FOI/2021/2868
You asked
Please supply the following information:
1) What diseases do you use a PCR in isolation, to diagnose a medical case of the disease?
2) Has the definition of a 'medical case' changed since December 2019. If so what was it before and what is it now.
3) Why isn't a PCR test used to diagnose AIDS or cancer?
4) How accurate does your data suggest the PCR test to be?
5) Does the covid PCR test identify if a person is actually sick? Or has a viral load that could be transmissible?
We said
Thank you for your request.
The COVID-19 Infection Survey is a household survey that estimates the number of people testing positive for infection and for antibodies in the UK. Our statistics refer to individuals in the community, by which we mean private households. These figures exclude infections reported in hospitals, care homes or other institutional settings.
In the COVID-19 Infection Survey, real-time reverse transcriptase polymerase chain reaction tests (RT-PCR) are used to test for the presence of SARS-CoV-02, the virus that causes coronavirus (COVID-19). Your query about other diseases may be better placed with Public Health England (PHE). They can be contacted via email at wn_coronavirus@phe.gov.uk.
Unfortunately, we do not hold information on whether the definition of 'medical case' has changed or why PCR tests are not used to diagnose AIDS or cancer. Please see the above contact details for PHE, who may be better placed to assist.
Test sensitivity measures how often the test correctly identifies those who have the virus, so a test with high sensitivity will not have many false-negative results. Studies suggest that sensitivity may be somewhere between 85% and 98%. A recent study considering tests in the Lighthouse labs estimated that this is most likely to be around 95%. Test specificity measures how often the test correctly identifies those who do not have the virus, so a test with high specificity will not have many false-positive results. We know the specificity of our test must be very close to 100% as the low number of positive tests in our study over the summer of 2020 means that specificity would be very high even if all positives were false. You can find more information on sensitivity and specificity in our COVID-19 Infection Survey methods article and our blog that explains why we trust the data from the COVID-19 infection survey.
Real-time reverse transcriptase polymerase chain reaction tests (RT-PCR) are used to test for the presence of SARS-CoV-02, the virus that causes coronavirus (COVID-19). This is an accredited test that is part of the national testing programme. You can find more information about processing our data using the RT-PCR in our methods article.
For further information and an overview of all the data published across the ONS, please check our ONS COVID Insights Tool.