Characterizing Environmental Surveillance Sites in Nigeria and Their Sensitivity to Detect Poliovirus and Other Enteroviruses

Background Environmental surveillance (ES) for poliovirus is increasingly important for polio eradication, often detecting circulating virus before paralytic cases are reported. The sensitivity of ES depends on appropriate selection of sampling sites, which is difficult in low-income countries with informal sewage networks. Methods We measured ES site and sample characteristics in Nigeria during June 2018-May 2019, including sewage physicochemical properties, using a water-quality probe, flow volume, catchment population, and local facilities such as hospitals, schools, and transit hubs. We used mixed-effects logistic regression and machine learning (random forests) to investigate their association with enterovirus isolation (poliovirus and nonpolio enteroviruses) as an indicator of surveillance sensitivity. Results Four quarterly visits were made to 78 ES sites in 21 states of Nigeria, and ES site characteristic data were matched to 1345 samples with an average enterovirus prevalence among sites of 68% (range, 9%-100%). A larger estimated catchment population, high total dissolved solids, and higher pH were associated with enterovirus detection. A random forests model predicted good sites (enterovirus prevalence >70%) from measured site characteristics with out-of-sample sensitivity and specificity of 75%. Conclusions Simple measurement of sewage properties and catchment population estimation could improve ES site selection and increase surveillance sensitivity. Easily measured environmental surveillance site characteristics, including sewage properties recorded with a water-quality probe, predict site sensitivity to detect poliovirus and other enteroviruses. Data collection during site selection could identify better sites and improve the sensitivity of global poliovirus surveillance.

Automated summary

This study suggests that measuring sewage properties and estimating catchment population can improve the selection of environmental surveillance sites and increase surveillance sensitivity for poliovirus and other enteroviruses.