Metro Vancouver wastewater data shows COVID-19 decline after Omicron peak

With daily case counts no longer a reliable indicator of how prevalent COVID-19 is in B.C, wastewater analysis suggests the Omicron wave peaked in early January.

Natalie Prystajecky with the BC Centre for Disease Control says data shows a decline in the concentration of the virus at five Metro Vancouver wastewater treatment facilities. This analysis has been underway since May of 2020, when the number of positive PCR tests reported by the province more accurately reflected how many people in the province were infected.

“We’ve been doing this since the beginning of the pandemic, and what we see is that when there are spikes in cases, we also see spikes in the wastewater,” Prystajecky said.

“We used to see that the case counts and wastewater counts tracked very closely together. But of course now with the testing criteria changing, we don’t see them track as closely together anymore.”

While wastewater alone doesn’t tell the whole story, Prystajecky says evidence strongly suggests cases are on the decline.

“What we are seeing is that we had a peak in wastewater concentrations at the beginning of January, and those counts in wastewater are coming down. They are not down to pre-Omicron levels, they certainly are much lower than they were,” she says.

Public health will use a series of indicators, of which one can be wastewater. So you would not look at wastewater alone. You would look at wastewater in the context of other indicators such as case rates, hospitalizations, ICU rates. It’s one of several tools that can be used. In general, no surveillance indicator is used in isolation.

There are some limits to the data, Prystajecky says, noting not everyone with the virus will shed it through feces and the data lags behind the clinical data by about a week. Currently, wastewater testing is not done in the entire province, but there are hopes to expand it.