Self-reported symptoms of SARS-CoV-2 infection in a non-hospitalized population : results from the large Italian web-based EPICOVID19 cross-sectional survey. (Preprint)

Background: Understanding the occurrence of Severe Acute Respiratory Syndrome-Coronavirus-2 (SARS-CoV-2)-like symptoms in a large non-hospitalized population, when the epidemic peak was occurring in Italy, is of paramount importance but data are scarce. Objective: Aims of this study were to evaluate the association of self-reported symptoms with SARS-CoV-2 nasopharyngeal swab (NPS) test in non-hospitalized individuals and to estimate the occurrence of COVID-19-like symptoms in a larger non-tested population. Methods: This is an Italian countrywide self-administered cross-sectional web-based survey on voluntary adults who completed an anonymous questionnaire in the period 13-21 April 2020. The associations between symptoms potentially related to SARS-CoV-2 infection and NPS results were calculated as adjusted odds ratios with 95% confidence intervals (aOR, 95%CI) by means of multiple logistic regression analysis controlling for age, sex, education, smoking habits, and the number of co-morbidities. Thereafter, for each symptom and for their combination, we calculated sensitivity, specificity, accuracy and AUC in a ROC analysis to estimate the occurrence of COVID-19-like infections in the non-tested population. Results: A total of 171,310 responded to the survey (59.9% females, mean age 47.4 years). Out of the 4,785 respondents with known NPS test result, 4,392 were not hospitalized. Among them, the NPS positive respondents (n=856) most frequently reported myalgia (61.6%), olfactory and/or taste disorders (OTDs, 59.2%), cough (54.4%), and fever (51.9%) whereas 7.7% were asymptomatic. Multiple regression analysis showed that OTDs (aOR 10.3, [95%CI 8.4-12.7]), fever (2.5, 95%CI 2.0-3.1), myalgia (1.5, 95%CI 1.2-1.8), and cough (1.3, 95%CI 1.0-1.6) were associated with NPS positivity. Having two to four of these symptoms increased the aOR from 7.4 (95%CI, 5.6-9.7) to 35.5 (95%CI, 24.6-52.2). The combination of the four symptoms showed an AUC of 0.810 (95%CI 0.795-0.825) in classifying NPS-P, and was applied to the non-hospitalized and non-tested sample (n=165,782). We found that from 4.4% to 12.1% of respondents had experienced symptoms suggestive of COVID-19 infection. Conclusions: Our results suggest that self-reported symptoms may be reliable indicators of SARS-CoV-2 infection in a pandemic context. A not negligible part (up to 12.1%) of the symptomatic respondents were left undiagnosed and potentially contributed to the spread of the infection.