A smaller proportion of Shanghai's new COVID-19 positive cases have been detected during nucleic acid screening among high-risk groups, though the total daily number of new cases remains high.Some 97 percent of the city's 24,820 new positive cases reported on Saturday were found among those who were already under central quarantine or were previously asymptomatic infections.The rest of the 307 confirmed cases and 415 asymptomatic cases were newly detected during the ongoing massive polymerase chain reaction (PCR) testing, according to Wu Jinglei, director of the Shanghai Health Commission.