5 questions answered about asymptomatic COVID-19:
Screening for symptoms of COVID-19 and self-quarantine are good at preventing sick people from spreading the coronavirus. But more and more evidence is suggesting that people without symptoms are spreading the virus too. Monica Gandhi, an infectious diseases physician and researcher at the University of California, San Francisco, explains what is known about asymptomatic spread and why she thinks it may be a big part of what is driving the pandemic.
What does it mean to be asymptomatic?
SARS-CoV-2 – the virus that causes COVID-19 – can produce a range of clinical manifestations.
Some people who are infected never develop any symptoms at all. These patients are considered true asymptomatic cases.
When people do get sick from the coronavirus, it takes on average five days and as many as two weeks to develop symptoms that can range from very mild to extremely dangerous. The time between initial infection and the first symptoms is called the pre-symptomatic phase.
As an infectious disease physician, when I hear about asymptomatic spread of SARS-CoV-2, I think of a person who doesn’t have symptoms at the moment they give the virus to someone else. It doesn’t matter whether they are a true asymptomatic case or just pre-symptomatic; the public health risk is the same.
How many people are asymptomatic?
Estimates of the proportion of true asymptomatic cases – those who are infected and never develop symptoms – range from 18% to over 80%. The reasons for the huge range in estimates are still unclear, but some studies are better than others.
The most accurate way to determine the rate of asymptomatic cases is to test people regardless of whether or not they have symptoms – an approach called universal mass testing – and track them over time to see if they develop symptoms later. A recent mass testing campaign in San Francisco found that 53% of infected patients were asymptomatic when first tested and 42% stayed asymptomatic over the next two weeks.
Go to link