Use of Sewage Surveillance for COVID-19: A Large-Scale Evidence-Based Program in Hong Kong

BACKGROUND: Sewage surveillance, by detecting SARS-CoV-2 virus circulation at the community level, has the potential to supplement individual surveillance for COVID-19. However, to date, there have been no reports about the large-scale implementation and validation of sewage surveillance for public health action. OBJECTIVE: Here, we developed a standardized approach for SARS-CoV-2 detection in sewage and applied it prospectively to supplement public health interventions. METHODS: We analyzed 1,169 sewage samples collected at 492 sites from December 2020 to March 2021. Forty-seven of 492 sites tested positive, 44 (94%) of them had traceable sources of viral signals in the corresponding sewershed, either from previously unsuspected but subsequently confirmed patients or recently convalescent patients or from both patient groups. RESULTS: Sewage surveillance had a sensitivity of 54%, a specificity of 95%, a positive predictive value of 53%, and a negative predictive value of 95% for identifying a previously unsuspected patient within a sewershed. Sewage surveillance in Hong Kong provided a basis for the statutory public health action to detect silent COVID-19 transmission. DISCUSSION: Considering the epidemiological data together with the sewage testing results, compulsory testing was conducted for individual residents at 27 positive sewage sites and uncovered total of 62 previously unsuspected patients, demonstrating the value of sewage surveillance in uncovering previously unsuspected patients in the community. Our study suggests that sewage surveillance could be a powerful management tool for the control of COVID-19.