Post #687: ZIP level map of coronavirus cases per 10,000

COVID-19 Cases per 10,000 by Northern Virginia ZIP code, as of 5/11/2020.  Vienna, VA (ZIP 22180) is the blue dot.

Sources:  Case counts by ZIP code are from the Virginia Department of Health.  Population by ZIP code is from https://simplemaps.com/data/us-zips .  Map is via Bing Maps.

The measles chart above shows the density of diagnosed COVID-19 cases per 10,000, for all ZIP codes in Northern Virginia with at least 5,000 total population.  (Which is, in fact, almost all of them).  The larger the dot, the higher the density of cases.  Vienna (ZIP 22180) is in blue.

This is a little hard to take in by eye, because the only thing that matters is the size of the dots, not the spacing.  You want to focus on where the dots are big, not where they are close together.

By eye, the only thing that seems clear is the correlation between high density of cases per 10,000, and high population density.  The heavily urbanized areas in the close-in DC suburbs have generally higher rates of COVID-19 cases than the less-densely populated areas.

But as a lifelong NoVA resident, I think I see “blue collar” in this chart as well.

Point 1:  Look west on I-66, and you see a big red dot where the road curves.  That’s in the Manassas area, in a part of town that was light industry and retail, but has added a large amount of medium-density housing (apartment buildings, townhouses) in the past decade or so.  (E.g., there’s a big Salvation Army thrift store there, which tells you that it’s not an upscale neighborhood.)  This is a view of the center of that ZIP code.  The large gray blocks are a mix of apartments, condos, and townhouse developments.

Point 2:  The big red dot next to that, I know well, because that’s where I grew up:  That’s the Westgate/Sudley/Yorkshire areas of Manassas.  When I lived there it was a middle-class blue-collar community, and it has gone downhill since it was built in the 1960s and early 1970s.  Here’s a typical dwelling.  No great shakes, and the owner probably isn’t a doctor, lawyer, or business executive.

Point 3:  Springfield.  Here, I’m less sure.  Springfield was and is a significant commercial hub for this area.  But in addition, they are the home of the single largest assisted-living/senior-living development in the area, Greenspring.  So I don’t want to generalize there, because I don’t know whether the high rates there might be driven by having such a large concentrated senior-living facility in that area.

In any case, if you look at our own little patch of upscale living — Oakton, through Vienna, and then on up into McLean — you see nothing but small dots.  I’d attribute that to a combination of low-density housing and high-income earners.   Plausibly, we are rich in the sort of families that can effectively shelter in place with minimal outside contact, and that keeps our overall infection rate low.

My guess is that much of the spread outside of the home, at present, is spread in the workplace.  (I mean, just look at the White House).  It would be helpful if the Commonwealth’s epidemiologists could confirm that.

My conclusion is largely based on the age distribution of the known infections.  The elderly are far more susceptible to serious (reportable) infection, and so you would think that the peak infection rate would be in the retiree population.  But, in fact, aside from the very oldest old, the peak infection rate actually occurs in the working-age population.   That, and the negative statistical association between ZIP-level infection rate and income (prior post), both point to the workplace as a likely vector for infection.

I hope that people eventually figure that out, take it to heart, and wear a mask at work.