Genotype-Specific Detection of Measles Virus Using Wastewater Surveillance — Wisconsin, February 2026

In February 2026, two travel-associated cases of measles were reported to the Wisconsin Department of Health Services (WDHS). Public health investigations for each case included wastewater (sewage) surveillance for wild-type measles, which was first implemented by the WDHS Wastewater Monitoring Program in June 2025. The virus from one case, caused by measles genotype D8, was detected by a wastewater surveillance assay before the case was identified by local health authorities, leading to public health notifications and action. Measles virus from the second case, caused by measles genotype B3, was not detected by the assay. Additional analysis of the measles wastewater assay, which is among the most widely used assays in the United States, revealed that the assay was not able to detect an internationally circulating variant of the measles B3 genotype. Two alternative assays confirmed that measles virus was present and detectable in the wastewater. The assay developers designed and released a modified assay that incorporated an additional probe that could detect the B3 variant. These cases demonstrate the potential benefit of wastewater surveillance in detecting wild-type measles virus from a single case, while also highlighting the importance of regularly monitoring wastewater assays with respect to available genomic data. These activities should be supported by up-to-date libraries of publicly available whole-genome sequencing data.