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This analysis looks at each person who tested positive for COVID-19 who had a strong positive test. The strength of the test is determined by how quickly the virus is detected, measured by a cycle threshold (Ct) value. The lower the Ct value, the higher the viral load and the stronger the positive test. Positive results with a high Ct value could be seen in the early stages of infection when virus levels are rising, or late in the infection, when the risk of transmission is low. These values are excluded from this analysis to exclude the possibility that symptoms are not identified when an individual tests positive, but it is very early on or later in their infection.
This analysis considers individuals with any positive test that had a Ct value less than 30, between 1 October 2020 and 30 January 2021, and considers what percentage of these individuals reported symptoms at visits within 35 days of a positive test.
Individuals taking part in the survey were asked at each visit whether they had experienced a range of possible symptoms in the seven days before they were tested and also separately whether they felt that they had symptoms compatible with COVID-19 infection in the last seven days.
Symptom profile of people who tested positive for COVID-19
It is estimated that, in Scotland, between 1 October 2020 to 30 January 2021, 47% of people who tested positive for COVID-19 with high Ct values reported having any symptoms. A 95% confidence interval for this figure is 41% to 54%.
Figure 1: Percentage of people who tested positive for COVID-19 who reported having any symptoms, in each of the four nations of the UK, including 95% confidence intervals
The most commonly reported symptoms, of those with high Ct values, are headache, cough and fatigue or weakness. The least common symptoms reported are abdominal pain and diarrhoea. The most and least commonly reported symptoms mentioned are consistent across Scotland, England, Wales and Northern Ireland.
Figure 2: Reported symptoms as a percentage of people who tested positive for COVID-19 in Scotland, including 95% confidence intervals
Methodology and further information
This analysis looks at symptoms associated with positive episodes (including repeated positive tests) with any Ct value in the episode below 30. This is to exclude the possibility that symptoms are not identified when an individual tests positive as it is very early on or later on in the infection.
The analysis is based on data collected at each study visit where participants are asked to report their symptoms in the previous 7 days.
The analysis shows the proportion of individuals testing positive who reported experiencing symptoms at study visits within 35 days of their first positive test.
Symptoms are self-reported and were not professionally diagnosed.
The population relates to the community population (private households) aged two years and over, and does not include people in hospital, care homes or students in halls of residence, where rates of COVID-19 infection are likely to be different.
SARS-CoV-2 is the scientific name given to the specific virus that causes COVID-19.
Estimates are provided with 95% confidence intervals to indicate the level of uncertainty around them. A confidence interval gives an indication of the degree of uncertainty of an estimate, showing the precision of a sample estimate. The 95% confidence intervals are calculated so that if we repeated the study many times, 95% of the time the true unknown value would lie between the lower and upper confidence limits. A wider interval indicates more uncertainty in the estimate.
The full article was published by the Office for National Statistics on 9 February, which includes data for England, Wales and Northern Ireland, can be accessed here.
More information about the COVID-19 Infection Survey in Scotland can be found on the information page on the Scottish Government website, and previous COVID-19 Infection Survey data for Scotland can be found in this collection.