The Covid testing dilemma

England’s pushing mass testing as a way to contain Covid. It’s free, it’s government approved, it’s somewhere between uncomfortable and painful, and it may or may not be a good idea. Let’s tear the numbers apart and see what we can figure out.

Since the schools reopened, secondary students–those are the older kids–have had to do quick Covid tests twice a week, and that’s been a bulwark of the program to keep the schools open while not letting the virus get out of control. 

The tests, unfortunately, have a reputation for being unreliable, especially when done by non-experts. Since the kids are doing their own tests, or asking their parents or three-year-old sisters to stick the swabs up their noses and down their throats, these are in the hands of the distilled essence of non-expert. One fear about relying on the quick tests has been that false positives will send a lot of people into isolation unnecessarily. So half of the positive tests were sent to a lab to be confirmed by the slower, more reliable tests, and only 18% of them were false positives. 

Irrelevant photo: Rhododendrons. Photo by Ida Swearingen

But wait, because we’re not done yet. Those numbers are from March, and Covid rates have fallen, at least in parts of the country. (Some hot spots remain, and I don’t know if numbers are falling there as well. Just put that possibility off to one side. The recipe may call for it later. If it doesn’t, we’ll stick it in the freezer.) The point is that where the number of cases is lower, everything changes

Why? Because the tests will crank out the same number of false positives, no matter how many people are infected. Find yourself a population of people who’ve never been exposed to Covid and the test will swear on any religious book you like that some of them are infected. 

I’m about to throw some numbers at you, so if your allergies are bad today just skip a few paragraphs.

Ready? In London, the southwest, the northeast, and the southeast of England, the prevalence of Covid ranged from 0. 08 to 0.02. In England as a whole, it was 0.12%. Using those figures (I’d assume that means the England-wide ones), it would take 16,000 tests to find one infected person. If the tests cost £10 each, that means spending £160,000 to find that one person.

Is that worth it? If we were trying to stamp the disease out and keep it stamped, as New Zealand is, it would be. Given that we treat stamping it out as the silly thought of irresponsible day dreamers, probably not. 

Meanwhile, in leaked emails (I do l love a good leak) “senior government officials” are talking about scaling back mass testing, although the Department of Health and Social Care says it has no plans to end the program. One in three infected people, they remind us, show no symptoms but is still contagious. 

That brings us neatly to the question of whether the rapid tests will spot that one person. In other words, it’s time to talk about false negatives. Administered by an expert, the tests pick up 79% of infections. Or to put that the other way around, they miss 21%, and those are mostly people with a low viral load. Or to put that another way, they’re most likely to miss people who don’t have symptoms, who are just the people the testing program is looking for.

Administered by secondary school students or their three-year-old sisters, they’re more likely to pick up 58% of infections, or to miss–umm– I think that’s 42%. Although estimates of the number of cases the test misses vary. It might be as high as 50%. 

The government denies that it has any plans to scale back anything ever and Boris Johnson is urging everyone to get tested twice a week. Even though his advisors say that in areas with low infection rates, only 2% to 10% of the positive results may be accurate. 

But what the hell, guys, we’ve got these tests. Someone’s cousin has the contract for them. Use them, will you, please? For the good of the nation.


News of an accurate rapid test that’s in development

A new test is being developed that’s both fast and accurate. It also tracks variants and tests for other viruses that might be mistaken for Covid. It can screen 96 samples at a time and within 15 minutes it starts to report the samples as negative or positive. In 3 hours, it will have sequenced all its samples. 

It’s also small and portable. It doesn’t make coffee, but it just might be able to make you a cup of tea.

Juan Carlos Izpisua Belmonte, a professor in Salk’s Gene Expression Laboratory where it’s being developed, said, “We can accomplish with one portable test the same thing that others are using two or three different tests, with different machines, to do.”

That’s the good news. But will it go from development to being manufactured and used?

Market analysis would be required to determine whether the initial cost of commercialization—and the constant tweaks to the test needed to make sure it detected new variants or new viruses of interest—are worth it.”

I believe that translates to “maybe.”

It’s called NIRVANA, which doesn’t seem to stand for anything, so I don’t know why it’s in all caps. 


High- and low-tech approaches to Covid

In New Zealand, they’re trying out an app that connects to smart watches and fitness trackers, monitoring people’s heart rate and temperature. It’s called an Elarm and the developer claims it can spot 90% of Covid cases up to three days before symptoms appear.

Does that include people who don’t go on to develop symptoms? I’m have to give you a definite maybe on that, because the article I found doesn’t address it. The company’s own website doesn’t answer the question either but says it will also let you know about stress and anxiety, although you might notice those without needing an app. Basically, it figures out your normal levels and lets you know when you’ve wandered off them, so you could end up going into isolation over the flu as easily as over Covid. That would scare the pants off you but would, at least, take a lot of the punch out of flu season.

So how do you use this? New Zealand wants its border force to try it out, since almost the only cases of Covid there are in incoming travelers, who have to go into quarantine, meaning the people who work for the border force are in the front lines.

When New Zealand says quarantine, by the way, they actually mean quarantine. It’s one reason they’ve been able to contain the virus.


On the other end of the scale comes the recommendation that we open windows in public places to minimize Covid transmission. It’s cheap, it’s simple, and–

Oh, hell, how many public places these days have windows that open? Okay, ventilation. The air in public indoor spaces needs to be replaced or cleaned. 

We’ve heard a lot about keeping two meters (or yards) away from people to avoid contagion, but in addition to the heavier droplets people breathe out, which can carry Covid, the tiniest particles that we breathe out can also carry it, and they can stay suspended in the air for hours. The goal is to run them outside and get some fresh air in. 


If you’re looking for a low-tech way to decide how far from people you should be standing, you can think of it this way: If you can smell that they’ve had garlic or peanut butter for lunch, you’re too close. 


Drug news

An asthma drug, budesonide, has been shown to shorten people’s Covid recovery time –and it can be used at home without anyone involved needing welding gloves, a deep-sea diver’s helmet, or a set of allen wrenches. It’s relatively inexpensive and comes in an inhaler. It shortened people’s recovery time by three days and at the end of two weeks the people who used it were in better shape than the control group.

It’s not clear yet whether it made hospitalization less likely. In the budesonide group, 8.5% were hospitalized. In the control group, that was 10.3%. That sounds like a result, but the problem with interpreting the numbers is that hospitalization rates are dropping in Britain. If you want to understand why that makes the numbers hard to interpret, you need to talk to someone who actually knows something.

Everyone in the test was over 50 and had underlying health problems. The drug can be used in the early stages of infection. 

17 thoughts on “The Covid testing dilemma

  1. For people with even moderate anxiety issues, an app that keeps bleeping to tell you that your temperature is a tiny bit higher than normal would be a nightmare. I know very well when my anxiety levels are high, and something that kept bleeping to tell me that my temperature was up a bit, which could just have been because I was walking in warm weather and had stupidly put a winter coat on, or had put my FitBit on straight after having a hot bath, would make them a lot worse!! Who thought that one up?

    Liked by 4 people

    • Good question. I’d like to think it’s a little better planned than that–that it’s not quite that blunt an instrument–but I make no promises. It could just be one more bit of oversold tech. And I hadn’t thought about the insanity of something beeping to tell you, “You’re anxious. You’re still anxious. Do you feel anxious??” How helpful. I want one. No, I want three, one for each wrist.

      Liked by 2 people

    • The “rhythm method” of birth control works (to the extent that it does) because many young women’s temperature rises slightly during the optimum time window for conception. They’re going to spend that time being beeped at? Having their hormone cycles advertised? At the office? ???

      Liked by 2 people

      • I wouldn’t swear to this, but I’d assume the app’s smart enough to know that. Presumably. It does work out a baseline of what to expect from an individual. But since much of the medicine we rely on was tested on men because taking women’s cycles into account seemed too complicated–well, who knows?


  2. Who wouldn’t want to help out a cousin or friend in times of hardship. It shows the greatest of kindnesses when you can harness the full coffers of the public purse for this aid.
    Honestly, when people accuse non-Western countries of corruption, and so much is going on our own backyard, it makes me roll my eyes at their blindness.
    Sorry, am venting in a place completely different to the original source of grievance, so that helps nobody but me. So, errr, thank you!

    Liked by 2 people

    • You make a good point, though. I sometimes think that people get more exercised about the low-level corruption than about corruption at the top. Because we understand it. Because we experience it directly. The big guys, though, have a thousand ways to obscure it.

      Liked by 1 person

  3. I think that making kids stick the swabs up their noses is by far the most stupid decision Germany made. I just don’t approve of that. Supposedly it’s mandatory, then a friend refused to send her children to school for this reason. Dunno what happened next. Knowing her, she’s most likely sticking to her decision. I’d have probably done the same.

    Liked by 1 person

  4. The talk of testing over here has sort of been muted by the surge of vaccinations I guess. (Or pushed off the news by all the shootings – mass and otherwise.) At my recent routine doctor appt getting a test wasn’t even a subject.

    “withoutwimbledon” made a great point about the anxiety app. It’s been a pleasant (relatively speaking) surprise how much attention has been paid to the effect the isolation and general pandemic fears have had on people’s mental health. Usually that is pretty back burner stuff.

    At least the nepotism continues apace. We all have relatives who need that extra boost of support !

    Liked by 2 people

  5. Pingback: The Covid testing dilemma – sport

  6. Ellen I’ve been meaning to thank you for your very insightful posts on the pandemic. My husband is studying it in depth to keep up with solid information, since we are both high risk. I’ve sent him the links to several of your posts.

    Liked by 2 people

    • Thanks, Leah. I’m glad I’ve been useful in the midst of this. And I’m glad he’s studying it seriously. I wish more people would–although I know not everyone has the time or interest. If he doesn’t already subscribe to the Science X and Medical Express newsletters, they’re where I draw a lot of my links from. I find them both useful and (usually) accessible to a non-scientist.

      Liked by 1 person

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