Real-time sewage surveillance for SARS-CoV-2 in Dhaka, Bangladesh versus clinical COVID-19 surveillance: a longitudinal environmental surveillance study (December, 2019–December, 2021)
Elizabeth T. Rogawski McQuade, Isobel M. Blake, Stephanie A. Brennhofer, Md Ohedul Islam, Syed Shahnewaj Siraj Sony, Tonima Rahman, Md Hamim Bhuiyan, Sabrina Karim Resha, Erin Wettstone, Lauren Hughlett, Claire E. Reagan, Sarah Elwood, Yoann Mira, Ayesha S. Mahmud, Kawsar Hosan, Md Raihanul Hoque, Md Masud Alam, Mahbubur Rahman, Tahmina Shirin, Rashidul Haque, Mami Taniuchi
Abstract
BACKGROUND: Clinical surveillance for COVID-19 has typically been challenging in low-income and middle-income settings. From December, 2019, to December, 2021, we implemented environmental surveillance in a converging informal sewage network in Dhaka, Bangladesh, to investigate SARS-CoV-2 transmission across different income levels of the city compared with clinical surveillance. METHODS: All sewage lines were mapped, and sites were selected with estimated catchment populations of more than 1000 individuals. We analysed 2073 sewage samples, collected weekly from 37 sites, and 648 days of case data from eight wards with varying socioeconomic statuses. We assessed the correlations between the viral load in sewage samples and clinical cases. FINDINGS: clinical cases increased with time (r = 0·90 in July-December, 2021 and r=0·59 in July-December, 2020). Before major waves of infection, viral load quantity in sewage samples increased 1-2 weeks before the clinical cases. INTERPRETATION: This study demonstrates the utility and importance of environmental surveillance for SARS-CoV-2 in a lower-middle-income country. We show that environmental surveillance provides an early warning of increases in transmission and reveals evidence of persistent circulation in poorer areas where access to clinical testing is limited. FUNDING: Bill & Melinda Gates Foundation.