Coronavirus: Hong Kong scientists to identify city’s ‘invisible’ Covid-19 carriers
- Chinese University study of asymptomatic virus carriers to determine extent of their role in local spread of Covid-19
- Microbiologists want to find out why some of those infected do not develop symptoms, with findings to inform government policy
Chinese University scientists are aiming to identify the number of asymptomatic virus carriers in Hong Kong and bolster the city’s fight against Covid-19.
Past studies have revealed those infected might exhibit only mild symptoms, or even none at all.
Professor Paul Chan Kay-sheung, chairman of Chinese University's department of microbiology, said his team wanted to find out more about why some of the infected were “invisible”.
“Was it because of their age such that they were asymptomatic? Or was it because of their jobs that rendered them a higher risk of infection?”
In Hong Kong, some arriving in the city on flights, or close contacts of asymptomatic patients, were only found to be infected after screening at the airport or when tested by the health authority.
As of Wednesday, Hong Kong has 1,037 confirmed coronavirus cases after reporting four consecutive days of no new infections.
But health authorities said earlier that the source of infection for some cases could not be traced.
Chan, who leads the study, said it would reveal the proportion of invisible patients in the community, while helping them understand more about the role, if any, of asymptomatic carriers in the local spread of the disease.
He said the antibody Immunoglobulin G (IgG) would be tested in subjects’ blood and saliva samples.
The antibody is usually found in patients about two to three weeks from the onset of infection, he said, which could remain in the bloodstream for years or even longer.
But the study would not target any confirmed Covid-19 patients, he said, adding only those without respiratory or other relevant symptoms, and who had mostly stayed in Hong Kong over the past six months, would be eligible to take part.
“[Those] who may suspect they have been infected a few months ago, they may be interested to join our study,” Chan said, adding medical workers could also participate in the programme.
The study is due to start this week and is expected to return its findings within a year.
The recruitment of participants over two weeks begins on Wednesday, while testing is set to take place between May and August.
Chinese University medical faculty professor Martin Wong Chi-sang said the 3,000 individuals would be selected through a randomised process with the help of computer programmes, to ensure they were relatively representative of the Hong Kong population.
“For example, we might probably take half of the participants as male and the other half female. And we also consider their age groups and geographical location,” Wong said.
Chan added that in Europe the proportion of invisible patients ranged from about 2 to 30 per cent of the population, while an earlier Post analysis this month found that 18 per cent of the roughly 1,000 infected Covid-19 cases were asymptomatic.
But he believed the proportion of those in Hong Kong would not be at a very high level.
“Our hypothesis was that if Hong Kong’s proportion of invisible patients was at about 1.5 per cent, it would take a study of [at least] 3,000 people to find out. It would be better if we could expand our sample base … but we also had to balance with its cost-effectiveness,” he said.
The findings of the study will be submitted to the Hong Kong government to help them formulate infection control measures and policies.
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