Effectiveness of COVID-19 testing and antibody testing in Scotland: FOI release

Information requested

You asked for:

"I would like if you could confirm please what constitutes covid 'cases' the cases you report to the public every day/week?"

Then you stated - "obviously your number of cases that you report are from the pcr test ie the number of positive pcr test results. Its just I notice on public health England's information on the pcr test, it clearly states that the pcr test will find a small trace of a virus but it CANNOT TELL IF THAT TRACE IS INFECTIOUS

If that is the case then what covid figures are you reporting to the public?"

Response

While our aim is to provide information whenever possible, under section 17 of FOISA and in this instance the Scottish Government does not have the information you have requested.
However, you may wish to contact Public Health Scotland, who may be able to help you. Please see the following links – 

Freedom of Information (FOI) and Environmental Information Regulation (EIR) requests - Contact us - Public Health Scotland

General enquiries - Contact us - Public Health Scotland

You may wish to note the following –

There are two types of test for COVID-19 currently in use in Scotland: viral (PCR) testing and antibodytesting. PCR tests are used to detect if someone is currently infected with the virus; and antibody testing is used to tell us if someone has had the virus.

PCR tests, used to test for current infection, operate as a swab taken from the nose and back of the mouth, with the sample collected sent to one of the existing NHS Scotland laboratories, or the Glasgow Lighthouse Laboratory, to be analysed. Any positive cases identified are automatically followed up for contact tracing through our national system of Test and Protect.

Antibody testing is used to test for past infection. In Scotland currently, it is used to track what proportion of the population has already been exposed to the virus. We don’t yet know whether people who have had the infection are immune and cannot get infected again, nor how long any immunity, if proven, may last. Until this evidence base develops, our current policy is to use antibody testing for population surveillance purposes, and in limited clinical scenarios. In addition to PCR testing, and antibody testing, Scotland has world leading research expertise in viral genomics. Genome sequencing of the COVID-19 virus is currently being undertaken by a Glasgow and Edinburgh partnership working as part of the COVID-19 Genomics UK (COG-UK) Consortium. Whole Genome Sequencing contributes to our understanding of how the disease moves through the population and changes over time. In particular it can improve our understanding about whether cases are likely to be linked or not. As rapid sequencing is now being delivered in Scotland (with results available within 48 hours of a sample arriving at the appropriate laboratory) it has the potential to play an important role in providing information to support the management of outbreaks. Whole genome sequencing can also show geographic links – and help us understand what region or country that virus emerged from.

No test is perfect, and understanding the limitations of the tests we currently use is important. If we assume tests are perfect, and that results always accurate, we put others at risk. In PCR testing, the key risks are false negative results – where a test is negative but the person tested does actually have COVID-19 and is infectious – and occasions where the test is positive but the person tested is not infectious.

False negative results can happen if a swab misses collecting cells infected with the virus, or if virus levels are low – for example, at the start of an infection. The risk to others of false negative results is clear – an infectious person who receives a negative result risks transmitting the virus to others, including vulnerable people who can suffer very severe harm. In certain situations, testing again after a number of 5 days – when levels of the virus may be higher and therefore detectable – can reduce the risk of false negative results having serious consequences. Weak positive results can happen when the swab picks up fragments of the virus from an individual who is no longer infectious.

Laboratories in Scotland have now implemented confirmation testing (or repeat testing) in certain circumstances to confirm whether weak positive test results are actually infectious cases. We will also actively monitor developments around testing innovation so we can take advantage of any new opportunities from testing they present.

About FOI

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