Mass SARS-CoV-2 serological screening, a population-based study in the Principality of Andorra

Abstract

Background Andorra is a small country located in the Pyrenees attracting millions of visitors for tourism, mostly associated with skiing, and nature-related activities. As its neighbouring countries, Spain and France, it has been heavily affected by the COVID-19 pandemic. We estimated SARS-CoV-2 seroprevalence in the entire country by universal serological testing under a lockdown environment. Methods A total of 77,543 inhabitants of Andorra were invited to participate in the study. From 4-28 May, 2020, two cross sectional serological surveys were conducted using a rapid serological test (nCOV IgG/IgM) on a finger prick blood sample in 59 drive-through or walk-through checkpoints, all over Andorra. We calculated seroprevalence of antibodies against SARS-CoV-2 and analysed the main sociodemographic factors associated with being seropositive. Findings 70,494 inhabitants (90.9% of the population) participated in at least one survey. Overall seroprevalence was 11.0%. The most affected age groups were those over 90 years old (15.2%) and 80-89 (13.8%), followed by adults 50-59 (13.6%) and adolescents 10-19 (13.7%). Most seropositive participants, 6,061 (95.1%), were asymptomatic before the surveys. The multivariable analysis showed that the odds of being seropositive was higher among seasonal workers (OR 2.41; 95% CI 1.07-5.45) or in the population living in La Massana region, a popular ski-related area (OR 2.66; 95% CI 2.44-2.89). A higher seroprevalence was observed in those familiar nuclei with greater numbers of cohabitants: 18% in families with 6 household members or more; 13% in medium size families (3/4/5 people) and 12% in small size (1 to 2 people) nuclei. Interpretation The prevalence of antibodies against SARS-CoV-2 in the population of Andorra was high during the first wave of the pandemic. Seasonal workers and inhabitants based in La Massana presented a higher seroprevalence. Mass antibody screening allows to identify infection hotspots and should contribute to the design of tailored interventions to prevent SARS-CoV-2 transmission in Andorra. Funding Andorran Ministry of Health, Andorran Health Services.

Infection fatality rate of COVID-19 in community-dwelling elderly populations

“…Screening and exclusions are shown in Online Appendix Figure 1 and Online Appendix Table 3. Twelve seroprevalence studies were included, one of which contained two separate surveys; another 13 studies with convenience samples were considered in sensitivity analysis [ 33 , 34 , 35 , 36 , 37 , 38 , 39 , 40 , 41 , 42 , 43 , 44 , 45 , 46 , 47 , 48 – 56 ].…”

Using mobile phone data to estimate dynamic population changes and improve the understanding of a pandemic: A case study in Andorra

“…The program was conducted for a previous research study, in which the methods and results are detailed [32]. The study was approved by the Institutional Review Board of the Servei Andorra Atencio Sanitaria (register number 0720).…”

“…Data for temporary workers is highlighted. Seroprevalence data is from previously reported results and was calculated based on the number of individuals who had a positive result of IgG and/or IgM [32]. The testing was voluntary; an issue with the testing was that many people who participated in the first survey did not participate in the second survey.…”

“…Note that the sum of survey participation varies due to missing values regarding the participants' parish of residence or temporary worker status. Two cross sectional serological surveys were conducted in Andorra from May 4-28, 2020, using a rapid serological test (nCOV IgG/IgM) [32]. For each participant, the test data include the dates of their participation in surveys 1 and/or 2, the positive versus negative results for IgG/IgM antibodies for each round of testing, the participant's parish of residence, whether the participant is a temporary worker, and other demographic information.…”

“…In May of 2020, Andorra conducted a nationwide serology testing program. This resulted in the first published seroprevalence study universally testing the entire population of a country and one of the largest of its kind [32]. Anyone over the age of 2 was invited to participate in the study, including the country’s temporary workers.…”