Longitudinal Surveillance of Mpox in Wastewater at Low Prevalence

This study evaluated wastewater-based epidemiology (WBE) for surveillance of monkeypox virus (MPXV) during the low-prevalence outbreak in Belo Horizonte, Brazil, in 2022. Twenty-nine samples were collected from a wastewater treatment plant between May and December 2022. MPXV DNA was quantified by polymerase chain reaction (qPCR) using 10 technical replicates per sample to enhance sensitivity at low target concentrations. To assess analytical stringency influences surveillance performance, multiple positivity thresholds were defined based on the number of positive qPCR replicates. Permissive thresholds increased sensitivity and early detection but showed limited concordance with reported clinical cases, whereas stringent thresholds improved specificity and predictive value while reducing early detection capacity. These patterns reflect both the low-prevalence context and the absence of a definitive clinical gold standard for validating population-level wastewater signals. Applying the model-based WBE feasibility framework, MPXV shedding was estimated at 8.72 log10 genome copies per day per infection, primarily from skin lesions. Based on shedding estimates and wastewater detection rates, MPXV prevalence and cumulative incidence were estimated to be 1.70–4.87 and 2.81–8.03 times higher than reported cases, respectively. These findings demonstrate that WBE can identify underreported infections and highlight the importance of optimizing analytical thresholds to improve surveillance performance.