- Although people who don't show symptoms are 'very infective', there's probably not very many of them, respiratory disease expert Zhong Nanshan says
- But head of specialist Covid-19 team in Shanghai says asymptomatic carriers 'now pose the biggest risk' in terms of preventing imported cases
A Chinese doctor who spent time in Wuhan in January has tested positive for Covid-19 weeks after returning home to Henan province and despite spending 14 days in self-isolation, health authorities said on Sunday, raising concerns about the threat of asymptomatic carriers of the coronavirus.
Two of the doctor's colleagues in Henan, neither of whom had worked in Wuhan, also tested positive, officials said.
The news sparked alarm on social media.
"No symptoms is so horrible," a person said on Weibo, China's Twitter-like platform. "It's impossible to prevent it effectively. I hope the government can make the number of asymptomatic cases public."
As of Sunday, there had been more than 670,000 confirmed cases around the world and close to 32,000 deaths.
In China, which was the initial focus of the pandemic, the number of local infections has slowed almost to a halt, but the country continues to battle the threat of imported cases.
Zhong Nanshan, one of China's leading respiratory disease specialists, said in an interview with state broadcaster CGTN on Sunday that although asymptomatic virus carriers were "very infective because there is very high viral load in their upper respiratory tracts", he did not think there were many of them.
"Right now … the fatality rate is only 0.9 or 1 per cent," he said. "I suppose we don't have too many asymptomatic patients. If we did, they would be transmitting (the virus) to other people and pushing the number (of confirmed cases) higher.
"But now, it's actually going down, and in some provinces to close to zero. I don't think that's a big problem."
Meet the doctor who became an online celebrity for his straight talk
But not everyone is as optimistic as Zhong.
Speaking at a symposium in Shanghai on Friday, Zhang Wenhong, the head of the city's Covid-19 clinical expert team, said that asymptomatic carriers "now pose the biggest risk" among imported cases of infection, of which Shanghai had reported more than 100.
"Asymptomatic coronavirus carriers usually have strong immunity and show no symptoms for more than two weeks despite being infected," he said.
"If they return home from abroad and are not isolated in a timely fashion or are released too soon from their two-week quarantine, they pose a great risk of community infection."
Wang Xinhua, president of Guangzhou Medical University, said it was still too early to say what threat asymptomatic carriers posed.
"Confirmed cases with no symptoms do exist, but we don't know the specific number and the workings and characteristics of this (type of) carriage are not clear," he said.
"I think (in such people) the viral load is low and the virulence is weakened. If not, they would show symptoms."
What was important was for the government to focus its prevention and control measures in the right areas, Wang said.
"Anyone who has had close contact with an infected area or patient should be tested and isolated, but we don't have to test everyone. That's too much work and there is no need," he said.
"Tackling the asymptomatic and imported cases is the most important task."
Purchase the China AI Report 2020 brought to you by SCMP Research and enjoy a 20% discount (original price US$400). This 60-page all new intelligence report gives you first-hand insights and analysis into the latest industry developments and intelligence about China AI. Get exclusive access to our webinars for continuous learning, and interact with China AI executives in live Q&A. Offer valid until 31 March 2020.
Copyright (c) 2020. South China Morning Post Publishers Ltd. All rights reserved.