Clade I Mpox Detected in Pierce County, Washington, Wastewater
October 8, 2025
The detection of clade I mpox virus in Pierce County wastewater marks a significant early warning for Washington State’s public health system. While no human cases have been identified, the collaboration between the Department of Health, the University of Washington, and the Tacoma-Pierce County Health Department demonstrates proactive surveillance in action. Wastewater testing provides a critical tool for detecting emerging threats before they reach clinical settings. Ongoing monitoring, transparency, and readiness will be essential to prevent potential transmission. This discovery reinforces that vigilance and interagency cooperation remain key to containing evolving infectious diseases such as mpox.
The identification of clade I mpox virus in Pierce County wastewater underscores the growing importance of wastewater surveillance as an early detection tool for infectious diseases. The Washington State Department of Health (DOH) and the University of Washington’s testing program found traces of the virus in samples collected in September, prompting swift coordination with the Tacoma-Pierce County Health Department and the U.S. Centers for Disease Control and Prevention.
Clade I mpox, historically associated with higher severity and mortality rates than the clade II strain seen during the 2022 global outbreak, has primarily circulated in Central and East Africa. Its detection in U.S. wastewater highlights the need for continued vigilance, even in the absence of confirmed clinical cases. Currently, no patients with clade I mpox have been reported in Pierce County, but public health officials have expanded wastewater monitoring to track potential spread and identify any emerging risk patterns.
This event illustrates how modern disease surveillance has evolved beyond traditional case reporting. Wastewater monitoring allows scientists to detect viral fragments shed by infected individuals—often before symptoms appear—providing valuable lead time for containment. Similar methods proved crucial in tracking SARS-CoV-2 and now serve as an early warning system for other pathogens, including mpox.
The rapid, coordinated response between state and local health departments, academic researchers, and federal partners reflects a strong model for public health preparedness. Continued investment in wastewater surveillance, community communication, and laboratory capacity will be vital to stay ahead of emerging threats. While the current risk to residents remains low, the Pierce County detection serves as a reminder that global outbreaks can have local implications, and early action is the cornerstone of prevention.