I haven’t looked at the zip code data in a little while so I was curious to see if the case growth was coming from different places. Here’s the top 20% of zip codes by case growth in the last month and a half (Note that I’m not showing the growth percentages… they range from 945% down to about 350% in these locations). Interestingly, some of the areas with the lowest case growth are the border counties that had the highest case growth back on 6/14. This indicates, obviously, that case growth is slowing in these counties.
This is a more interesting way to look at the data than I had suspected. I add another dimension to the visualization by only including the top 20% of zip codes by case growth. Now we can see total number of cases (the color), the size of the zip code (bubble diameter) and case growth (the fact it’s on this chart).
What do we notice here?
1. We can see that a handful of zip codes with medium numbers of cases are apparently growing fast (the light green and orange).
2. We can also see that there’s large case growth on the fringes of the Phoenix metro area in zip codes that hadn’t been affected much (dark blue bubbles). This appears to include a handful of wealthier zip codes.
3. There is also a pretty large cluster of cases now in the East Valley of Maricopa County that didn’t exist before. This cluster stretches down to Florence, the location of the State Prison, which had a large number of cases per capita a month ago.
4. Both Pinal and Pima county are mostly absent from the top 20%, with only a couple of zip codes in Pinal (San Tan Valley and Apache Junction) and one zip code in Pima (Oro Valley) included. In the case of Oro Valley, the zip code (85737) just barely broke my 100 case limit for consideration, so their growth has been small in numbers, but larger in percentage.
5. Some of the large SW Phoenix zip codes (Maryvale, Laveen, Tolleson, South Mountain) are now missing from the top growers. This goes the same for the border counties in Yuma and Santa Cruz Counties
Conclusion
I have been wondering if there’s a mechanism that the virus “burns itself out” in a region/population. Perhaps there are some people who are many times more susceptible of getting infected who get infected first and then eventually things tail off. There could be a number of reasons for this: pre-existing conditions, personal and work situations, and perhaps even mild immunity coming from memory in T-cells or other mechanisms in the immune system (this seems pretty likely to me for a number of reasons… see this link from Nature.com). For whatever reason, the chart above does present the possibility that the current outbreak has burned out (new number of cases per day has slowed) in the previous AZ hotspots.