Individuals were identified through the Epidemiological Surveillance Emergency Service of Catalonia (SUVEC), an electronic registry that is notified of all regional COVID-19 cases. 293 participants were eligible for the study (non-hospitalized individuals, <5 days since symptom onset) and randomly selected by a computer generator for either HCQ intervention or control arm. 136 were assigned HCQ and 157 assigned no antiviral treatment (not-placebo controlled). 800 mg of HCQ was administered on day 1, with an additional 400 mg/day for 6 days). Nasopharyngeal and serial oral swabs were collected on days 1, 3, and 7.