COVID-19 spreads easily among people who live together
NEW YORK: COVID-19 spreads easily among people who live together and other family members, even before an infected person shows any symptoms, according to a modelling study that is the first-of-its-kind to quantify symptomless transmission. The research, published in The Lancet Infectious Diseases journal on Wednesday, also suggests the SARS-COV-2 that causes COVID-19 may spread more easily in households than severe acute respiratory syndrome (SARS) or Middle East respiratory syndrome (MERS). The analysis, based on contact tracing data from 349 people with COVID-19 and 1,964 of their close contacts in Guangzhou, China, found that people with COVID-19 were at least as infectious before they developed symptoms as during their actual illness.
The researchers, including those from the University of Florida in the US, also found that people aged 60 years or more were most susceptible to household infection with SARS-COV-2.
The study of people living together and family members -- not living at the same address -- and non-household contacts suggests that breaking the chain of transmission within households through timely tracing and quarantine of close contacts, in addition to case finding and isolation, could have a huge impact on reducing the number of COVID-19 cases. While the model has been updated to reflect the current knowledge about the transmission dynamics of COVID-19, the researchers caution that it is based on a series of assumptions, for example about the
length of incubation and how
long symptomatic cases are infectious, that are yet to be confirmed, and might affect the accuracy of the estimates. "Our analyses suggest that the infectiousness of individuals with COVID-19 before they have symptoms is high and could substantially increase the difficulty of curbing the ongoing pandemic," said Yang Yang from the University of Florida, who co-led the research. "Active case finding and isolation in conjunction with comprehensive contact tracing and quarantine will be key to preventing infected contacts from spreading the virus during their incubation periods, which will be crucial when easing lockdown restrictions on movement and mixing," Yang said. The researchers developed a transmission model that accounted for individuallevel exposure, tertiary transmission, potential exposure to untraced infection sources, and asymptomatic infections.
The study estimated the secondary attack rate -- the probability that an infected person transmits the disease to a susceptible individual -among people living together and family members, and nonhousehold contacts.