“Before the programme, we had been recording a downward trend of [the] number of cases reported through both the PCR [polymerase chain reaction] test and the RAT platform,” Chuang said. “I think all the pointers in the community [and] the surveillance indicate that there is a lower rate of infection at the present moment.”

Chuang was referring to the surveillance programme carried out by the University of Hong Kong, which recruited 10,000 residents citywide to conduct daily rapid tests to project the number of infections in the overall population.

According to the latest projection, an estimated 0.2 per cent of the city’s 7.4 million population were infected on Monday.

Chuang said a sewage study conducted by authorities and PCR detection also showed low infection rates.

The voluntary mass rapid test screening only required participants to declare their positive results, and it is uncertain how many had heeded the government’s call to join the exercise and how many had tested negative.

Asked how many of the reported cases came from voluntary participants of the mass screening, Chuang gave an estimate of about 800, as authorities gauged that half of the 1,696 RAT positive cases recorded on April 8, the first day of the three-day exercise, were picked up after people were encouraged to take part.

“We assume that in the recent few days, the number of PCR tests reported [was] similar to the number of rapid antigen tests reported,” Chuang said. “I think half of the cases detected … were additional cases through this programme because the numbers recorded [on the first day] did not follow the usual trend.”

A total of 774 and 658 cases were reported on the second and the third days respectively, similar to the number of infections detected by PCR tests.

Hong Kong recorded 1,433 new Covid-19 cases on Tuesday. Another 59 deaths were also reported, including seven backlogged ones, bringing the overall tally of Covid-related fatalities to 8,886 since the pandemic began.

The city’s overall tally of confirmed cases stands at 1,193,023.

Ricky Chiu Yin-to, an adjunct associate professor at Chinese University’s school of biomedical sciences and the CEO of a major supplier of rapid antigen tests (RAT), said on Tuesday that the number of infections detected during the three-day at-home screening drive was lower than he had expected.

“I expected it to be four digits, or over 10,000,” he said on a radio show, offering two possible explanations for the lower figure.

One, he said, was that the fifth wave of infections was easing, “and there are fewer invisible chains of transmission” in the community. However, he added, “I think it is more likely that the proportion of people who took part in the exercise was not large enough.”

Still, he said the overall effectiveness of the voluntary mass testing was “satisfactory”, as 65 per cent of the cases uncovered had been asymptomatic.

“They tested positive with the RAT, which means their viral load was high, which might have led to community transmissions … so it is nice that these cases were detected,” he said.

Chiu suggested authorities conduct a poll or telephone survey to attempt to gauge the level of participation in the drive, or require the public to also upload their negative results to the government platform.

“The biggest flaw of the testing was that the total number of participants was unknown, so we cannot see the full picture of the pandemic,” he said.

“With the low population coverage and selection bias [of the voluntary screening], l do not think it adds much to other current indicators from sewage testing, mandatory testing positive rates or the University of Hong Kong’s modelling study,” respiratory expert Dr Leung Chi-chiu said.

Residents should consider PCR testing on top of using RAT kits to avoid overdiagnosis, he said.

Meanwhile, the Hospital Authority’s chief manager Larry Lee Lap-yip said visiting restrictions for dying and critically ill Covid-19 patients would be relaxed, with visitors required to test negative using an RAT kit within 24 hours before coming to hospital.

People with proof of infection or recovery from Covid-19 were waived from the requirement for three months, he added, but all visitors had to undergo a seven-day medical surveillance following the visit.

Visiting arrangements in all public hospitals were suspended in early January after they were swamped with Covid-19 patients.

“During the pandemic, visiting arrangements are somewhat limited, but hospitals will try their best to arrange for compassionate visits,” he said, adding that online interactions could be arranged for other patients.

The government announced on Monday that students would be required to undergo daily rapid antigen testing when in-person classes resumed on April 19. Only students with negative test results would be allowed to enter schools.

Chiu said parents should not let their children use the test kits themselves, as they might hurt themselves when inserting the swab or fail to take adequate samples.

“Parents should insert the swab slowly and stop when they sense resistance in the nostrils,” he said.

Undersecretary for Education Christine Choi Yuk-lin said on Tuesday that schools would have to report any infections among students and staff to the Department of Health before 10am every day. However, they could choose their own methods of keeping a record of the results, such as asking students to jot it down on their handbooks or submit a photo of the test.

She added that if students who forgot to do a test arrived at school, they would be barred from classes.

“The school will have to call the parents and ask them to take the children home. [Or] if parents agree, the children can do a test at school,” she told a radio show.

Meanwhile, rail operator MTR Corporation will begin increasing train services in phases from April 15, after having cut back for lack of demand, in preparation for the influx of students commuting.

In an announcement on Tuesday, the MTR said about 5,200 train trips a week would be added across nine railway lines. To facilitate travel for university entrance exam candidates between April 22 and May 14, additional trips will also run at around 6am and 7am on test days.

“Heavy rail service during peak hours and most of the non-peak hours will return to the level before the outbreak of the fifth wave of the pandemic in January 2022,” the company said.

Separately, three hotels originally set aside as community isolation centres for Covid-19 patients with mild symptoms or are asymptomatic will be repurposed as designated quarantine facilities from April 14. The Cordis in Mong Kok, Royal Pacific Hotel and The Kowloon in Tsim Sha Tsui will provide an additional 2,000 rooms.

From May 1, four hotels originally for foreign domestic helpers will also be made available for other Hong Kong residents returning to the city. Reservations start on April 19 for Courtyard by Marriott in Sha Tin, iclub Ma Tau Wai Hotel, O’Hotel and Rambler Garden Hotel.

Domestic helpers who have already made reservations for these four hotels will not be affected.