Exclusive | A third of coronavirus cases may be ‘silent carriers’, classified Chinese data suggests
- More than 43,000 people in China had tested positive without immediate symptoms by the end of February and were quarantined
- It is still unclear what role asymptomatic transmission is playing in the global pandemic
More than 43,000 people in China had tested positive for Covid-19 by the end of February but had no immediate symptoms, a condition typically known as asymptomatic, according to the data. They were placed in quarantine and monitored but were not included in the official tally of confirmed cases, which stood at about 80,000 at the time.
Scientists have been unable to agree on what role asymptomatic transmission plays in spreading the disease. A patient usually develops symptoms in five days, though the incubation period can be as long as three weeks in some rare cases.
One obstacle is that countries tally their confirmed cases differently.
The World Health Organisation classifies all people who test positive as confirmed cases regardless of whether they experience any symptoms. South Korea also does this. But the Chinese government changed its classification guidelines on February 7, counting only those patients with symptoms as confirmed cases. The United States, Britain and Italy simply do not test people without symptoms, apart from medical workers who have prolonged exposure to the virus.