Hong Kong health authorities’ latest move to stop taking nasal swab samples for Covid-19 polymerase chain reaction (PCR) tests may allow more imported cases to enter the community, but does not pose a risk to the local pandemic situation, medical experts have said.
But respiratory medicine expert Dr Leung Chi-chiu on Monday said he found it “problematic” for the city’s government to opt for a less sensitive method when it had been spending a huge amount of resources on PCR testing.
The government earlier announced that from Tuesday, only throat swab samples would be collected for free PCR tests at government-run sites, including those at the airport, to boost the efficiency and capacity of the services.
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Leung, a former chairman of the Hong Kong Medical Association’s advisory committee on communicable diseases, said sensitivity could drop by one-third if only throat swabs were taken, but such a change might have “little effect” on the imported case situation.
Overseas studies had shown that the sensitivity of using both samples was 97 per cent, but that of throat swabs only reached 68 per cent, he added.
“But at this stage, we are not too concerned about imported cases. No matter how much the [tests’] sensitivity decreases, many cases can be detected at the airport,” he told a radio programme on Monday.
“Even if the imported cases enter the community, it will only lead to a small-scale transmission compared with transmission within the community. The proportion of imported cases among overall infections is still less than 10 per cent.”
The authorities on Saturday said a throat swab was one of the specimens recommended by the National Health Commission and commonly used in mainland China for PCR tests.
They added that the new arrangement had “reliable” sensitivity and could reduce the time for sample collection, as well as streamlining the collection procedure.
“The adjustment is conducive to enhancing the overall efficiency and boosting the capacity of testing services, while not affecting nucleic acid tests’ accuracy,” a government spokesman said, adding that self-paid tests were not subject to the changes.
But Leung said he could not understand why such changes were made.
“This is a bit problematic because the government is wasting a huge amount of resources [on PCR testing]. It also takes up much time for people to head to the testing stations, causing inconvenience,” he said.
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“If you are conducting PCR testing, but using a less sensitive method, it is contradictory to the initial intention of public health.”
Leung said the amount of PCR testing could be reduced as Hong Kong was on the road to normality, adding that initiatives should be focused on protecting high-risk groups or monitoring areas with an increased prospect of transmission when the healthcare system was under pressure.
He also suggested raising the threshold for compulsory testing, or replacing the PCR method with rapid antigen kits.
The Health Bureau revealed earlier that from November 2020 to August this year about 37.3 million PCR tests were conducted at community centres, mobile specimen collection stations and during “restriction-testing declaration” operations. As of April, HK$5.8 billion (US$738.8 million) had been spent on this, it said.
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Ricky Chiu Yin-to, an adjunct associate professor at Chinese University’s school of biomedical sciences who also operates a medical diagnostics start-up that runs a few testing centres, said while forgoing nasal swabs might increase the risks of having imported cases being leaked into the community, the subsequent mandatory medical surveillance of arrivals could also detect infections.
He said the new arrangement could reduce the sample collection time by two-thirds but the results would not be available any earlier.
He said although the new arrangement might slightly reduce the tests’ sensitivity, it was in line with the government’s goal to provide ample, high-quality, speedy, accessible and affordable services.
Currently, inbound travellers are required to undergo a PCR test on the first, third, fifth and seventh day of arrival as well as daily RAT tests.
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