Shanghai will launch another round of citywide nucleic acid tests or antigen self-testing on Wednesday for additional COVID-19 screenings after previously detected positive cases were transferred to central quarantine.Residents in communities where any positive case has been detected since April 1 will receive a polymerase chain reaction (PCR) test today. These communities or companies will be listed as key areas. A mixed sampling for every 10 people will be conducted.Courier staff, meal deliverymen and other urban service personnel who are still moving around will receive a PCR test in their communities today with individual samplings.