As Canada grapples with its largest measles outbreak in over ten years, health experts suggest that a tool utilized during the COVID-19 pandemic could aid in controlling the spread.
Wastewater surveillance, a method involving the testing of sewage samples for viral pathogens, proved invaluable during the pandemic. The data gleaned from this process assisted overwhelmed health authorities in tracing the trajectory of COVID-19 and foreseeing case developments.
Initially hailed as a crucial public health instrument capable of serving as an early warning system against future harmful infections, wastewater surveillance is now being recommended by experts as a potentially beneficial resource in combating the current measles outbreak, which has exceeded 500 cases in Canada.
Despite the potential advantages, public health officials have not actively employed this tool to detect measles. In Ontario, a region heavily affected by measles, wastewater surveillance has been reduced, with the province discontinuing its program last summer. Instead, Ontario plans to rely on the Public Health Agency of Canada (PHAC), which operates a wastewater monitoring dashboard aggregating data from various sites nationwide.
However, the current PHAC dashboard does not monitor the measles virus. While the agency tracks weekly measles case counts and discloses them online, there are no immediate plans for additional surveillance through wastewater. Measles is considered a nationally notifiable disease in Canada, warranting high-level monitoring.
Similar to COVID-19, individuals with measles can be asymptomatic but still contagious, indicating that reported cases may be underestimated. Wastewater surveillance could play a significant role in pinpointing areas where the measles virus is prevalent, enabling the implementation of targeted public health measures.
Studies, such as one conducted in Ottawa earlier this year, have underscored the potential of monitoring measles through wastewater surveillance, emphasizing its complementary role in existing public health strategies.
Mike McKay, director of the Great Lakes Institute for Environmental Research in Windsor, Ontario, has been actively testing wastewater for various viruses, including COVID-19. Collaborating with PHAC, his team has extended testing to include measles, responding to requests from health officials in Detroit and southwestern Ontario.
McKay emphasizes the importance of early detection, particularly for measles, as infected individuals can shed the virus before showing symptoms. While PHAC has not yet requested measles testing from McKay, informal agreements have enabled testing in specific regions.
Despite the recognized benefits of wastewater surveillance, limited testing sites remain a challenge. PHAC’s varying site coverage, with a predominant focus on COVID-19, underscores the need for expanded surveillance efforts, especially during outbreaks like the current one in Ontario.
The potential delay in sequencing signals from live-attenuated vaccines used against measles poses a testing hurdle. Distinguishing between vaccine and virus signals requires additional sequencing, prolonging the testing process.
The necessity for enhanced surveillance is emphasized by the current measles outbreak’s origins, traced back to a large gathering involving Mennonite communities in New Brunswick. The outbreak has since spread to multiple regions, with southwestern Ontario bearing a significant burden.
Areas with under-immunized populations, such as Mennonite, Amish, and other Anabaptist communities, are particularly vulnerable to measles outbreaks. Despite the absence of active wastewater monitoring in these regions, experts stress the critical role of surveillance in effectively managing outbreaks and informing public health responses.
