Investigation of nasopharyngeal viral load at discharge in patients with COVID-19

This study aimed to assess the nasopharyngeal viral load at discharge or time of discontinued isolation in coronavirus 2019 (COVID-19) patients admitted to our hospital and discharged under the current symptom-based criteria in Japan. Patients diagnosed with COVID-19 by reverse transcription polymerase chain reaction and hospitalized at Toyama University Hospital were included in the analysis. Nasopharyngeal viral load was measured when symptom-based criteria for discharge or end of isolation in the accommodations were met, and examined the relationship between viral load and days after onset or age. From the perspective of virus isolation limit, the amount of infectious viral load was defined at 50 copies/μL by nasopharyngeal sample. Thirty-three patients with laboratory-confirmed COVID-19 were included in the analysis, after excluding critical and fatal cases. Mean nasopharyngeal viral load at discharge or end of isolation was 1.90 log-copies/μL, and 64% of patients were discharged with over 50 copies/μL. No correlation was apparent between age and viral load at discharge, and viral load remained relatively high at discharge or end of isolation in all age groups. Although attempts at infectious virus isolation are necessary, infection control precautions even after discharge or discontinued isolation in accommodations may be needed, as the date of onset mostly depended on self-reporting by patients.