Testing Pillars

Local confirmed cases now include commercial testing.

Anthony B. Masters

--

On 2nd July, Public Health England updated their COVID-19 reporting. This update meant we can see confirmed cases in both main testing pillars.

This article examines the Leicester lock-down, and confirmed cases in Wiltshire.

Pillars

There are two types of test for SARS-CoV-2: whether you currently have the virus and whether you have had it. Antigen testing is for whether you have the virus.

The UK government has two main ‘pillars’ for its antigen testing programme:

  • Pillar 1: NHS and Public Health England laboratories;
  • Pillar 2: testing by commercial partners.

A confirmed case means a laboratory test gave someone a positive result for SARS-CoV-2.

Before 2nd July, the PHE daily dashboard showed ‘total cases’ for local authorities. There was a major limitation, which was only reflected in the notes:

The UK total is not the sum of the 4 National totals as the pillar 2 cases cannot currently be included in the individual National totals for England, Northern Ireland and Scotland. All other data on this website are based only on cases detected through pillar 1.

As the Financial Times highlight, including ‘pillar 2’ confirmed cases transforms our view. There was an increase in confirmed cases in Leicester.

‘Pillar 2’ confirmed cases rose, as cases confirmed by the NHS and PHE labs declined. (Image: PHE)

Looking at ‘pillar 1’ confirmed cases gives the wrong impression. This outbreak is visible among the ‘pillar 2’ confirmed cases. The relative scale of the Leicester outbreak may be an artefact of increased testing.

When did Public Health England know?

We can look at the Public Health England surveillance report for week 22. The graph shows ‘pillar 1’ confirmed cases by English local authority:

The populations are the 2018 ONS mid-year estimates. (Image: PHE)

By week 23 (4th June), the updated graph shows confirmed cases for both testing pillars:

--

--

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.