlate with levels of the virus in the body – meaning someone can be very infectious without seeming very sick. “That’s why there’s concern that patients who are minimally symptomatic may be fueling the outbreak simply because they don’t feel sick enough to go to the hospital,…”.

Very far from straightforward issues look to be involved. It would be fascinating to have more insights into the decision making processes within the UK governments as they evolved over time on the nature, purposes and perceived value of testing.

4 thoughts on “Coronavirus: When to test?”

  1. The Irish don’t seem to find it so problematic.

    At least in the South -not in the North.

    “Dear @NicholaMallon, you will be aware N Ireland stopped community testing for #coronavirus on 13th March. I want to make you aware that planed tests in North and South Ireland couldn’t be more different. It is clear that BOTH parts of the island need to Test, Test, Test!”

    And in good ol’ USA?

    “There have been deep, systemic, and horrifying failures—most notably our inability to mobilize a testing regime that would provide the data that health-policy leaders need to make every other decision. You cannot understand the cause of a disease, its natural history, or the best ways to prevent infection without the ability to test the population. We have long had that ability—there are hundreds of American universities and medical centers that could create a useful diagnostic for covid-19—but we have never bothered to properly prepare.”


  2. “Indeed, South Korea stands out as an exemplar. After one of the world’s largest initial outbreaks outside China, it has managed to bring daily new cases into relative decline without imposing draconian nationwide lockdown measures. Comparing Italy to South Korea shows how dramatic the differences can be. On March 1, Italy had only 1,701 cases and 41 deaths, while South Korea had 3,736 cases and 21 deaths. Three weeks later, on March 22, Italy’s caseload had exploded to 59,138, with 5,476 deaths, while South Korea’s total caseload had merely doubled to 8,897, with 104 deaths.

    The key to South Korea’s success has been speed and an early push toward mass testing, rigorous contact tracing, and mandatory quarantine for anyone near a carrier of the virus.The key to South Korea’s success has been speed and an early push toward mass testing, rigorous contact tracing, and mandatory quarantine for anyone near a carrier of the virus. The country, with a population of 51 million, tests more than 20,000 people a day at more than 600 testing sites nationwide, while integrating apps that not only track individuals if they have tested positive, but also warn them if they might have been exposed to a known case.
    Yet in the United States and the United Kingdom, there is a public and internal government debate over whether testing matters—particularly for those who are only having minor symptoms. As of March 20, South Korea’s rate of testing was 6,148 per million people, while the United Kingdom was testing only 960 people per million and the United States just 314. Why waste resources and time trying to identify who has the disease, these officials ask.

    In fact, the U.K. government even took a strategic decision on March 12 to stop testing those who have mild symptoms, those coming into hospitals but not admitted, or even the country’s health workforce. This was a dangerous and shortsighted decision, as Prime Minister Boris Johnson’s U-turn less than a week later, when he committed to a goal of 25,000 tests per day, reveals.”


  3. Not just South Korea. China, too. This extract is from an interview with Bruce Aylward of WHO. The reason for testing for covid 19 is not complex but simple public health means of preventing disease.

    Bruce Aylward
    “I think the key learning from China is speed — it’s all about the speed. The faster you can find the cases, isolate the cases, and track their close contacts, the more successful you’re going to be. Another big takeaway is that even when you have substantial transmission with a lot of clusters — because people are looking at the situation in some countries now and going, “Oh, gosh, what can be done?” — what China demonstrates is if you settle down, roll up your sleeves, and begin that systematic work of case finding and contact tracing, you definitely can change the shape of the outbreak, take the heat out of it, and prevent a lot of people from getting sick and a lot of the most vulnerable from dying.”

    Liked by 1 person

  4. Gaungdong province in China really showed what can be acheived when there is no dithering. It has the largest population in China 113 million and was less than a week behind Wuhan. They jumped to it, testing, testing, testing along with tracking contacts and quarantining. I believe in Gaungzhu, the capital city of Gaungdong, were using electronic wristbands, to check on the movements of those quarantine. Result; 1483 infected cases and 8 deaths.

    I try not to compare the above with the UK response, for fear of my spleen bursting.


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