In praise of lateral flow

Taking a look at the (somewhat incoherent) reference 2 in the Financial Times, I was directed to the year old paper at reference 1, about the trade-offs between Covid tests which were cheap and quick and tests which might be more accurate but which were slow and expensive. One of the trade-offs being that slow and expensive produced too many results which were positive but not of concern, the purple zone in the figure above, lifted from reference 1. False positives of a sort. 

While the figure above is the adapted version printed by the FT in reference 2. FT quite reasonably points out that there is a one to two day window of failure at the start of an infectious episode, during which infection will not be detected by LF tests. A window which will be difficult to close given the rapid growth of the viral load in this period.

And while it was reasonable for the FT to point to the weaknesses of the LF regime, I thought its subtitle was unhelpful. My reading of reference 1 was that lots of LF testing - and following through the results with behaviour - would be helpful in pulling down rates of transmission and in pulling down the need for isolation. At a population level it is a good deal better than doing nothing.

But getting the right regime, given the numbers and costs involved, looks to be a complicated business, so lets hope our ruling classes have deployed the right people for getting it right.

I did not notice anything about the sort of errors noticed at reference 4, although one supposes that they are being looked at too.

PS: in the margins of all this I came across a nearly-new-to-me word in the Maigret story at reference 3; nearly new in the sense that I have read this story before but cannot now remember having looked the word up before. The word being 'chaudrée' and the context suggesting a first course of a three course meal. Not present in either Larousse or Littré, but on rising Bing reveals all: a stew, usually a fish stew, what our New England friends would call a chowder. Ultimate root 'chaud' from the Latin for heat, by way of 'chaudron' for a small cauldron, suitable for domestic cooking. Also, I believe, something used for humping coals about the apartment buildings of old Paris. Most of these stews seem to be white and I am not sure that I approve of red, as snapped above, which I suspect of being too hot for my palette. And I certainly do not approve of lemon garnish; far too sharp for eating. Sucking on the school football field, possibly. From the Canadian website at reference 5. A website which I have yet to categorise, involving, as it does, advertisements, shopping, magazines and recipes. I dare small ads too but I have yet to find them.

References

Reference 1a: Rethinking Covid-19 test sensitivity - a strategy for containment - Michael J. Mina, Roy Parker, Daniel B. Larremore - 2020.

Reference 1b: https://www.nejm.org/doi/pdf/10.1056/NEJMp2025631.

Reference 2: Omicron puts spotlight on UK’s use of rapid tests to stem Covid spread: Lateral flow devices are a key part of the government’s strategy against coronavirus but their efficacy is questionable - Hannah Kuchler, Oliver Barnes, Financial Times - 2021.

Reference 3: Le Voleur du Maigret - Simenon - 1967.

Reference 4: https://psmv5.blogspot.com/2021/11/the-p-value-battle-continues.html.

Reference 5: https://www.circulaire-en-ligne.ca/.