Patient characteristics
The COVID-19 patients were administered an approved questionnaire upon enrolment to collect information regarding COVID-19-related symptoms prior to hospitalization and smoking behaviours. The date of COVID-19 diagnosis, highest level of care received, the maximum amount of oxygen supplementation required (unit, oxygen need 5L/min supplemented by High Flow Nasal Oxygen (HFNO) or Continuous Positive Airway Pressure (CPAP)), and the critical care provided (intensive care unit, with or without mechanical ventilation) for COVID-19 illness were all gathered from digital medical records.