MUMBAI: One in 10 patients of the new pandemic viral fever, Covid-19, gets infected by a patient who exhibits no symptoms at all, estimates a new study.While it is easy to quarantine or isolate a patient with obvious symptoms of Covid-19 such as fever, cold and sniffling, it is the asymptomatic patient — the individual free of symptoms despite carrying the virus — who is emerging as a big worry for health officials across the world.The new estimate, worked out by infectious diseases specialists of the University of Texas at Austin, could help health officials draw up better surveillance plans. The Texan team found that time between cases in a chain of transmission is less than a week. Germany was the first country to suffer due to an asymptomatic Chinese official who transmitted the coronavirus to a German businessman, who suffered a 24-hour fever and infected two of his workers.The luxury cruise-liner Diamond Princess is another case in point: of the 634 confirmed cases of the coronavirus, more than half (328) were asymptomatic.Not surprisingly, the US Centers for Disease Control and Prevention recommends that contacts of asymptomatic cases too should selfisolate for 14 days.The Texan paper, which will soon be published in the ‘Emerging Infectious Diseases’ journal, is the joint effort of scientists from the US, France , China and Hong Kong to calculate the “serial interval” of the virus.“To measure serial interval, the scientists look at the time it takes for symptoms to appear in two people with the virus: the person who infects another, and the infected second person,” said the paper, claiming to be the first study to estimate the rate of asymptomatic transmission.The researchers found the average serial interval for the novel coronavirus in China was approximately four days.The team looked at 450 infection case reports from 93 cities in China and found the strongest evidence yet that people without symptoms must be transmitting the virus, known as pre-symptomatic transmission. “More than 1 in 10 infections were from people who had the virus but did not yet feel sick,” the paper concluded.