Amanda Mocroft and colleagues investigate risk factors and health outcomes associated with diagnosis at a late stage of infection in individuals across Europe. Please see later in the article for the Editors' Summary

BACKGROUND No therapeutics have yet been proven effective for the treatment of mild-illness caused by SARS-CoV-2. We aimed to determine whether early treatment with hydroxychloroquine (HCQ) would be more efficacious than no-treatment for outpatients with mild Covid-19. METHODS We conducted a multicenter, open label, randomized controlled trial in Catalonia (Spain) between March 17, and May 26, 2020. Eligible Covid-19 cases were non-hospitalized adult patients with recently confirmed SARS-CoV-2 infection and less than five days of symptoms. Patients were assigned to receive HCQ (800 mg on day 1, followed by 400 mg once daily for 6 days) or no antiviral treatment (not-placebo controlled). Study outcomes were the reduction of viral RNA load in nasopharyngeal swabs up to 7 days after treatment start, patient disease progression using the WHO scale up to 28 days, and time to complete resolution of symptoms. Adverse events were assessed up to 28 days. RESULTS A total of 293 patients were eligible for intention-to-treat analysis: 157 in the control arm and 136 in the intervention arm. The mean age was 41.6 years (SD 12.6), mean viral load at baseline was 7.90 (SD 1.82) Log10 copies/mL, and median time from symptom onset to randomization was 3 days. No significant differences were found in the mean reduction of viral load at day 3 (-1.41 vs. -1.41 Log10 copies/mL in the control and intervention arm, respectively; difference 0.01 [95% CI -0.28;0.29]) or at day 7 (-3.37 vs. -3.44; d –0.07 [-0.44;0.29]). This treatment regimen did not reduce risk of hospitalization (7.1%, control vs. 5.9%, intervention; RR 0.75 [0.32;1.77]) nor shortened the time to complete resolution of symptoms (12 days, control vs. 10 days, intervention; p = 0.38). No relevant treatment-related AEs were reported. CONCLUSIONS In patients with mild Covid-19, no benefit was observed with HCQ beyond the usual care.