Abstract
In September 2023, the North Carolina Department of Health and Human Services identified a new case of mpox clade II 5 months after the last previous report. To assess possible unrecognized transmission, nonvariola orthopoxvirus testing was implemented at select wastewater sites. During October 29, 2023-May 2025, a total of 801 samples were collected across 16 treatment plants serving ≈2 million residents. We analyzed wastewater detections (n = 47) and clinical cases (n = 45) using a +17-day window. Overall sensitivity of identifying the presence of >1 temporally aligned mpox case within a sewershed was 10.6% (95% CI 6.5%-16.7%); specificity was 95.1% (95% CI 93.2%-96.5%), positive predictive value was 31.9% (95% CI 20.4%-46.2%), and negative predictive value was 83.2% (95% CI 80.3%-85.7%). Restricting detections above the limit of detection reduced sensitivity but increased specificity. Overall, wastewater surveillance showed low sensitivity but provided complementary awareness for public health response.