Shanghai will launch another round of citywide nucleic acid testing on Tuesday to continue screening out positive COVID-19 cases, with the goal of soon achieving zero community transmissions.

Every resident in the city's locked-down, controlled and precautionary areas will take a polymerase chain reaction (PCR) test tomorrow despite predicted rainfall, said Zhao Dandan, deputy director of the Shanghai Health Commission.

Door-to-door sample collection will be provided for those who have tested positive via antigen self-tests and are awaiting rechecks, as well as people living with them, Zhao said.

Everyone must wear masks and maintain two-meter social distancing to reduce the risk of cross infections.

The city reported 19,455 positive infections on Sunday, 7 percent less than Friday.

The number of community transmissions is also gradually falling. A total of 217 such infections were found during PCR screenings in local communities on Sunday, 20 percent lower than Saturday.

138 deaths

Shanghai reported 51 COVID-19 deaths on Sunday – one-third more than Saturday – bringing the total since the resurgence commenced in March to 138.

The average age of Sunday's fatalities was 84.2, and the oldest was 100. All had severe underlying conditions, and only four had been vaccinated.

Among Shanghai's COVID-19 patients, 196 have severe symptoms and 23 are in critical condition, a 20 percent increase over the previous day.

Meanwhile, a total of 21,972 COVID-19 patients were discharged from local designated and makeshift hospitals on Sunday after making full recoveries, an increase of more than 16 percent over the previous day.

Antigen self-testing cannot replace PCR testing, which is more accurate, said Hu Xiaobo, director of the Shanghai Center for Clinical Laboratory.

However, that accuracy can be affected by other processes, such as sample collection, transport and testing, Hu noted.

He added that frequent PCR testing is designed to detect infections in incubation periods with viral loads that are too low to result in positive results in a single test.