The city reported 824 locally transmitted COVID-19 cases, 20,398 local asymptomatic infections, four imported patients and three imported asymptomatic infections on Thursday, said the Shanghai Health Commission on Friday morning.Of all the local infections, 323 confirmed patients were previously asymptomatic infections. Another 121 confirmed patients and 19,798 asymptomatic cases were detected during central quarantine, while the rest were found in the screening of high-risk people.824 local casesThe first 121 patients tested positive during central quarantine.