Coronavirus (COVID-19): ONS Infection Survey results – characteristics data – symptoms analysis – 5 May 2021

The article is based on findings from the Office for National Statistics (ONS) COVID-19 Infection Survey.

The COVID-19 Infection Survey aims to measure:

• how many people test positive for COVID-19 infection at a given point in time, regardless of whether they report experiencing coronavirus symptoms
• the average number of new infections per week over the course of the study
• the number of people who test positive for antibodies, to indicate how many people are ever likely to have had the infection or have been vaccinated

The results are for private households only, and do not apply to those in hospitals, care homes or other institutional settings. The population used in this analysis relates to the community population aged two years and over.

The Office for National Statistics (ONS) publish analysis of the characteristics of those testing positive for COVID-19 in England, Wales, Northern Ireland, Scotland and the UK on their website.

The underlying data displayed in the charts in this publication is available in the reference tables on the ONS website.

Main points

In the community population in Scotland, 55.3% of people who tested positive for COVID-19 with a strong positive test between 1 December 2020 and 4 April 2021 reported having any symptoms (95% Confidence Interval: 49.7% to 60.8%).  

Symptom profile of people who tested positive for COVID-19

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.

Participants who only have positive tests with these high values are excluded from this analysis to exclude the possibility that symptoms are not identified because we pick up individuals very early or later on in their infection. You can find more information on Ct values in a paper written by academic partners at the University of Oxford.

This analysis considers individuals with any positive test (including repeated positive tests) that had a Ct value less than 30 between 1 December 2020 and 4 April 2021 . This analysis considers all symptoms reported at visits within 35 days of the first positive test of the episode, and at each visit participants are asked about their symptoms in the last seven days. This includes symptoms reported even when there is a negative test within this timeframe or a positive test with a higher Ct value. The methodology has changed since this analysis was last published, more details on the method used can be found on the ONS website. 

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.

In the community population in Scotland, 55.3% of people who tested positive for COVID-19 with a strong positive test between 1 December 2020 and 4 April 2021 reported having any symptoms (95% Confidence Interval: 49.7% to 60.8%).  

Over half the people who are estimated to have tested positive for COVID-19 with a strong positive test reported having some symptoms within 35 days of the test in England, Wales and Scotland.

Results should be interpreted with caution for Scotland, Wales and Northern Ireland because of smaller sample sizes of people who have a strong positive test (Ct less than 30) than for England, resulting in wider confidence intervals.

Figure 1: Percentage of people who tested positive for COVID-19 who reported having any symptoms and no symptoms, in each of the four nations of the UK, from 1 December 2020 to 4 April 2021 including 95% confidence intervals

Figure 2 shows that people who tested positive for COVID-19 with a strong positive test were more likely to report ‘classic’ Covid-19 symptoms (cough, fever, loss of taste or loss of smell) than gastrointestinal or loss of taste or smell only.

Figure 2: Percentage of people with symptoms, by symptom category, including only those who have strong positive tests (Ct less than 30), from 1 December 2020 to 4 April 2021 in Scotland, including 95% confidence intervals

Figure 3 shows that fatigue, headache and cough were the most common symptoms reported in strong positive COVID-19 cases in Scotland. Abdominal pain, diarrhoea and nausea or vomiting were less commonly reported symptoms in strong positive COVID-19 cases. Similar patterns in reported symptoms can be seen in all four UK countries.

Figure 3: Percentage of people with symptoms, including only those who have strong positive tests (Ct less than 30), from 1 December 2020 to 4 April 2021 in Scotland, including 95% confidence intervals

Further information and methodology notes

The results are for private households only, and do not apply to those in hospitals, care homes or other institutional settings. The population used in this analysis relates to the community population aged two years and over.

The full article was published by the Office for National Statistics on 5 May 2021, which includes data for England, Wales and Northern Ireland. The article also includes analysis on the likelihood of testing positive for COVID-19 by work location, mode of travel to work and reported ability to socially distance in the workplace in the UK.

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.

Methodology notes

1. 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.
2. 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.
3. The analysis is based on data collected at each study visit where participants are asked to report their symptoms in the previous 7 days.
4. The analysis shows the proportion of individuals testing positive who reported experiencing symptoms at study visits within 35 days of their first positive test.
5. Symptoms are self-reported and were not professionally diagnosed.
6. Because of the relatively small number of tests and a low number of positives in the sample, confidence intervals are wide and therefore results should be interpreted with caution.
7. SARS-CoV-2 is the scientific name given to the specific virus that causes COVID-19.
8. 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.