Lack of sensitivity for switching throat swab for free nucleic acid tests, say experts

Experts were bewildered by the government's decision to collect only the throat swab samples for free nucleic acid tests starting Tuesday, replacing the current practice of collecting nasal and throat swab samples.

The government announced last week that throat swab samples would be collected for free nucleic acid tests conducted at community testing centres and stations, ad-hoc specimen collection stations, and inbound testing stations at the airport starting tomorrow.

Respiratory expert Leung Chi-chiu said that the sensitivity of the throat swab samples is relatively low, and he had no idea why the government would decide to make such changes at this stage.

He pointed out that the accuracy rate of using both throat and nasal swab samples can reach up to 97 percent, while collecting only the throat swab samples will see the sensitivity decline to 68%.

Ricky Chiu Yin-to, adjunct associate professor at the School of Biomedical Science at the Chinese University of Hong Kong, expressed that while the sensitivity will suffer a hit, collecting only the throat swab samples can speed up the whole testing process.

Chiu said collecting samples from the throat area is a viable alternative, as the virus are most concentrated in the throat at first for patients infected with Omicron, making it the best way to seek out cases that are still in the early stages.

But he emphasizes that collecting both throat and nasal samples is the ideal method when coming to test cases where the virus count is relatively low.