Early, large-scale studies using mathematical modelling of outbreaks in Tianjin, China, and Singapore in January and February have also found significant amounts of spread by people who had not yet developed symptoms.
Both studies were posted on MedRxiv, a pre-print server founded by Yale University, the medical journal BMJ and Cold Spring Harbor Laboratory in New York. Articles on this server have not been reviewed by the authors' scientific peers.
A study posted Sunday by Belgian and Dutch researchers shows that between 48% and 66% of the 91 people in the Singapore cluster contracted the infection from someone who was pre-symptomatic. Of the 135 people in the Tianjin cluster, between 62% and 77% caught it from someone was pre-symptomatic.
Canadian, Dutch and Singaporean researchers looked at the same outbreaks in Tianjin and Singapore and found that infection was transmitted on average 2.55 days and 2.89 days before symptom onset respectively in each location.
"Our analysis would suggest that presymptomatic transmission is pretty commonplace," said the study's lead author, Caroline Colijn, who leads the mathematics, genomics and prediction in infection and evolution research group at Simon Fraser University in British Columbia.