Iron County Update

The news continued to get worse today, with 15 new positive cases in Iron County.

I wrote yesterday that case growth in Iron County was "worse" than "explosive". Technically, "explosive growth" is not something that is clearly defined. It's just a fun thing to say. And when people see something arcing up on a graph, that's what they call it.

More correctly, we talk about geometric growth or compounding (like interest). Here's some examples with different growth rates:

 

What you get with geometric growth is arcs that get steeper. Eventually they call go close to straight up (like the purple one here), but sometimes it takes a while (like the blue one).

But, if I superimpose Iron County's numbers on the same graph, I get this:

What's concerning about that turquoise curve is that was more or less matching the green curve from  a little after 50 days into the outbreak, until almost 70 days into the outbreak. But recall from above that the green curve would eventually look "explosive". What's happened over the last 10 days in Iron County is that our outbreak has started growing faster than geometric. This means there's something new and special and ... not good ... happening: perhaps travelers introduced new cases, or there was a superspreader event.

Don't forget that I speculated that Iron County will be in trouble when we get up to about 75 cases per week. Looking above, we're at 57 in the past week. An unlucky few of those people are going to be hitting the ICU soon.

One of the reasons we take logs of growing series is because they linearize geometric or compounded growth. If I do this to the hypothetical numbers from the top panel, I get lines of different slopes.

Here's what's important and what's bugging me about our local outbreak. When we take logs, we get lines even when the data might be described as "explosive". But if I add our local case numbers, we see this:

That uptick at the end does not seem large, but that's all our current problem in a nutshell. In short, we were on one path from the early 50's to the late 60's (that was a little flatter than the red line), and over the last ten days we've shifted to a new path that's quite a bit steeper than the red line.

This can also be shown by our days to double, which is now down to seven:

Washington County continues to slowly improve. They had 10 new cases today, but their doubling time has been on the rise for about 2 weeks now.