ポリオ監視戦略で効果的な検出を目指す

タイトル: Assessing early detection ability through spatial arrangements in environmental surveillance for poliovirus: a simulation-based study

概要: Detecting the circulation of poliovirus in its early stages is paramount for swift public health action. Environmental surveillance (ES) is the testing of sewage samples for the presence of poliovirus and has the potential to enhance early detection capabilities. However, the establishment and maintenance of ES sites incur costs and necessitate human resources, underscoring the consideration of ES scale and site selection. Here, we aim to assess the early detection ability of ES by varying the number and location of ES sites using the simulation-based approach. We developed a stochastic meta-population model among unimmunised children aged under 5 years old and used geographic and demographic characteristics of South Africa as a case study of a non-endemic country, assuming a single introduction of wild poliovirus serotype 1. We constructed six scenarios by combining three importation risk distributions (predicated on population size, approximations of international inbound travel volume and border crossing volume) with two ES site layout strategies: one proportionate to population size and another focusing on importation risk via land border crossings. We showed that a modest number of strategically positioned ES sites can achieve a high early detection ability when assumed importation risks were geographically confined. In contrast, when importation risks were dispersed, the effectiveness of ES was diminished. Our sensitivity analyses suggested that the strategy to implement ES across large areas with low sampling frequency consistently resulted in a better early detection ability against various importation scenarios than one to implement ES in limited areas with high sampling frequency. Although we acknowledge the challenges of translating our simulated outcomes for real-world situations, our study has implications for deciding the scale and site selection of ES. Author summaryPoliovirus causes paralytic poliomyelitis, a terrible and debilitating disease. Only a small number of infections with poliovirus result in disease. Early detection of these infections can inform public health decision-makers to trigger interventions such as vaccination campaigns. Environmental surveillance (ES) is able to detect poliovirus circulation by capturing virus shedding (even from asymptomatic people) in wastewater. Strategic geographical placements of ES sites may enhance early detection capabilities, but there has been limited exploration of factors that might affect early detection. Here, we investigated the relationship between the scale and site selection of ES and early detection ability by simulating the introduction, spread and detection of poliovirus among unimmunised children aged under 5 years old. We used geographic and demographic characteristics of South Africa as a case study of a non-endemic country, assuming an introduction of wild poliovirus serotype 1. We found that the informed ES placement achieved a high early detection ability when importation risks were geographically limited. In contrast, when importation risks were dispersed, the ES effectiveness was diminished. Our sensitivity results suggested the strategy to expand ES sites was robust against various importation scenarios and better than the strategy to merely increase sampling frequency in limited locations.