The investigators are conducting a national COVID-19 prevalence survey on a sample of 3,000
inhabitants that we have randomly selected from the Slovenian population. The sample is
representative in age, gender, and geographical distribution.

The main objective is to assess how many people in Slovenia have COVID-19 in April/May 2020
and how many were infected with SARS-CoV-2 previously.

Direct detection of SARS-CoV-2 RNA in nasopharyngeal samples is performed with validated
two-target PCR-based commercial assay. For a serological response to the etiological agent,
IgG and IgA anti-SARS-CoV-2 antibodies are measured in plasma samples using a validated
commercial assay.

Principal aims of the study are to systematically and accurately assess:

- How many people in Slovenia are actively infected with SARS CoV-2 in April/May 2020?

- How many are asymptomatic and do not even know they are or were infected?

- How many people in Slovenia have contacted SARS-CoV-2 and already have COVID-19 until
mid May 2020?

The study is carried out by the Institute of Microbiology and Immunology of University of
Ljubljana. The Institute is Slovenia's leading institution for microbiology and immunology
research. The study is joined by a team of IT specialists, data scientists, and statisticians
from the other departments of the University of Ljubljana.

To speed-up and support the study, an innovative information infrastructure for data
gathering and management was purposely developed and optimized for the study. The system
fosters error-free data collection, automatic processing of questionnaires using artificial
intelligence approaches, and provides security for sensitive clinical data.

All participants will be passively followed up twice monthly and tested again for the
presence of anti-SARS-CoV-2 antibodies in plasma samples six months after enrollment.