National Wastewater Monitoring of Pathogens (NWMP) : Modelling

We update this information on Fridays at 12:00pm Eastern Time. In the event of a holiday, we update on the next business day. Data at some sites may lag for a week or more, due to the time it takes to transport and analyze samples. This report was last updated April 7, 2026 with data up to and including the week of March 30, 2026.

On this page

• Wastewater-based modelling
• Interpreting the data

Wastewater-based modelling

We have developed a wastewater-based mathematical model of respiratory diseases in communities in Canada. Models allow researchers to simulate real-world possibilities in a virtual environment. Using information on how infected people shed respiratory viruses into sewer systems, and how these signals are detected and reported, we can estimate the strength of transmission of a disease in the population at a specific point in time (also known as the effective reproduction number). This information can help support the appropriate public health response.

Interpreting the data

The concentration of COVID-19, flu, and RSV in municipal wastewater can be used to estimate the effective reproduction number (written as “R_t”).

The effective reproduction number (R_t) tells us how strong the transmission of an infectious disease is in the population at a specific point in time. It represents the average number of people that one infected person will pass the virus to.

For example, if the R_t of COVID-19 is 2 in a particular community, this means that, at a specific point in time, on average, each infected person will spread the virus to two other people. R_t does not reflect the current number of infections, so a high R_t value does not necessarily indicate a large outbreak.

• If R_t is above 1: transmission is increasing. Each infected person, on average, infects more than one other person, so the total number of infections is growing.
• If R_t is equal to 1: the number of infections is stable.
• If R_t is below 1: transmission is decreasing. Each infected person, on average, infects less than one other person, so the total number of infections is decreasing.

Figure 1. Graph of effective reproduction numbers, as of {{dynamic-date}} download the data in .csv format

Use the dropdown menu to see estimates of R_t over the last 6 months across different regions in Canada. Hover over the line in the graph to see the mean R_t estimate for a specific day, along with the 95% confidence interval (that is, the range of uncertainty around that estimate). Please see the notes for more information on when there are no R_t estimates on a particular day. Please also note that provincial and national R_t estimates are currently unavailable.

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Notes

• This information is based on data from wastewater samples submitted for testing to the National Microbiology Laboratory.
• When viewing R_t at the collection site level (available in the downloadable CSV file above), estimates are calculated directly from sample concentrations at that specific site.
• When viewing R_t aggregated at the city level:
  • If the city has only one collection site, the city-level R_t is the same as the collection site estimate, based on that site's data.
  • If the city has multiple collection sites, a weighted average concentration, based on the population size of the catchment area of each site, is used to generate the city level R_t estimate.
• The areas in the figure labeled with a red horizontal line indicate periods of low viral concentrations in the wastewater in at least one location, when Rt estimates are considered uncertain. During these periods, estimates are not displayed.
• The horizontal dashed line shows the threshold level “R_t=1” for reference.