Pierce County Health Department On Sept. 24, 2025, Washington State Department of Health (DOH) and the University of Washington detected clade I mpox virus (also called monkeypox virus) in Pierce County wastewater. After consultation with Centers for Disease Control and Prevention (CDC), Tacoma-Pierce County Health Department is working with DOH to increase wastewater testing to monitor the situation. At this time, no patients with clade I mpox have been reported in Pierce County.
Two types of virus cause mpox: clade I and clade II. The vast majority of mpox cases in the United States have been caused by clade II mpox. According to CDC, six cases of clade I mpox have been reported in the United States in people who had recently traveled to countries with ongoing outbreaks. So far, there has not been sustained transmission of clade I mpox reported in the U.S.