New research has added to the growing body of evidence that asymptomatic patients suffering from Covid-19 are less likely to infect close contacts compared to severe cases. According to the study, published in the journal Annals of Internal Medicine, the risk for transmission of SARS-CoV-2 to close contacts of infected persons has not been well estimated.
"We wanted to evaluate the risk for transmission of SARS-CoV-2 to close contacts of persons infected with Covid-19 in Guangzhou region," said study researchers from Southern Medical University in China.
For the findings, the research team tracked more than 3,410 close contacts of 391 Covid-19 index cases between January and March 2020 to evaluate the risk for the disease transmission in different settings. They found that risk for secondary transmission of the novel coronavirus was less than four per cent among close contacts of persons with Covid-19.
In addition, secondary infections acquired while using public transportation were rare. In contrast, one in 10 household contacts was found to be infected.
The researchers also found that patients with more clinically severe disease were more likely to infect their close contacts than were less severe index cases. Those with asymptomatic cases were the least likely to infect their close contacts, the study said.
According to the team, the manifestation of certain symptoms, such as expectoration, in index cases, was also associated with an increased risk for infection in their close contacts.
"In conclusion, we found that the secondary attack rate of Covid-19 was relatively low, and household contacts were at higher risk of infection," the study authors wrote. "Moreover, patients with more clinically severe cases or those with symptoms were more likely to infect their close contacts," the team noted.