Update on Maricopa and Pima COVID Cases. Above is the chart I showed a few weeks ago. Not much has changed but here’s what I can see:
1. Cases are now growing at a noticeably lower rate than they were a week or 2 ago in Maricopa. Pima County rate is also lower. Note, though, that both are still increasing. Just at a lower rate. This COULD be a sign of a flattening or maybe it’s just a pause.
2. Tests have decreased (yellow dashed line) since the peak. This is kind of a chicken and an egg thing. It could be that less tests are being done therefore we have less cases confirmed. OR, it could be that there are fewer people feeling sick and therefore less people getting tests. We can’t really know since the state doesn’t have a randomized testing strategy.
3. From the state’s data dashboard, the percent of tests that are positive is still around 12% (and the trend is decreasing). This may be the source of our County Supervisor’s mysterious 11% “transmission rate” that he announced in the letter that recommended schools not reopen… If so, it’s not a very good metric for much of anything, much less school reopenings. All it means is that 12% of the people in the state who feel sick and get a test are coming up positive for COVID. The problem, again, is that the testing is biased towards people who feel sick or who work in professions where there’s a high likelihood that they will get exposed. I won’t go into it, but you can probably imagine other reasons why this isn’t a very solid metric.
4. If you look closely at either the Maricopa or the Pima County datapoints, you’ll note that the acceleration trend turned into a deceleration trend around July 2nd. This was hard to see until recently, but it seems pretty clear now. The interesting thing is that July 2 is about 2 weeks after both counties made a mandatory facemasks in public proclamation. This is pretty interesting and provides some measure of evidence of the impact of facemasks on a region’s case numbers. Of course it’s just an unplanned natural experiment and I can’t find a good control county (i.e., no facemask proclamation) to compare to. But still, interesting.
In the chart above, I’m showing the death trends since 6/13 by the youngest 3 demographics. Blue is under 20, red is 20-44, and yellow is 45-54. I’m leaving out the folks over 55 because their death rates are higher than these three and make these 3 look very minimal. Note that each of these groups has ~200 deaths or fewer since the start of the outbreak. The interesting thing to me is that the older two groupings both have slight exponential growth (curving upward). You can see this by the 2nd order polynomial fit that is about as close to perfect as a curve fit can be. The x-squared term shows the small magnitude of the acceleration of these rates. HOWEVER, the under 20 group is best fit with a straight line. It is not exponentially growing and indeed is barely growing at all. There could be a bunch of reasons for this, but I find it very interesting. First, many individuals in this group are more likely better protected because they’re not going to school, to the grocery store, or to camps (because most of those have been cancelled). Maybe this would mean that when they get infected it is with a lighter dose? Second, however, it is possible that this is an indicator of what the papers are suggesting and that is that people under 15 are relatively unaffected by this virus.
Above is the similar hospitalization chart for these 3 groups. When I fit the data points on the hospitalization chart, all three age groups are a linear fit. This means that though cases are accelerating and deaths are accelerating (slightly) for the older two groups, the hospitalization rates are steady. I presume that has something to do with the load management ability of hospitals.
The above shows these numbers normalized by the population of each age grouping in Arizona. How to read this: Looking at the Under 20 column, this says that 9 out of 1000 people under 20 have had Confirmed COVID-19 Cases. 1.02% of these people with confirmed cases (.0927 out of 1000 people in the group) were hospitalized. 0.06% of the people in this group with confirmed cases died (0.0051 out of 1000 people in the group).You can see why I don’t show this chart much… in many cases the numbers are really too small to wrap our brains around. To help with understanding this, raw numbers for the under 20 demographic since the start of the outbreak are 11 deaths and 199 hospitalizations out of a population of 2.15 million people under age 20. * Note that the numbers the state provides for hospitalization by demographic seem to be in bad shape… not sure how trustable they are right now.
I am curious about your first graph. When I look at the EPI curves on the ADHS site they show a marked decrease. When I look at reported deaths, it looks like not much change. How can that be? If I understand the reported deaths number, it is not “deaths yesterday” but accumulated deaths from previous weeks newly reported. That is why the EPI looks different. How did you make your calculation?
Hi Mark! The EPI curves on the AZDHS site are always behind… Not sure exactly why this happens, but you’ll see about a week (or even two) lag in data. This artificially makes the recent numbers seem very low.