Hong Kong’s policy of subjecting entire residential blocks to Covid-19 testing uncovered just 46 infections for every 100 buildings targeted during the early weeks of the fifth wave, researchers at the University of Hong Kong have found, calling the long-standing practice inefficient and not cost-effective.

The team, which included professors Benjamin Cowling and Gabriel Leung, argued that while building-wide testing had worked well in the earlier stages of the pandemic, it was now past its use-by date and resources should be diverted elsewhere.

“Compulsory testing notices can be an essential method when attempting to maintain local elimination – ‘zero covid’ – and most impactful early in an epidemic when the benefit remains of stemming a new wave,” the academics wrote in a pre-print study posted earlier this week that is yet to be peer-reviewed.

Residents in Sheung Shui undergo Covid-19 testing in March.

Lockdowns were initially ordered whenever a single infection was found in a building, an exercise known as restriction testing declarations, which exasperated residents.

But health authorities later eased the policy so that testing was triggered by a combination of factors, including viral loads in sewage samples. Residents were also allowed to complete the screening by taking polymerase chain reaction (PCR) tests in community centres within a set number of days.

That approach had yielded only marginal gains in controlling infections, the university team argued.

“However, residential [compulsory testing notices] and [restriction testing declarations] appear to be an expensive method of finding small numbers of infections during periods of sustained community transmission, [and] therefore only make at most a limited contribution to mitigating local spread of infection,” they said.

The team analysed testing orders, including those accompanied by an overnight lockdown, from the start of the pandemic in 2020 to February 15 this year, when the fifth wave driven by Omicron was in its sixth week.

They estimated that for every 100 buildings tested, each with hundreds of residents involved, 29 infections on average were uncovered during the first four waves, and 46 in the fifth one.

That translated to just one reported case in 55.2 per cent of the residential buildings targeted. About 13 per cent of daily reported cases were identified through a mix of these compulsory testing notices.

The academics noted that infections spreading via large vertical or horizontal spaces in residential blocks remained limited, with Omicron estimated to typically spread between two to eight flats.

They cited previous studies that showed 0.1 per cent of total local cases were due to vertical transmission in tall buildings during the first four waves, with the figure rising to 0.9 by the end of the Omicron-fuelled fifth wave.

On September 26, the Health Bureau announced that it was “gradually reducing” the number of overnight lockdown screenings, citing “recent epidemic developments”.

But orders that only required residents to complete the testing at community centres were still issued regularly and carried a hefty fine of HK$10,000 for non-compliance.

According to calculations by the Post, law enforcement officers have carried out one or two operations a day in the last week, and handed out the HK$10,000 penalty to 31 residents.

Cowling told the Post he believed money could be better spent elsewhere.

“I think there is no need to spend such a large amount of money each day to find 13 per cent of the daily Covid-19 cases. Most of the Covid-19 cases found will no longer be contagious, because people with Covid-19 are only contagious for a short time but can test positive by PCR tests for weeks after infection,” he said.

“The money currently being used to pay for compulsory testing could be redirected to other more cost-effective uses in public health.”

If the government failed to get right the “dynamic ratio” of the costs and benefits of pandemic curbs, public trust in authorities could erode, the academics warned.

The Health Bureau told the Post that compulsory testing was part of a coherent strategy to tackle cases, along with encouraging voluntary testing to identify infections early and cut transmission chains.

From October 1 to 13, the daily number of cases detected through compulsory testing notices and voluntary testing ranged from more than 900 cases to nearly 1 400, representing a positive rate of between 0.8 and 1.28 per cent, a spokeswoman said.

“If the current compulsory testing notice arrangement and a sound testing infrastructure were not in place to help identify infected persons at an early stage, local transmission could have been even worse,” she said.

“In this regard, there is a need to maintain the anti-epidemic policy of ‘compulsory testing on a mandatory basis, targeted testing on an obligatory basis and testing on a voluntary basis’. This will also help lower the occurrence of severe cases, thus alleviating the pressure on public healthcare system.”