This simple question is quite difficult to answer. Taking the UK as an example, the daily statistics released by the UK government only include people who have been tested because they have been in hospital with symptoms, or because they are essential workers with symptoms, or care home residents. Most people outside of hospitals or care homes are not tested.

The best estimate we have of how many people in the community are infected is from an Office for National Statistics (ONS) pilot study. So far 14,599 people from 7,054 households in England were tested between 4th May and 17th May.

In the study, 35 people from 32 households tested positive for SARS-CoV-2, the virus that causes COVID-19. Using these findings, the researchers calculated that 0.25% of the population of England (outside of hospitals and care homes) had SARS-CoV-2 at this time. That’s about 1 new infection per 1,000 people each week.

Where did the story come from?

The initial results of the ongoing ONS study (which gave a slightly higher figure of 0.27% of the population currently infected) were covered by BBC News, among others. Their head of statistics said that the figure might seem “surprisingly small”. However, he pointed out that 0.27% amounted to about 150,000 people in England.

What is the basis for the claim?

The ONS study is the first time a big sample of the general population of England has been tested for SARS-CoV-2. The study involved people who had previously volunteered to take part in ONS research, so was not a completely random sample.

The researchers asked 20,000 households in England to take part in the study. So far 7,054 households have performed nose and throat swabs for everyone aged over 2 years in the household.

People were also asked about their occupation, whether they had any symptoms of COVID-19, whether they are self-isolating or shielding, and whether they have come into contact with anyone they suspect may have had COVID-19.

The study found that the proportion of people testing positive did not vary according to age, sex or whether people were working in healthcare or social care, seeing patients or care home residents or not.

The study did not include anyone living in a care home or currently in hospital. It provides only a snapshot of who was infected at the time of the tests, so does not tell us how many people in England have had the virus and recovered.

The study hopes to recruit 10,000 households, and there are plans to expand it to Scotland, Northern Ireland and Wales. After the initial swabs, households are invited to provide weekly swabs for 5 weeks and then monthly for 12 months. A proportion of participants will also have blood tests for antibodies to the virus, which may help discover how many people have had the virus in total.

What do trusted sources say?

Martin Hibberd, Professor of Emerging Infectious Disease at the London School of Hygiene & Tropical Medicine, said via the Science Media Centre: “The release of this data is a welcome step forward in understanding the SARS-CoV-2 outbreak. Going forward this will allow us to track a population-based estimate of the number of cases.”

Citation

Office for National Statistics. Statistical bulletin: Coronavirus (COVID-19) Infection Survey pilot: England, 21 May 2020. https://www.ons.gov.uk/peoplepopulationandcommunity/healthandsocialcare/conditionsanddiseases/bulletins/coronaviruscovid19infectionsurveypilot/england21may2020 (Accessed 26 May 2020).

Reading list

Science Media Centre. Expert reaction to first data from the ONS COVID-19 Infection Survey pilot, estimating numbers of people currently testing positive (swab ‘have-you-got-it’ test). https://www.sciencemediacentre.org/expert-reaction-to-first-data-from-the-ons-covid-19-infection-survey-pilot-estimating-numbers-of-people-currently-testing-positive-swab-have-you-got-it-test/ (Accessed 20 May 2020).