I congratulate Ai et al. for their efforts in analysing a large cohort of corona virus disease 2019 (COVID-19) patients (1). Their results and insights will be helpful for the future in case similar scenario would occur again. However, we need also to re-emphasise the background where and when their data were collected. Their patient data were based in a tertiary hospital in Wuhan and during the period of Jan 6, 2020 to Feb 6, 2020. During this period in Wuhan the attention was mainly paid to the patients with more severe symptoms. While the clinical severity of the patients was not provided in Ai et al.’s paper, it is highly probable that a large proportion of their patients had moderate to severe grades severity.
The results from hospital-based patients usually do not represent the patients in general population, where the proportion of asymptomatic virus carrier and milder cases will be much larger. Patients during their latency period will also be CT negative but contagious. COVID-19 does not necessarily have pneumonia, thus the once-used-name of novel coronavirus pneumonia has been replaced with COVID-19. For milder cases, the chest CT positive rate will be much lower (2), and chest CT positive rate among asymptomatic COVID-19 patients remain unknown. For these cases, the role of biological pathogen testing can be more important.