HOUSTON, Nov. 15 (Xinhua) -- U.S. Harris County on Sunday launched a door-to-door survey and antibody test to figure out who has been infected with COVID-19 without knowing it.

According to local media, public health workers on Sunday knocked on the doors of hundreds of randomly selected homes in parts of Harris County where the country's fourth largest city of Houston is located. Houston has done a similar project so this time houses were chosen outside of Houston.

During the process, the team asked residents to answer a brief survey and voluntarily gave a blood sample to be tested for COVID-19 antibody. Deborah Bujnowski, data analytics manager for Harris County Public Health, told a local TV station that the effort was to "determine the extent of community spread of COVID-19."

The doctor also hoped the survey and test results will give a clearer picture of how often people with COVID-19 have mild or no symptoms. "This will help us to inform future prevention strategies," said Bujnowski.

Texas has seen a rapid increase in COVID-19 cases and hospitalizations in the past weeks. In Texas, the most confirmed cases are from Harris County. According to the Texas Health and Human Services, as of Saturday, there were 172,763 confirmed COVID-19 cases reported in the county.