Pandemic Research Estimates 20,000 Hidden Infections in Hong Kong

The Faculty of Medicine launched a study of the pandemic last April with a focus on detecting unidentified local cases using serology tests. Results are now suggesting that there were at most about 20,000 hidden patients.

In hopes of understanding the overall situation in Hong Kong and epidemiological features of the infections, which will help evaluate and enhance infection control measures, the team recruited 4,198 individuals aged 18 or above between 21 April 2020 and 18 April 2021. Participants were asked to provide blood samples for a serology test for the Immunoglobulin G (IgG) antibodies, a sign of previous infection, and complete a questionnaire. Six or 0.14% of the participants were found to have the IgG antibodies. Having adjusted the figure using statistical methods, the team estimates that there were around 20,000 hidden patients in Hong Kong, which amounts to 0.3% of the city’s population.

According to Prof. Paul Chan (right), Chairman of the Department of Microbiology, the results reveal the ratio of confirmed cases to hidden ones in Hong Kong to be approximately 1 to 2, lower than that in other places. Geneva, for example, has a ratio of 1 to 11.6. Prof. Martin Wong (left) of the Jockey Club School of Public Health and Primary Care said it is possible for an infection to be asymptomatic and such hidden infections make it difficult for the authority to know exactly what the situation is. This study, he continues, will provide them with insights into the situation and help formulating control measures.