COVID-19 Arizona Update – 6/16/20

I continue to focus a bit on my home state, Arizona, due to the attention the large increase in post-easing cases has brought nationally. Over the last week most of the trends have continued.

Summary:

1. Cases continue growing, but it looks like the rate over the last week might be linear. I’ll show data from the two largest counties, Maricopa (Phoenix) and Pima (Tucson).
2. Border cases continue to grow. Santa Cruz county now has a case rate of over 20 cases per 1000 people. This is larger than the case rate for the state of New York. Yuma County’s case rate is 14 per 1000 people.
3. Arizona’s case rate as a whole is under 5 per 1000 people. There have been misleading stories that appear to indicate that Arizona has passed New York in normalized cases. This is only true when one considers the number of cases per person over the last week. Cumulatively, New York’s 19 cases per 1000 people is nearly 4x that of Arizona. Arizona’s case rate puts it at #23 in the nation, whereas New York’s is #1.
4. Arizona’s death rate as a whole is 0.166 deaths per 1000 people. For comparison, New York’s is 1.57 deaths per 1000. Arizona’s death rate is also 23rd in the nation (strange). Our counties range from 0.78 in both Navajo and Apache Counties down to 0.03 in both Graham and Yavapai Counties. Maricopa and Pima are 0.12 and 0.21 respectively.
5. Hospitalization has increased across the board in the state. It’s hard to pin down where exactly the hospitals are filling and where they aren’t due to the way the state shares data. Statewide, ICU bed usage is at 82%, which represents 1,347 ICU beds in use. This is up from 1,192 last week, a difference of 155 patients. Of these, 74, or about 1/2 are COVID-19 (or suspected) patients. When I add up all the hospital bed increases (not necessarily due to COVID patients) over the last month I get a 69% increase. The increase in hospitalization due just to COVID-19 patients was 72%. This sounded very high to me, so I went to the CDC Influenza Tracker site for comparison. The flu season in 2020 saw a one-month 34% increase in all hospital beds across the country (only due to flu). I then looked at what I knew was a bad flu year (2017-2018) and saw a 186% increase in hospitalization due to flu alone that year. One caveat is that one can’t determine what KIND of hospital beds were occupied during this flu season, so hard to compare perfectly to our situation. However, our 72% over the last month is about double the worst flu month this year and less than half of the worst month during a bad flu year. I’ll keep watching the numbers and hopefully it doesn’t keep increasing.

Normalized Cases by Age Group

What I’ve done below is figure out the populations of each Arizona age group below and then normalize the numbers of cases per age group by their population. This allows me to see for a given age group the number of cases per 1000 members of that group. I do the same for Deaths and Hospitalizations.

Interesting things to note:

1. Other than the <20 group, the number of cases per 1000 is pretty close for all other groups. This seems to confirm that the <20 group is much less likely to get infected by COVID. This group has been less tested than the other groups, but the number of tests seems to be a reasonable sample to give a decent estimate for the population.
2. The other metrics (deaths, hospitalizations) differ widely across the different age groups, as one might expect.
3. What this shows is that even at this stage, this disease is still pretty rare (at least per the formal counts). Other than the <20 group, somewhere under 1% of the population has been recorded to be infected. For the Arizona 20-44 age population that is driving most of the new cases, only .04% (of the whole group) has been hospitalized and .003% has died. 4.85% of the confirmed cases in this group has required hospitalization and 0.35% of the confirmed cases has died. Hopefully that explanation helps you read the table. Clearly, getting COVID-19 if you’re over 65 is really concerning (even though only .83% of that population has gotten it yet) due to the 28% hospitalization rate and 16% death rate for people who actually get the virus.

Update on Cases by Demographic

Note that age demographic case trends have continued at pretty much the same rates over the last week. Pima shows a one-day slowdown, but I don’t read much into that yet because it is most likely to be a data collection issue if it doesn’t continue for 3-4 days.

Hospitalizations Compared to Cases

The hospitalization rate (though I showed that it was increasing up above) still looks flat when compared to the case growth. Even though we know that hospitals have limited number of beds, I take this as good because the increase in hospitalization is much, much lower than the increase in cases. In Maricopa we saw about 200 new hospitalizations (only about 40 were ICU beds) to about 6000 new cases over the last week, about 3% of all cases. And looking at the chart, it appears that if trends continue, we’ll be seeing even lower percentages of all cases in the future. Again, this points to a boom in recording less serious cases. It is most likely that this is largely due to the greatly increased number of tests the state has been conducting. These asymptomatic cases may have been around all along but only now are we measuring them. This is why I think looking at hospitalization rates is the best metric now.