Social, demographic and behavioural determinants of SARS-CoV-2 infection: A case-control study carried out during mass community testing of asymptomatic individuals in South Wales, December 2020
Authors: Thomas Daniel Rhys , Fina Laia Homar , Adamson James P. , Sawyer Clare , Jones Angela , Nnoaham Kelechi , Barrasa Alicia , Shankar A. Giri , Williams Chris J. 
Published: April 2021

Background

Between 21 November and 22 December 2020, a SARS-CoV-2 community testing pilot took place in the South Wales Valleys. Lateral flow tests were offered to all people aged over 10 years living, studying or working in the area.

Methods

We conducted a case-control study in adults taking part in the pilot using an anonymous online questionnaire. Social, demographic and behavioural factors were compared in people with a positive test (cases) and a sample of negatives (controls). Population attributable fractions (PAF) were calculated for factors with significantly increased odds following multivariate analysis.

Results

A total of 199 cases and 2,621 controls were recruited by SMS (response rates: 27.1% and 37.6% respectively). Following adjustment, cases were more likely to work in the hospitality sector (aOR: 3.39, 95% CI: 1.43-8.03), social care (aOR: 2.63, 95% CI: 1.22-5.67) or healthcare (aOR: 2.31, 95% CI: 1.29-4.13), live with someone self-isolating due to contact with a case (aOR: 3.07, 95% CI: 2.03-4.62), visit a pub (aOR: 2.87, 95% CI: 1.11-7.37), and smoke or vape (aOR: 1.54, 95% CI: 1.02-2.32). In this community, and at this point in the epidemic, reducing transmission from a household contact who is self-isolating would have the biggest public health impact (PAF: 0.2).

Conclusion

Infection prevention and control should be strengthened to help reduce household transmission. As restrictions on social mixing are relaxed, hospitality venues will become of greater public health importance, and those working in this sector should be adequately protected. Smoking or vaping may be an important modifiable risk factor.

What is already known on this subject?

Certain populations are known to be at risk of severe COVID-19: Older people, males, people in minority ethnic groups, people with pre-existing chronic disease or disability, and people in certain public-facing occupations. However, limited information exists on the factors associated with acquiring SARS-CoV-2 in the community.

What this study adds?

This study provides an insight into the most important factors determining community transmission of SARS-CoV-2. We found that transmission within the household was the most important source of SARS-CoV-2 infection. Working in the hospitality sector, and visiting the pub were associated with infection but at the time of this study were relatively infrequent exposures. Smoking or vaping had a small but significant effect. Working in education, living with someone working in education, having caring responsibilities, attending a healthcare appointment and visiting a supermarket, restaurant, gym or leisure centre were not associated with infection. Whilst these findings relate to a specific community at a specific time in the course of the epidemic when social restrictions were in place, the information will be useful in supporting policy decisions. Mass testing exercises present an opportunity to conduct epidemiological studies to gather information to inform the local and national epidemic response.