According to classified Chinese government statistics seen by the South China Morning Post, as many as one third of those who test positive for COVID-19 are “silent carriers”. At the end of February, China quarantined 43,000 people who had tested positive for the deadly virus, but who showed no outward signs of infection. The number was not included in official figures, which at the time stood at 80,000.
The discovery has huge implications for the strategies employed by countries in their fight to contain the pandemic.
Increasingly, scientists believe that those showing no symptoms of the disease are still capable of transmitting the virus to others.
This challenges the conclusion of a report published by the World Health Organisation, after a team of its experts had visited China.
The report estimated that asymptomatic infections accounted for only one to three percent of cases.
However, a Japanese epidemiologist put the proportion of asymptomatic Japanese patients evacuated from Wuhan at 30.8 percent, a figure similar to the classified Chinese government data.
Hiroshi Nishiura from Hokkaido University along with a group of experts wrote a letter in February to the International Journal of Infectious Diseases.
Mr Nishiura said: “The number of novel coronavirus (Covid-19) cases worldwide continues to grow, and the gap between reports from China and statistical estimates of incidence based on cases diagnosed outside China indicates that a substantial number of cases are underdiagnosed.”
He added: “The asymptomatic ratio … could be higher among children than in older adults.
He added: “There are many reports of transmission around one to two days before symptom onset.”
These new findings have led to increasing calls for Western Governments to follow China and South Korea’s example of testing everyone known to have come in contact with coronavirus sufferers.
Currently, the US, the UK and Italy do not test people without symptoms.
Moreover, America and European countries are only testing airport arrivals if they show symptoms of COVID-19.
In contrast, Hong Kong, which has successfully been able to contain the virus, tests all arrivals .
It comes as a US diagnostics company has developed a new molecular based test, that will allow for quick diagnosis of the coronavirus.
The new test has been developed by the molecular diagnostics company Cepheid and should be rolled out by the beginning of this week.
It will allow hospitals and clinics to carry out tests and confirm diagnosis of infection on-site , without the need to send samples to a dedicated diagnostics laboratory.
The molecular based test allows for a high degree of accuracy and uses the company’s GeneXpert machine to produce results on-site.