Asymptomatic COVID-19 infections can't escape nucleic acid testing

Asymptomatic infections, a heated issue in China amid the COVID-19 epidemic these days, would never escape nucleic acid testing and would not show unusual results in tests, a senior testing expert in Shanghai said.

"The test result is a numerical number and it doesn't have anything to do with whether the patient will eventually show symptoms or not," said Li Chongshan, deputy director of the Division of Microbiology under the Shanghai Municipal Center For Disease Control and Prevention, during an exclusive interview with China Daily on Tuesday.

The National Health Commission said on Tuesday that there were 1,541 asymptomatic infections of COVID-19, including 205 imported cases, under medical observation in the country by the end of Monday, and it will scale up screening such cases and expand testing to close contacts of infected patients in an effort to prevent a possible domestic rebound of the outbreak.

Li said seen from Shanghai's data and that of the whole country, asymptomatic infections only accounted for between 1 to 5 percent of the total number of patients so far.

"In more cases, a case that didn't show any symptoms of the novel coronavirus infection when it tested positive for the virus would develop symptoms in several days. That means they were in the incubation period of the virus when taking the test," he said.

Medical experts said usually a person can test positive for the virus through nucleic acid testing two to three days after getting infected.

Also, there are no false-positive or slightly positive COVID-19 cases in final clinical determination, Li said.

"There are actually some test samples, of which the result of the test lasting six to eight hours, that fall into the grey area between positive and negative, and we'll turn to the testing kit of another producer for another test. If both tests show the same results, we'll categorize it a positive case judging from the lab tests," he said.

The Shanghai CDC division has been responsible for producing lab test results for inbound passengers arriving in Shanghai who showed fever or respiratory symptoms and were suspected cases through epidemiological investigations at customs since the municipality beefed up measures to curb the spread of the virus from overseas in early March.

Li said 37 lab workers are divided into groups and working around the clock to ensure test results are produced accurately and efficiently.