Undetected cases, many of which were likely not severely symptomatic, were largely responsible for the rapid geographic spread of the COVID-19 outbreak in China, according to a new study.
This scanning electron microscope image shows SARS-CoV-2 (round magenta objects) emerging from the surface of cells cultured in the lab. The virus shown was isolated from a patient in the U.S. Image credit: NIAID-RML.
“The explosion of COVID-19 cases in China was largely driven by individuals with mild, limited, or no symptoms who went undetected,” said Professor Jeffrey Shaman, a researcher at the Columbia University Mailman School.
“Depending on their contagiousness and numbers, undetected cases can expose a far greater portion of the population to virus than would otherwise occur.”
“We find for COVID-19 in China these undetected infected individuals are numerous and contagious.”
“These stealth transmissions will continue to present a major challenge to the containment of this outbreak going forward.”
In the study, Professor Shaman and colleagues used a computer model that draws on observations of reported infection and spread within China in conjunction with mobility data from January 10-23 and January 24-February 8.
They found that 86% of all infections were undocumented prior to January 23, 2020 travel restrictions.
Per person, the transmission rate of undocumented infections was 55% of documented infections (46-62%), yet, due to their greater numbers, undocumented infections were the infection source for 79% of documented cases.
Government control efforts and population awareness have reduced the rate of spread of the SARS-CoV-2 virus in China. After travel restrictions and control measures were imposed, it spread less quickly.
The scientists caution that major changes to care-seeking or patient documentation practices, as well as rapid developments with regard to travel restrictions and control measures, may make predictions difficult.
“Heightened awareness of the outbreak, increased use of personal protective measures, and travel restriction have helped reduce the overall force of infection; however, it is unclear whether this reduction will be sufficient to fully stem the virus spread,” Professor Shaman said.
“If the novel coronavirus follows the pattern of 2009 H1N1 pandemic influenza, it will also spread globally and become a fifth endemic coronavirus within the human population.”
The study was published in the journal Science.
_____
Ruiyun Li et al. Substantial undocumented infection facilitates the rapid dissemination of novel coronavirus (SARS-CoV2). Science, published online March 16, 2020; doi: 10.1126/science.abb3221
This article is based on text provided by Columbia University.
