A medical worker works at a nucleic acid testing lab in Xi'an, Shaanxi Province on December 26, 2021. Photo: VCG

Xi'an, capital of Northwest China's Shaanxi Province and home to about 13 million people, is set to launch another round of city-wide nucleic acid testing on Monday.  

In order to enhance the accuracy of the testing, Xi'an authorities announced they will further strengthen anti-epidemic measures starting at 12:00 am on Monday, requiring all city residents to stay at home with the exception of going out for a nucleic acid test, according to media reports.    

Xi'an has carried out three rounds of citywide nucleic acid testing since December 21.  

At a press conference on Saturday, local officials explained that they carried out rounds of testing in order to enhance accuracy.

The recovery of some infected patients is intermittent. So, if an infected person is shedding virus when going to take a nucleic acid test, or the virus concentration is below the lowest testing limit, they would not be detected, especially for asymptomatic virus carriers at early stages of the infection, according to the health officials.  

The depth of insertion of the swab, the position of the head while collecting a sample , how long the swab is in contact with the throat and how medical staff administer the test all could affect the accuracy of the results and lead to infections being missed, the officials noted. 

The large population of Xi'an also means that a few rounds of testing are unable to detect all infections, the officials said, noting that, for this reason, it is necessary to launch multiple rounds of testing to discover COVID-19 cases and asymptomatic carriers as soon as possible.  

Since the latest spike hit Shaanxi on December 9, a total of 499 locally transmitted cases have been detected as of Saturday with 485 of them in the capital. 

Zhang Boli, an expert of the central leading COVID-19 response group, said that under strict measures, it is possible for Xi'an to cut virus transmission by middle January and put the outbreak under control in late January.