Switching to Wastewater Monitoring Only

Case counts were already somewhat misleading so, if people were actually paying attention to the wastewater and had a target and/or threshold for concern, that would actually be potentially a more reasonable thing to monitor... with that in mind, let's look at some time points to try to find some measures to consider.  Let's start with establishing a few thresholds.  

Early on in the pandemic, we said 8 cases per 100,000 people per day was the highest threshold of concern (ie, that was the introduction to the highest risk-rating we had).  Later, we relaxed this a bit because we realized that this would keep us on high alert and never allow us to go back to normal ... sort of like saying that everybody is smoking so the threshold that for risking cancer shouldn't be smoking 3 cigarettes a day but instead should be a pack a day.  Based on this relaxing of concern, let's go ahead and add in 16 cases per 100,000 people per day as a threshold to monitor for, just as we did with case tracking.  Also, we can look at things like when we got really low... like the low we saw in 2021 of just under 1 case per 100,000 people per day in June.  I don't expect we'll ever reach this threshold again but if we did, we could celebrate a bit.  

We shouldn't start until we have relatively frequent wastewater tracking data points (1 data point doesn't give us a great average to review).  Also, keeping in mind that testing dropped off throughout 2022 as we got used to testing at home, we should probably stop after mid-2022 for pulling out wastewater points.

First thing to do is collect some data.

Date range for 7-day average 7.5-8.5 cases per 100,000 people per day (the average of the readings of copies per mL range for these days south ; north):

• 28-Sep-2020 through 07-Oct-2020 (55.6 ; 41.2)
• 12-May-2021 through 13-May-2021 (57 ; 61)
• 26-Jul-2021 through 27-Jul-2021 (268.5 ; 222)
• (that's it... we wouldn't see ourselves testing this low until 2023 when we were no longer testing consistently)

The wild variation between the first pair vs the final set of readings suggests that by July 2021 we had stopped testing as much, which makes sense given the messaging that we've had where, if you're vaccinated, you're safe.  This is also a time period where we were transitioning away from testing in controlled settings and instead only testing at home.  So, let's toss the July 2021 and stick with the early comparisons.  This would suggest we would want to see around 50-60 copies per mL to compare to the original start of highest risk in our communities.

Date range for 7-day average 15-17 cases per 100,000 people per day (the range of 7-day average copies per mL range for these days south ; north):

• 26-Oct-2020 through 01-Nov-2020 (126.9 ; 146.3)
• 26-Apr-2021 through 29-Apr-2021 (184 ; 124)
• 10-Aug-2021 through 15-Aug-2021 (299.7 ; 382.5)
• (given that we see a dramatic shift in August, I'll stop reviewing the data

So, the revised 16 cases per 100,000 people per day threshold for concern that we moved to for the sake of returning to business as usual is probably somewhere around 125-150 copies per mL.

Date range for 7-day average <1 case per 100,000 people per day (the range of 7-day average copies per mL range for these days south ; north):

• 21-Jun-2021 through 26-Jun-2021 (11.7 ; 22)

Summary:

We should target around 10-20 copies per mL to achieve what we know is possible.

We should see below 50 copies per mL as moderate risk.
We should view 50-60 copies per mL as moderate-high risk (the original entry to "red" in the 3-color risk coding)

We should consider 125-150 copies per mL as a threshold for concern and anytime we're there or higher we should increase our precautions dramatically (as this has been the CDC's threshold for concern when viewing cases-only)

You might be wondering where we are now.  The 7-day average from the latest reading (2-May) sits at 158 copies per mL for the southern region and 205 for the northern region.  Putting us right around the lowest spread we've seen in the last year but still significantly higher than what has been considered safe.