COVID-19-like symptoms and their relation to the SARS-CoV-2 epidemic in children and adults of an Italian birth cohort

to estimate the population prevalence of COVID-19-like symptoms in children and adults during the first SARS-CoV-2 epidemic wave hitting Italy in the spring 2020; to assess their geographical correlation with the cumulative number of COVID-19 cases by province; to analyse their clustering within families; to estimate their sensitivity, positive predictive value (PPV) and negative predictive value (NPV) for COVID-19 diagnosis in individuals tested for SARS-CoV-2. cross-sectional study nested within a birth cohort. mothers participating in an Italian birth cohort (NINFEA) were invited to complete an online questionnaire on COVID-19-like symptoms in their household. population prevalence of COVID-19-like symptoms in children and adults, geographical correlation of COVID-19-like symptoms with the cumulative number of COVID-19 cases by province, clustering of COVID-19-like symptoms within families, and sensitivity, PPV and NPV of COVID-19-like symptoms for COVID-19 diagnosis in individuals tested for SARS-CoV-2. information was collected on 3,184 households, 6,133 adults, and 5,751 children. In the period March-April 2020, 55.4% of the NINFEA families had at least one member with at least one COVID-19-like symptom. There was a strong geographical correlation between the population cumulative incidence of COVID-19 and the prevalence of muscle pain, fatigue, low-grade fever, and breathing difficulties in adults (Spearman's rho >=0.70). Having at least one family member with a COVID-19 diagnosis, compared with none tested for SARS-CoV-2, was associated with an increased prevalence ratio (PR) of almost all COVID-19-like symptoms in adults, and only of low-grade fever (37-37.5°C; PR 4.54; 95%CI 2.20-9.40) and anosmia/dysgeusia in children. Among adults with COVID-19 diagnosis, fatigue, muscle pain, and fever had a sensitivity >=70%. In individuals tested for SARS-CoV-2, with a 16.6% prevalence of COVID-19, breathing difficulties and nausea/vomiting had the highest PPVs, with point estimates close to 60%, and with NPVs close to 90%. the geographical prevalence of COVID-19-like symptoms in adults may inform on local disease clusters, while certain symptoms in family members of confirmed COVID-19 cases could help identify the intra-familial spread of the virus and its further propagation in the community. Low-grade fever is frequent in children with at least one household member with COVID-19 and possibly indicates child infection.