EPICOVID19: Psychometric assessment and validation of a short diagnostic scale for a rapid Covid-19 screening based on reported symptoms
Authors: Bastiani Luca , Fortunato Loredana , Pieroni Stefania , Bianchi Fabrizio , Adorni Fulvio , Prinelli Federica , Giacomelli Andrea , Pagani Gabriele , Maggi Stefania , Trevisan Caterina , Noale Marianna , Jesuthasan Nithiya , Sojic Aleksandra , Pettenati Carla , Andreoni Massimo , Incalzi Raffaele Antonelli , Galli Massimo , Molinaro Sabrina 
Published: July 2020

Background

Confirmed COVID-19 cases have been registered in more than two hundred countries and regions and of July 28 over 16 million cases of COVID-19, including 650805 deaths, have been reported to WHO. 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 Italian 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<0.0001), Loss of Taste and/or Smell (365 [52.6%] vs 239 [11.9%]; p<0.0001) and Cough (352 [50.7%] vs 580 [28.9%]; p<0.0001). Also for other symptoms the frequencies were significantly higher in NPS(+) subjects than in NPS(-) ones (p<0.001). Among groups with serological tests, the symptoms with higher percentages in the subjects IgG(+) were Fever (65 [60.2%] vs 43[11.8%]; p<0.0001) and Pain in muscles, bones, joints (73 [67.6%] vs 71 [19.5%]; p<0.0001). For the COVID-19 self-reported symptoms items, exploratory (proportion variance explained [89.9%]) and confirmatory factor analysis results (SMSR 0.072; RMSEA 0.052) highlights the presence of one latent variable (factor) underlying the symptoms. We define the one-factor solution as EPICOVID19 diagnostic scale and optimal score for each items was identified: Respiratory problems (1.03), Chest pain (1.07), Loss of Taste and/or Smell (0.97) and Tachycardia (palpitations) (1.05) were the most important symptoms.

The cut-off score was 2.56 (Sensitivity 76.56%; Specificity 68.24%) in NPS(+) and 2.59 (Se 80.37; Sp 80.17) in IgG(+) subjects.

Interpretation

We developed a short diagnostic scale to detect subjects with symptoms potentially associated with COVID-19 among a wide population. Early recognition screening and rapid diagnosis are essential to prevent transmission and provide supportive care in a timely manner and our score supports the potential for identifying individuals who need to seek immediate clinical evaluation. Although these results are referred to the Italian pandemic period, this short diagnostic scale could be optimised and tested as a screening tool in other similar pandemic contexts.