There has been a lot of talk about the high positivity rates for COVID testing in BC. In a recent chat @dancoombsUBC hypothesized that the rise in positivity might (in part) be explained by a drop in other respiratory viruses. And I think he is right. Some supporting evidence:

People get tested because they have symptoms consistent with COVID. But same symptoms are also consistent with other respiratory viruses. If lots of people catch other viruses and get tested for COVID, positivity goes down. If only a few catch other viruses, positivity goes up.

Let's look at positivity rates we finally got an update yesterday. The positivity rate (the dotted line) has risen sharply starting around early October. What happened? Covid cases rose during that time, but what happened to other respiratory viruses?

Time to look at the BCCDC Influenza Surveillance Bulletin. This figure shows that this year pretty much the only respiratory virus around are Entero/Rhinoviruses. And their prevalence indeed declined in early October (epi week 41).

Comparing to the previous year’s data we see that Entero/Rhinoviruses also declined, although not as much. But other respiratory viruses rose sharply during this time starting "flu season", which we managed to suppress this year, with those viruses also affected by our measures.

Of course this is not a normal year, and just looking at viruses that got picked up in samples that got tested is not the best measure. Indeed, this year we tested a lot more for all kinds of viruses, not just covid. Which makes the comparison even more startling.

MSP claims are a more robust measure. In Oct we see an unusual rise. That’s COVID cases, which are included in MSP claims, ramping up. But then claims decline below predicted levels in Nov. COVID is still up, but as we saw above, other respiratory viruses are unseasonably low.

It would be great to have the underlying data, that would make it easy to check just how much of change in positivity is explained by this. It would also be good to look at age-specific data to benchmark against @LetsFishSmarter's data scrapes. https://twitter.com/LetsFishSmarter/status/1350279154013331458?s=20