Abstract: Brazilian Journal of Microbiology (2020) 51:1765–1769 https://doi.org/10.1007/s42770-020-00395-x CLINICAL MICROBIOLOGY - RESEARCH PAPER No benefit of hydroxychloroquine on SARS-CoV-2 viral load reduction in non-critical hospitalized patients with COVID-19 Klinger Soares Faíco-Filho 1 & Danielle Dias Conte 1 & Luciano Kleber de Souza Luna 1 & Joseane Mayara Almeida Carvalho 1 & Ana Helena Sitta Perosa 2 & Nancy Bellei 1 Received: 4 August 2020 / Accepted: 21 October 2020 / Published online: 27 October 2020 # Sociedade Brasileira de Microbiologia 2020 Abstract Background Some studies have shown that hydroxychloroquine (HCQ) is an effective drug in reducing the in vitro replication of SARS-CoV-2. However, the in vivo effect of HCQ still unclear. Objectives This study aims to evaluate viral load clearance in patients with COVID-19 who underwent HCQ treatment in comparison with a control group that did not receive the drug. Study design This prospective study comprised consecutive viral load measurements in patients with COVID-19 hospitalized with a moderate illness. Patients received 400 mg of HCQ every 12 h for 10 days according to the medical decision. Nasal swab samples were collected from patients during early, intermediary, and final clinical stage of COVID-19. Results A total of 155 samples were collected from 66 patients with COVID-19 (60% female), with a median age of 58 years. The viral load between studied groups, assumed as a semiquantitative measure of cycle threshold (Ct) values, presented no significant difference within the three consecutive measures (ΔCt) (p > 0.05). We also analyzed the ΔCt viral load at different intervals of sample collection (Δt < 7; 7–12; and > 12 days) without significant differences at any ΔCt (p > 0.05). Conclusion In this study, we did not observe any change in viral load reduction in vivo with the use of HCQ. Keywords Viral load . SARS-CoV-2 . Hydroxychloroquine . COVID-19 Background On March 11, 2020, the World Health Organization (WHO) declared the novel severe acute respiratory syndrome coronavirus (SARS-CoV-2), responsible for the coronavirus disease of 2019 (COVID-19), a pandemic, when the virus reached five continents [1]. Since then, several medications have been tested in the treatment of this disease such as hydroxychloroquine (HCQ) [2], tocilizumab [3, 4], remdesivir [5], and heparin [6]. Responsible Editor: Mauricio Nogueira. * Klinger Soares Faíco-Filho klingerfaiko@hotmail.com 1 Department of Medicine, Discipline of Infectious Diseases, Laboratório de Virologia Clínica, Universidade Federal de São Paulo, Rua Pedro de Toledo, 781 - Vila Clementino, São Paulo, SP 04039-032, Brazil 2 Hospital São Paulo, Universidade Federal de São Paulo, São Paulo, Brazil Some studies have already demonstrated the broadspectrum antiviral potential of HCQ, a drug widely used as an antimalarial or in the treatment of autoimmune disease [7, 8]. Some studies have demonstrated the in vitro effectiveness of HCQ and chloroquine in controlling the replication of SARS-CoV-2 [9, 10]. Other observational study concluded hydroxychloroquine administration was not associated with either a greatly lowered or an increased risk of the composite end point of intubation or death. [11]. The UK RECOVERY trial also concluded that HCQ does not reduce the risk of dying in hospitalized patients [12]. Therefore, more studies need to be carried out to understand the real benefit of HCQ in the treatment of the..