The researchers aimed to understand how the RT-PCR cycle threshold (Ct) value for SARS-CoV-2, a semiquantitative measure of viral RNA, relates to cultivable virus, a proxy for infectiousness. A total of 754 upper respiratory tract samples from 425 symptomatic cases that tested positive for SARS-CoV-2 with a clear record of dates of symptom onset and sample collection were used. Results indicate that viral RNA peaked at symptom onset and steadily decreased the following 10 days. Cultivable virus was detected from 41% of samples. There were no differences in Ct values between people with asymptomatic, mild-to-moderate, or severe illness, but the detection of cultivable virus peaked around time of symptom onset. With each unit increase in Ct value, the odds ratio of recovering infectious virus decrease by 0.67. This study is one of the first reports of cultivable virus from completely asymptomatic individuals. Infection control measures should be implemented for persons with mild-to-moderate COVID-19 focused immediately after onset of symptoms. The significance of low titres of infectious virus is uncertain due to the unknown human infectious dose.