EPICOVID19: Psychometric assessment and validation of a short diagnostic scale for a rapid Covid-19 screening based on reported symptoms

Background Confirmed COVID-19 cases have been reported in 213 countries and regions and as of 12 July 2020, over 12 million cases, with 561617 deaths have been reported worldwide. The number of cases changes quickly and varies depending upon which source you use to track, so in the current epidemiological context, the early recognition is critical for the rapid identification of suspected cases (with SARS-CoV-2 infection-like symptoms and signs) to be immediately subjected to quarantine measures. Although surveys are widely used for identifying COVID-19 cases, outcomes and associated risks, no validated epidemiological tool exists for surveying SARS-CoV-2 infection in the population so far. Methods Our study is the phase II of the EPICOVID19 national survey, launched in April 2020 including a national convenience sample of 201121 adults, who voluntarily filled the EPICOVID19 questionnaire. The phase II questionnaire was mailed to all subjects who underwent tests for COVID-19 by nasopharyngeal swab (NPS) and who accepted to be involved in the second phase of the study, focused on the results reported for NPS and/or serological IgG/IgM tests. We evaluated the capability of the self-reported symptoms collected through the EPICOVID19 questionnaire to discriminate the COVID-19 among symptomatic subjects, in order to identify possible cases to undergo instrumental measurements and clinical examinations. We defined a method for the identification of a total score and validated it with reference to the serological and molecular clinical diagnosis, using four standard steps: identification of critical factors, confirmation of presence of latent variable, development of optimal scoring algorithm and validation of the scoring algorithm. Findings 2703 subjects [66% response rate] completed the Phase II questionnaire. Of 2703 individuals, 694 (25.7%) were NPS(+) and of these 84 (12.1% of the 694 NPS(+)) were asymptomatic. In the individuals who performed serological testing, of the 472 who did IgG(+) and 421 who did IgM(+), 22.9% and 11.6% tested positive, respectively. Among IgG(+) 1 of 108 subjects was asymptomatic (0.9%) while 5/49 subjects among IgM(+) were asymptomatic (10.2%). Compared with NPS(-), among NPS(+) subjects there was a higher rate for Fever (421 [60.7%] vs 391[19.5% ]; p