Prolonged SARS-CoV-2 cell culture replication in respiratory samples from patients with severe COVID-19

Abstract

\n Objectives\n This study compares the infectivity of SARS-CoV-2 in respiratory samples from patients with mild COVID-19 with those from hospitalised patients with severe bilateral pneumonia. In severe COVID-19, we also analysed the presence of neutralising activity in paired sera.\n \n Methods\n We performed cell cultures on 193 real-time reverse transcription polymerase chain reaction respiratory samples, positive for SARS-CoV-2, obtained from 189 patients at various times, from clinical diagnosis to follow-up. Eleven samples were obtained from asymptomatic individuals, 91 samples from 91 outpatients with mild forms of COVID-19, and 91 samples from 87 inpatients with severe pneumonia. In these patients, neutralising activity was analysed in 30 paired sera collected after symptom onset >10\xa0days.\n \n Results\n We detected a cytopathic effect (CPE) in 91 (91/193, 47%) samples. Viral viability was maintained for up to 10\xa0days in the patients with mild COVID-19. In the patients with severe COVID-19, the virus remained viable for up to 32\xa0days after the onset of symptoms. Patients with severe COVID-19 presented infectious virus at a significantly higher rate in the samples with moderate to low viral load (cycle threshold value >26): 32/75 (43%) versus 14/63 (22%) for mild cases (P < 0.01). We observed a positive CPE despite the presence of clear neutralising activity (NT50 >1:1024 in 10% (3/30) of samples.\n \n Conclusions\n Patients with severe COVID-19 might shed viable virus during prolonged periods of up to 4\xa0weeks after symptom onset, even when presenting high cycle threshold values in their respiratory samples and despite having developed high neutralising antibody titres.\n