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Coronavirus Hong Kong
OpinionComment
Daniel Z. Long
Daniel Z. Long

Opinion | Coronavirus third wave: Group testing can address Hong Kong’s limited capacity

  • Hong Kong currently has a quarter to a fifth of the capacity it needs to handle Covid-19, and testing the entire population is prohibitively expensive
  • Emulating the group testing approach taken in Germany, Israel and the mainland can help make more efficient use of the city’s resources

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Two people are tested at the windows of a testing vehicle in Beijing on June 30. The success of group testing methods in containing Covid-19 outbreaks in Wuhan and Beijing suggest it might be a useful approach for Hong Kong given the city’s constrained testing capacity. Photo: Reuters
Daniel Z. Long

One of the most important concerns in mitigating the Covid-19 pandemic is testing. In Hong Kong, the issue of insufficient capacity for testing has often been raised. For example, Professor Lo Chung-mau at the University of Hong Kong recently suggested the city needs to increase its testing capacity to 20,000 tests daily. 

Hong Kong can only support 4,000 to 5,000 tests per day at present. Additional resources, such as testing facilities, must be allocated to increase the testing capacity. However, from the perspective of decision science, we can use the same amount of resources more efficiently through group testing.

Group testing was first proposed in 1943 by Robert Dorfman, an economist at Harvard University, to identify the presence of syphilis in the US Army. Like the current Covid-19 pandemic, it was expensive to test every soldier for syphilis. Dorfman proposed group testing as follows: samples from groups are first tested, and if a group tests negative, all individuals in the group are declared to be negative. Otherwise, every individual in the group is tested separately.

For example, consider a case in which one out of 100 subjects is positive. By dividing the 100 subjects into five groups of equal size, group testing only requires 25 tests: one test for each of the five groups and 20 separate tests for the 20 subjects in the group returning a positive test. By contrast, testing all subjects separately requires 100 tests.

In practice, group testing has been adopted on the mainland to contain the spread of Covid-19. Wuhan tested its entire population of 11 million people in May using group testing. Groups of five to 10 samples were tested, and they tested individuals only if a group was positive. As most groups proved negative – no positive test was reported in 97 per cent of communities – the method sped up the procedure significantly and saved test kits.

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Beijing has also done mass testing. After the outbreak near the Xinfadi wholesale food centre, the city expanded its daily testing capacity to 230,000, and a five-sample grouping allowed about 1 million people to be tested. Finally, Beijing conducted tests on all residents in medium- and high-risk areas.
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