The detection and spread of an emerging respiratory pathogen are accompanied by uncertainty over the key epidemiological and serologic characteristics of the novel pathogen and particularly its ability to spread in the human population and its virulence (case-severity). This is the case for the COVID-19 virus, first detected in Wuhan city, China in December 2019 (1).
To date initial surveillance has focused primarily on patients with severe disease, and, as such, the full spectrum of the disease, including the extent and fraction of mild or asymptomatic infections that do not require medical attention are not clear. Estimates of the case fatality ratio, and other epidemiological parameters, will likely be lower than current crude mortality estimates once the full spectrum of disease is able to be included in the denominator. In addition, the role of asymptomatic or subclinical infections in human-to-human transmission of COVID-19 virus is not well understood and it is not yet clear whether those who are reported as asymptomatic may be able to transmit the virus to other individuals.
With a novel coronavirus, initial seroprevalence in the population is assumed to be negligible due to the virus being novel in origin. Therefore, surveillance of antibody seropositivity in a population can allow inferences to be made about the extent of infection and about the cumulative incidence of infection in the population.