Retrospective Wastewater Tracking of Measles Outbreak in Western Switzerland in Winter 2024.

Measles outbreaks remain a significant public health challenge, despite high vaccination coverage in many regions. Wastewater-based surveillance (WBS) offers a noninvasive and community-level approach to monitoring the circulation of pathogens, including the measles virus. Here, we retrospectively applied a duplex digital PCR assay to distinguish between wild-type and vaccine strains of the measles virus in wastewater samples available from an existing national WBS program. Samples originated from the wastewater treatment plant serving the Lausanne city catchment area, where an outbreak occurred before spreading to the broader Canton Vaud region. Despite high vaccination rates, viral loads of the measles wild type were detected during the first transmission event involving 21 cases identified within a week. However, viral loads were no longer detectable after the initial 21 cases, despite an additional 30 cases reported in the following 3 weeks, possibly due to lower incidence rate or location outside the catchment. Measles vaccine strain was not detected during the outbreak. Our results demonstrate the complementarity of WBS with clinical surveillance and suggest its potential as an early warning system for measles and other vaccine-preventable diseases. Further improvements in the assay sensitivity and integration with epidemiological data could enhance the utility of WBS for outbreak detection and control.