Environmental Surveillance of Poliovirus in the Democratic Republic of the Congo: Sensitivity and Site Productivity, 2017–2025

Background: Environmental surveillance (ES) of wastewater was introduced by the Global Polio Eradication Initiative (GPEI) to improve the sensitivity of acute flaccid paralysis (AFP) surveillance. In the Democratic Republic of the Congo (DRC), ES for poliovirus has been implemented since 2017. This study assessed its sensitivity and productivity. Methods: A retrospective descriptive study using ES for poliovirus data collected in the DRC between September 2017 and June 2025. Wastewater samples were analyzed at the National Institute for Biomedical Research (INRB), using a standardized algorithm that included concentration, cell culture, real-time reverse transcription polymerase chain reaction (rRT-PCR), and VP1 sequencing. Site sensitivity was assessed by productivity, defined as a viral isolation rate ≥ 50%. Results: A total of 2491 wastewater samples were collected. ES expanded from 6 sites in 3 provinces to 27 sites across 8 provinces. Overall site productivity was 33.9% (846/2491 cultures positive for enteroviruses), showing significant variability between sites and over time, which sometimes led to site closures. Non-polio enteroviruses were the most commonly isolated viruses. Among poliovirus isolates, Sabin-like strains (types 1, 2, and 3), novel oral poliovirus vaccine type 2 (nOPV2), and vaccine-derived poliovirus type 2 (VDPV2) were identified, with VDPV2 representing 13.1%. No wild poliovirus was detected. Conclusion: ES for poliovirus has expanded in the DRC, helping detect vaccine-derived poliovirus circulation and confirming the absence of wild poliovirus. Despite ongoing operational and logistical challenges causing fluctuations in site productivity, this study emphasizes the vital role of ES as a supplement to AFP surveillance.