The majority of COVID-19 testing in the UK to date has been Polymerase
chain reaction (PCR) testing which is lab-based and tests for the
presence of SARS-CoV-2 virus (rather than testing for the body's
immune response or antibodies). This data shows the number of people
who received at least one PCR test in the previous 7 days, as well as
the percentage of people who received a PCR test in the previous 7
days who had at least one positive PCR test result (the positivity
rate). People are only counted once in a 7 day period.
Lateral flow device (LFD) virus tests are another type of COVID-19
test that look for the presence of SARS-CoV-2 virus. These are also
swab tests, like the PCR tests, although they give results in less
than an hour, without the need for laboratory processing. LFD tests
are generally used for mass and routine testing of people who do not
have COVID-19 symptoms. They are aimed at identifying individuals who
may be infectious asymptomatic carriers and potential transmitters of
the virus so these people can isolate and take the virus out of
circulation in the community.
PCR Positivity rate (weekly percentage of individuals tested who
test positive for COVID-19)
It is important to consider test positivity with caution and
alongside the other measures such as confirmed case numbers and the
information available on those being tested.
A higher percentage of positive tests could suggest higher
transmission, and perhaps that there are more people with coronavirus
in the community who have not been tested yet, which could further
indicate a need for conducting a higher number of tests. However, it
could also be that a change in positivity is related to different
groups of people coming forward for testing. It is likely a mixture of
How testing has changed over time
The overall number of virus tests conducted (using lab-based and rapid
tests) each day is only available at a national level.
For local areas (West Sussex or its districts and boroughs) we can
only see the number of individuals tested using PCR tests in a seven
day period or the total number of LFD tests conducted each day. These
two measures cannot be combined into a single metric for how many
people are being tested and must be considered separately.
The next figure shows how the rolling 7-day number of individuals
tested has changed over the course of the pandemic, and particularly
how testing ramped up towards the end of 2020.
The next figure shows the proportion of individuals with a positive
result for the same area as in the above barchart. Comparing these two
charts helps to contextualise testing. It shows that whilst the number
of tests in the early stages of the pandemic were low, a much higher
proportion of tests were positive (in some cases around half of
tests). In more recent months, many more tests are conducted but fewer
of those are positive.
Individuals are counted once in any 7 day period even if they have
several PCR tests.
Whilst the number of individuals tested using the lab-based PCR tests
is available for the whole of the pandemic (since February 2020), LFD
testing in England only became widely available from the 21st October
the time period for the next figure (number of LFD tests conducted)
is much smaller (for the last few months only).
Note also that data are available for very recent days (up to the day
before). Whilst test results are much quicker to obtain for LFD tests
compared to PCR tests, it is expected that the totals for the last few
days will still not be complete due to delays in getting results into
the national data systems.