AbstractBackgroundTo rapidly characterize COVID-19 epidemiology, numerous population-based studies have been undertaken to model the risk of SARS-CoV-2 infection. Less is known about what may drive the probability to undergo testing. Understanding how much testing is driven by contextual or individual conditions provides the basis for unbiased representation of testing figures and shaping of public health interventions and resource allocation.MethodsIn the Val Venosta/Vinschgau district (South

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... yrol, Italy), we conducted a population-representative longitudinal study on 697 individuals who completed 4,512 repeated online questionnaires at four week intervals between September 2020 and May 2021. Mixed-effects logistic regression models were fitted to investigate associations between self-reported SARS-CoV-2 testing and both individual characteristics (social, demographic, and biological) and contextual determinants.ResultsTesting was associated with month of reporting, reflecting the timing of both the pandemic intensity and public health interventions, COVID-19-related symptoms (odds ratio, OR:8.26; 95% confidence interval, CI:6.04–11.31), contacts with infected individuals within home (OR:7.47, 95%CI:3.81–14.62) or outside home (OR:9.87, 95%CI:5.78–16.85), and being retired (OR:0.50, 95%CI:0.34-0.73). Within- and outside-home contacts were the leading determinants in the first and second half of the period, respectively, possibly reflecting later relaxation of social-distancing measures. Testing was not associated with age, sex, education, comorbidities, or lifestyle factors.ConclusionsIn the study area, contextual determinants reflecting the course of the pandemic were predominant compared to individual sociodemographic characteristics in explaining the SARS-CoV-2 probability testing. Decision makers should evaluate whether the intended target groups were correctly prioritized by the testing campaign.Research in Context box for Lancet Regional Health – EuropeEvidence before this studySince the beginning of the COVID-19 pandemic, characterizing the epidemiological landscape of SARS-CoV-2 infections was an urgent need. Numerous population-based studies were undertaken to quantify infection risk. However, while such quantification critically depends on the availability and accessibility of swab tests, studies assessing SARS-CoV-2 nasopharyngeal swab-testing probability at population level are lacking. A PubMed search for "COVID-19" or "SARS-CoV-2" and "testing" and "probability" or "determinants", conducted on November 30, 2021, identified few, mostly non-European cross-sectional studies revealing that access to COVID-19 testing can be associated with deprivation, ethnicity, and age. A comprehensive assessment of how much testing might be driven by contextual rather than personal conditions is currently missing. This appears to be particularly relevant since, during the pandemic, the personal conduct of citizens, which depends on biological, social and cultural factors, seems to have played a role in various circumstances such as willingness to be tested or to be vaccinated. We addressed this question by investigating data from the CHRIS COVID-19 study, a rural population-based study that collected information on SARS-CoV-2 testing as well as biological, sociodemographic, lifestyle-related, and medical conditions from each participant longitudinally between September 2020 and May 2021.Added value of this studyIn the studied region, which is ethnically and culturally more homogeneous than most other study contexts, contextual determinants reflecting the course of the pandemic and individual sociodemographic characteristics were assessed as determinants for undergoing testing. The only factors suggested to be associated with SARS-CoV-2 testing were the time period, presence of symptoms, and contacts with infected or symptomatic individuals within- and outside-home. The time period reflects the temporal evolution of the pandemic and mitigation policies. Contacts with other individuals reflect the social context, with stronger association found for within-home contact earlier in the period, when infection rates were higher and restrictions on social contact more rigid, and for outside-home contact later. When these factors were accounted for, no personal characteristic was associated with the probability to undergo a swab test, except being retired, which was associated with a lower probability of getting tested, probably because of the greater isolation of this group.Implications of all the available evidenceThe study shows that, in this area, individuals largely followed the general recommendations for undertaking a test when they had symptoms and contacts with infected individuals. The study also implicates that citizens undertook SARS-CoV-2 testing regardless of their personal demographic, economic, cultural and medical condition. This could be reassuring to the healthcare system in terms of social equity. On the other hand, decision makers should evaluate whether the specific target groups, such as individuals with higher risk to develop severe COVID-19 disease, were correctly prioritized by the testing campaign, especially during the acute phase of the pandemic. Further research is needed to investigate additional reasons potentially related to SARS-CoV-2 testing, such as information about testing center accessibility or limited laboratory resources.