How Asymptomatic Cases Fuelled Spread

As India nears the 20,000 cases mark, a senior scientist at Indian Council of Medical Research said as much as 80% of all cases could be asymptomatic — infected people not showing any signs of illness. But what is an asymptomatic case and what causes it?

Pre-Symptomatic Or Asymptomatic?

WHO notes it may more often be a case of people being “presymptomatic” than completely asymptomatic. ProPublica reported WHO found few cases where “a patient tests positive and has zero symptoms for the entire course”. People who are pre-symptomatic show no symptoms when they test positive but develop symptoms later. A WHO team in China found about 75% of people who were early on classified as “asymptomatic” went on to develop symptoms while a study in the Science journal said 86% of all infections in China were “undocumented” prior to its lockdown.

Why Some People Could Be Asymptomatic

Robert Redfield, director of the US Centers for Disease Control and Prevention, said as many as 25% of people may be asymptomatic, while other estimates range from 18% to 30%. It is still unclear why some people exhibit symptoms while others don’t. Two theories suggest it could be linked to an individual’s stronger innate immune response to the virus or if they are exposed to a smaller viral load. Neither theory has been proved yet.

Only Testing Can Give A True Picture

Since there is asymptomatic spread and there may be people who don’t show serious enough symptoms and yet spread the disease, it is clear why testing is such a crucial factor in controlling the disease. In fact, ProPublica quotes a health expert as saying that “symptomatic versus asymptomatic isn’t really the appropriate dividing line” and that it should be “documented versus undocumented infection”, that is those confirmed and those not.

People May Be Most Infectious In Earliest Phase

How infectious a person is depends on what experts describe as the viral load of the disease carried by them. For Covid-19, studies have found that the viral load is the highest right at the onset of the disease. The combination of pre-symptomatic transmission and peak viral load at outset for Covid-19 “could account for the fastspreading nature of this epidemic”, said authors of a Lancet study.

How Are They Spreading Covid-19?

When doctors say this disease spreads primarily via respiratory droplets they don’t mean only those released while coughing or sneezing. Because we can be releasing droplets while speaking, breaking into a laugh, singing, etc. In a closed space, there is a real risk that those droplets may hang in the air long enough to infect others. Hence, the need for all to wear masks and constantly wash their hands, because one may contract the virus from touching an infected surface and then touching one’s nose or mouth.

Source: ProPublica, Inverse, media reports