A Case of Breakthrough COVID-19 during Hydroxychloroquine Maintenance.

There have been controversies on the prophylactic effect of hydroxychloroquine against severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2). We describe a patient, 60-year old Korean woman, with coronavirus disease 2019 (COVID-19) who had been taking hydroxychloroquine for 6 months. Her serum and saliva concentrations of hydroxychloroquine were 280 μg/L and 4,890 μg/L, respectively. The present case raises concerns on hydroxychloroquine's role as a prophylactic agent for COVID-19.