Confirmed cases by test types

What proportion of cases in England fall into each test category?

Anthony B. Masters

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Counts of confirmed cases depend on the viral testing regime, capacity, and willingness. In England, there are three main ways to get a positive test:

  • PCR only: A person, often with symptoms or regular testing, takes a polymerase chain reaction test.
  • LFD (positive PCR): After taking a rapid test, it shows a positive result. That person then undertakes a confirmatory PCR test, which is also positive. The swab for the latter test is within 72 hours. If all such tests are negative, then analysts remove that case.
  • LFD only: The person gets a positive result on a rapid test. In some circumstances, there is no PCR test within the three-day window. As such, the reported positive result remains.

There are also loop-mediated isothermal amplication (LAMP) tests. This kind of test does not have its own category.

For each person in England, only their first confirmed positive result counts as a new case. At present, reinfections do not add to reported case counts.

In November 2021, there were around 798,000 new cases with only PCR tests. About 177,000 positive rapid devices were later confirmed by PCR tests. Also, around 30,000 cases came through a rapid test without a lab test.

One in five (21%) new cases in England involved a rapid test.

The statistics are from reported cases up to 29th December 2021. These figures are subject to change, with new cases report.

(Image: R Pubs)

Comparability of cases

The United Kingdom has four public health agencies, which make different decisions. That reduces comparability between their published statistics.

The major differences are:

  • Only confirmed cases in England can involve a rapid test. The other three nations do not use results from these devices in confirmed counts.
  • Public Health Wales uses a six-week ‘episode’ period. That means many positive results within six weeks only count once. One person can have several cases — as long those positive tests are more than 42 days apart. Agencies in England and…

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Anthony B. Masters

This blog looks at the use of statistics in Britain and beyond. It is written by RSS Statistical Ambassador and Chartered Statistician @anthonybmasters.