Risk stratification of COVID-19 patients is essential to define their appropriate treatment setting. So far, available studies have focused on morbidity and mortality prediction in patients admitted to hospital. In the Emergency Department (ED), decision on home discharge versus hospital admission for COVID-19 is cumbersome. While facing a dramatic second wave of SARS-CoV-2, shortage of hospital beds has further increased the challenge.

The present study will prospectively evaluate the clinical outcomes of patients discharged from the ED. Stratification will be based on a composite of demographic, clinical and lung imaging variables. Results will be used to develop standardized decision rules for safe home discharge of patients with COVID-19 evaluated in the ED.

Patients with inclusion criteria and without exclusion criteria, evaluated in the participating EDs, will be enrolled in the study. Patients will undergo standard medical evaluation by the attending physician(s), following local guidelines and best medical practice, independent of participation to the study.

The following data will be recorded, when available:

• Demographic/clinical: age, gender, symptoms (type, time from onset), comorbidities, Glasgow Coma Scale score, respiratory rate, peripheral oxygen saturation
• Biochemical: urea, creatinine, C-reactive protein, procalcitonin, lactate dehydrogenase, white blood cell count, lymphocyte count, d-dimer
• Lung ultrasonography: site/type of B lines, consolidations, pleural effusion
• Radiology: chest X-ray result, chest CT result

Upon discharge, patients will be encouraged to contact emergency medical services or return the ED if needed, in case of clinical worsening.

The following endpoint will be assessed at 30 days after ED discharge, through standardized telephone interview and healthcare/other database query: any further hospital admission (for COVID-19 or other disease), death (for COVID-19 or other disease), respiratory failure/ventilation/intensive care admission (only for hospitalized COVID-19 patients).

Data analysis will focus on the outcome incidence in the study cohort, stratified by a composite of demographic/clinical, biochemical and imaging variables. A key stratification tool will be the 4C mortality score (BMJ 2020; 370 doi: https://doi.org/10.1136/bmj.m3339). Additional integration of study variables will be evaluated to improve stratification and prediction.

Inclusion Criteria:

• symptomatic COVID-19 confirmed by treating physician
• positive nasopharyngeal swab for SARS-CoV-2 (performed during the ED visit or within last 14 days)
• First ED visit for suspected or confirmed COVID-19 (within last 30 days)
• Home discharge from ED based on treating physician's or patient's decision

Exclusion Criteria:

• Age <18 years
• Nursing home resident
• Already on home oxygen therapy
• Previous ED visit for suspected or confirmed COVID-19 (within last 30 days)
• Informed consent denial
• Follow-up not feasible

Adult patients (>18 years) subjected to a first ED visit for physician-confirmed COVID-19, discharged from the ED based on attending physician's or patient's decision (independent from study participation). Patients will provide their informed consent to participation (thus allowing clinical data recording and 30-day follow-up).