Coronavirus: China hid 'silent carriers' who make up a third of the cases in official count, claims report
China's official count of confirmed cases does not include more than 43,000 "silent carriers" of COVID-19: individuals with delayed or no symptoms.
According to confidential documents accessed by the South China Morning Post (SCMP), China has not disclosed that it quarantined and monitored these silent carriers, who make up a third of the cases. This could, in turn, complicate the strategies being used by countries -- who are taking lessons from China -- to control the virus, says SCMP.
China has confirmed more than 81,000 cases and 3,270 have died so far.
The official numbers may not represent the scale of the outbreak
According to the World Health Organization (WHO), people who test positive for the virus are considered confirmed cases, regardless of whether they show symptoms or not. South Korea and Singapore have stayed true to this: they aggressively tested people with contacts with confirmed cases. South Korea found that more than 20% of their patients displayed no symptoms or were asymptomatic until they were discharged.
“Korea currently has a significantly higher rate of asymptomatic cases than other countries, perhaps due to our extensive testing,” Jeong Eun-kyeong, director of South Korea’s CDC, told a press briefing on March 16.
Though China did the same, their official tally excluded people without symptoms, even if they tested positive. China categorized them as ‘positive cases’ instead of ‘confirmed cases'.
Other countries, including the US and Britain, may not know the scale of the outbreak because they are only testing people with symptoms of COVID-19.
We do not know the proportion of mild or asymptomatic cases
Scientists do not yet understand the role people with no or mild symptoms play in driving the virus' spread. Earlier, the World Health Organization (WHO) said that the proportion of people showing no symptoms was unclear. It "appears to be relatively rare and does not appear to be a major driver of transmission", they wrote in their report.
But a recent study predicted that 86% of these individuals, who were undiagnosed, may have helped fuel the outbreak that took hold in China.
"The explosion of COVID-19 cases in China was largely driven by individuals with mild, limited, or no symptoms who went undetected," says co-author Dr Jeffrey Shaman, professor of environmental health sciences at Columbia University Mailman School. Two-thirds of the confirmed cases may have contracted the infection from the undetected group, the study adds.
“Understanding the proportion of asymptomatic or mildly ill cases is just going to be important for us to understand what is driving this particular epidemic,” Michael Osterholm, director of the University of Minnesota’s Center for Infectious Diseases Research and Policy in Minneapolis, told Nature.