ABSTRACT
Digital technologies have been extensively employed in response to the SARS-CoV-2 pandemic worldwide. This study describes the methodology of the two-phase internet-based EPICOVID19 survey, and the characteristics of the adult volunteers respondents who lived in Italy during the first (April - May 2020) and the second wave (January - February 2021) of the epidemic. Validated scales and ad-hoc questionnaires were used to collect socio-demographic, medical and behavioural characteristics, as well as information on COVID-19. Among those who provided email addresses during phase I (105,355), 41,473 participated in phase II (mean age 50.7 years +/- 13.5 SD, 60.6% females). After a median follow-up of ten months, 52.8% had undergone naso-pharyngeal swab (NPS) testing and 13.2% had positive result. More than 40% had undergone serological test (ST) and 11.9% were positive. Out of the 2,073 participants with at least one positive ST, 72.8% had only negative results from NPS or never performed it. These results indicate that a large fraction of individuals remained undiagnosed, possibly contributing to the spread of the virus in the community. Participatory online surveys offer a unique opportunity to collect relevant data at individual level from large samples during confinement.