A transparent EWMA-based early-warning index for RSV and influenza A from WastewaterSCAN wastewater signals, benchmarked against CDC laboratory surveillance

Abstract Wastewater based epidemiology offers a valuable population level signal for monitoring respiratory virus activity, but its routine use in public health practice requires alerting methods that are transparent, interpretable, and comparable across locations. In this study, we propose a simple early warning framework that transforms wastewater viral RNA measurements into actionable alerts using a standardized statistical process control approach. The method relies on variance stabilization, site specific baseline normalization, and an exponentially weighted moving average to identify sustained increases in viral activity. To support operational relevance, wastewater derived alerts are benchmarked against established laboratory surveillance systems using a harmonized onset definition. The proposed framework emphasizes clarity, auditability and adaptability rather than complex forecasting, enabling straightforward interpretation by public health practitioners. Our results demonstrate that wastewater signals can provide timely situational awareness for respiratory virus circulation and support their use as a complementary tool for public health surveillance and preparedness.