A pilot study of PCR community mass testing for COVID-19: who attends and who tests positive?

BACKGROUND: PCR community mass testing for COVID-19 was delivered in three sites in Greater Glasgow and Clyde with high incidence of COVID-19, between Nov 30 and Dec 9, 2020. The purpose of mass testing was active case finding in communities. The aim of the study was to examine who attends mass testing and who tests positive, and how this differs from regular testing where only asymptomatic people attend. METHODS: χ(2) tests compared age, sex, deprivation, and ethnicity data collected from the three sites with target population Ward profile data published by Glasgow City Council for each site. Regular symptomatic test data for a period before and after the mass testing period were also analysed (Sept 1–Nov 29, 2020, and Dec 11–15, 2020). Data were modelled using logistic regression for outcome test result (positive vs negative or void) for mass and regular testing datasets. Demographic variables, as well as symptomatic or asymptomatic were included in the model. Modelling of the dataset combining mass and regular testing included interaction terms to detect differences in determinants between testing methods. FINDINGS: 7497 PCR tests were done. There was under-representation in attendance of more deprived quintiles (p<0·0001 under a χ(2) test), Black or minority ethnic groups (p<0·0001), males (p=0·039), older people (≥65 years; p=0·012), and children (<16 years; p=0·0062). Two of the sites had a high proportion of symptomatic cases (1331 [31%] and 1939 [65%]), for whom the percentage positive was substantially higher (203 [15·3%] and 229 [11·8%]) than asymptomatic individuals (76 [2·6%] and 39 [3·7%]; p<0·0001). Multivariable modelling found that increasing age (odds ratio 4·64 [95% CI 1·95–11·06] for 45–64 years [3·77, 1·59–8·93 for 30–44 years] compared with 0–4 years), ethnicity (1·98 [1·19–3·29] for Asian compared with White) and symptoms (4·59 [3·09–6·83] for symptoms vs no symptoms) were significantly associated with testing positive in mass testing. When test data were modelled simultaneously, an interaction term found females, Africans, and people who identified as other ethnic background were significantly more likely to test positive in mass testing compared with regular testing. INTERPRETATION: Some groups were under-represented in PCR community mass testing. Specifically, people living in more deprived areas, ethnic groups, older people, and children were less likely to attend a mass testing site. Adults, older people, and ethnic minority groups were more likely to test positive, and testing of symptomatic individuals, as well as asymptomatic individuals, would maximise case finding. FUNDING: None.