Rates of influenza A and respiratory syncytial virus (RSV) are both on the rise in Toronto, sewage-testing data shows.
The rates for both viruses seem to follow a traditional pattern seen in previous years where prevalence spikes during the winter months.
The Ashbridge's Bay Wastewater Treatment Plant, where the samples were taken, handles sewage from Toronto's downtown, and from the east and west ends of the older part of the city.
The data is current to the first week of January.
Influenza A shot up dramatically in the first week of December, more or less tracking trends seen in the sewage data at the beginning of last winter.
The graph for RSV looks similar. Most people experience RSV as a cold, but it can be more dangerous for babies, the elderly and people who are immunocompromised.
Influenza B spiked in the winter of 2023-4, but not the winter of 2022-3 or, so far, this winter.
Systematic testing of sewage for diseases began during the pandemic.
It offers an alternative to relying on medical data, like positive tests, for tracking disease in a community.
Not every person with a given disease ends up tested for it, or experiences symptoms serious enough that they seem medical attention. Sewage, however, offers the possibility of a data source that everybody — young or old, rich or poor — participates in creating.
As a data source, sewage can also provide earlier signals than test results. Often, people are sick for a few days before seeking medical attention, and there can be further delays before a positive test result ends up in the statistics.
In New Haven, Ct. in April of 2020, for example, samples from local sewers showed COVID trends a full week before they showed up in public health statistics based on tests.
Controversially, Queen's Park shut down the province's wastewater testing unit in June. It previously hosted 58 testing locations spread out across the province's regions, including 18 in northern Ontario.
Now, a much smaller federal program tests at seven Ontario sites: four in Toronto, two in London and one in Mississauga.
