Applications of SARS-CoV-2 sewage surveillance to fight against COVID-19

Abstract

The municipal sewage collection and treatment system in a city is not only an important engineering infrastructure to protect human health, but also a source of information on the health status of the people and the development trend of infectious diseases (such as Corona Virus Disease 2019, COVID-19). After the outbreak of COVID-19, a number of researches and practices on the monitoring and analysis of SARS-CoV-2 virus in sewage have been carried out to assist the fight against COVID-19. Hong Kong's research and experience in using sewage monitoring to control the spreading of SARS-CoV-2 provided an important reference for the development of the methodology in wastewater-based epidemiology, the establishment of technological platforms, and the planning and design of the infrastructure of future cities. The interdisciplinary research team of environmental microbiology, engineering and public health of the University of Hong Kong, with the strong supports and in collaboration with relevant departments of the Government of the Hong Kong Special Administrative Region (SAR), has first developed the laboratory analytical method, then conducted testing and explorations in local communities, and finally established a comprehensive sewage monitoring network for Hong Kong. The analytical method developed by the team consists of a two-step separation step and the detection of two gene segments of the SARS-CoV-2 virus for determining the presence of the SARS-CoV-2 in sewage. The research and development results demonstrated that sewage surveillance could be applied in Hong Kong for the following purposes. (1) Providing early warning signals for COVID-19 outbreak: The research showed that the sewage surveillance results have correlated very well with the fourth wave of epidemic outbreaks in Hong Kong since mid-November of 2020. The detection of viruses in sewage could be used as supplementary information to complement clinical testing to provide early warning signals of community outbreak. (2) Tracking the trend of community outbreak: During the epidemic, the changes in the detection rate of viruses in sewage can be used to assess the trend of the epidemic in the community. (3) Complementing the monitoring of infection clusters in local communities/housing estates: In response to the development of the fourth wave of the epidemic in Hong Kong, the research team flexibly adjusted the monitoring plan, conducted targeted sampling and analysis at buildings/housing estates/street blocks with infection clusters, and provided complementary information for clinical tests. Between 28 December 2020 and 9 February 2021, compulsory testing notices were issued in 26 buildings/street blocks of Hong Kong where sewage test results were positive, including compulsory testing in "restricted areas". More than 50 confirmed COVID- 19 cases were identified, cutting off hidden transmission chains in these communities. The sewage monitoring system of SARS-CoV-2 has now been fully implemented in Hong Kong by EPD (Environmental Protection Department) and DSD (Drainage Services Department), covering over 100 regular sampling sites in Hong Kong, providing early warning signals of COVID-19 re-emergence for over five million people, and has also become an important basis for follow-up epidemic prevention work. Using this system, the HKU team successfully identified the Delta variant in a sewage sample collected on June 21, 2021 from Tai Po, and alerted the first introduction of the Delta variant in the community sewage of Hong Kong before the relevant clinical case was reported. The Government of the Hong Kong Special Administrative Region took quick action according to sewage test results and stopped the transmission. Following the success in the development of sewage testing methods worldwide, the research and developments should focus on better use of in-manhole samplers, selecting the most suitable sewage sampling time windows, simplifying the sample pre-treatment procedure, increasing the sampling and testing capacity, developing new methods for variants, and integrating clinical/ epidemiological data, to further develop the sewage surveillance system into a more powerful tool to facilitate decision-making in fighting SARS-CoV-2. At present, it has been clearly realized that sewage monitoring can play an important role in controlling the spread of diseases. Many cities are gradually establishing and improving sewage monitoring systems and using this system as a part of future smart cities to protect public health from known and new pathogens. Sewage may tell the health of a city, and we are learning how to listen to it.