PIN51 Role of Asymptomatic Carriers in the Transmission of COVID-19: A Review

Abstract

There is limited data describing the role of asymptomatic carriers in the transmission of COVID-19. This review describes the characteristics of asymptomatic carriers, potentials for asymptomatic transmission and its implications on mitigation strategies. PubMed database was searched to identify studies conducted in humans and published in the English language. Snowball search was also conducted on Google Scholar and the reference list of selected studies was checked to identify additional studies. Articles published from the beginning of the COVID-19 pandemic in December 2019 to September 2020 were considered for inclusion. Three types of asymptomatic COVID-19 carriers were identified including pre-symptomatic cases, asymptomatic carriers with normal chest radiographs and asymptomatic carriers with abnormal chest radiographs. Pre-symptomatic cases are older and have abnormal chest radiograph and abnormal biochemical parameters including abnormal white blood cell and lymphocyte counts at the time of diagnosis compared to those who remain asymptomatic. Asymptomatic carriers with normal chest CT images constitute about one-third of all asymptomatic COVID-19 carriers. They are younger and have normal biochemical parameters at the time of diagnosis. Asymptomatic patients with abnormal chest radiograph represent about two-thirds of asymptomatic COVID-19 carriers. Limited data indicate that asymptomatic COVID-19 transmission is possible. Asymptomatic transmission has been reported among familial contacts of carriers. Asymptomatic transmission occur in both cases with normal and abnormal chest radiograph as well as those who have no obvious changes in biochemical parameters. Asymptomatic COVID-19 transmission varied in severity ranging from mild to severe infection. Evidence demonstrates that asymptomatic carriers contribute to the transmission of COVID-19 and have potential implications on community and healthcare transmissions including dialysis and long-term care facilities, as well as blood transfusion-related transmission. Mitigation measures should take into consideration the potential role of asymptomatic transmission.