Information on questions commonly asked

Written by Saif Badran and Suhail A. Doi

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Covid-19 is such a threat because it can kill healthy adults in addition to elderly people with existing health problems and because it is transmitted efficiently with an infected person spreading the disease to two or three others (R0 about 2-3). Many people will shed the virus when only mildly ill or even when they are presymptomatic, meaning the asymptomatic phase of the disease. Such cases may be considered to have asymptomatic infection, but they usually, in the majority of cases, end up being presymptomatic on the date of identification/report but do go on to develop disease. The proportion of truly asymptomatic infections is unclear but appears to be relatively rare and does not appear to be a major driver of transmission in the ongoing pandemic for this reason. Most of such patients are identified through contact tracing and will have some clinical progression on follow-up. As an example, in a study of 23 patients who tested positive, 13 had asymptomatic infection of whom 10 patients developed symptoms seven days later. In another study of 24 asymptomatic patients identified through contact tracing, only 7 remained free of clinical abnormalities, were younger (median 14 y) and had clearance of virus within 2 – 15 days. The other 17 developed clinical or imaging evidence of disease.

The most common symptoms that presymptomatic subjects go on to develop are fever (almost everyone), fatigue and dry cough. However, fever might be very low grade