A Single Outbreak Completely Skews Your Perspective
San Francisco’s Zip Code Dashboard.
Western Addition Looks Hot Compared to Surrounding Zip Codes.
The Western Addition neighborhood on the above map zip code 94115 looks hard hit by COVID-19 when compared to the surrounding neighborhoods. As shown in the popup statistics box, that neighborhood has 77 cases and a population of 35,751 giving it a case rate of 21.5 cases for every 10k residents. Four of the five adjacent neighborhoods have case rates of 10 or fewer.
One Single Substantial Outbreak at Central Gardens Changes Everything.
There has been great reporting on the outbreak at the Central Gardens, Mission Local on Central Gardens. Looking through this reporting you see that in this single outbreak 65 people tested positive. What did this outbreak do to the case rate in the 94115 zip code? To see the effect lets back-out those 65 cases from the 77 in that neighborhood. With the outbreak the case rate was a 21.5 which is high. Without this outbreak the underlying case rate is 3.4 giving this neighborhood one of the lowest case rates in the city. It changes your perspective on what is going on on the ground.
One caveat to the above calculations is that 27 of the 65 positive tests were of staffers. Were these positive cases tallied under where the staffer caught the disease, zip code 94115, or were they tallied under where the staffer lives. If the staffer lives outside of the city on in a different zip code, is that really an accurate reflection of the true spread of COVID-19 inside the city?
South of Market Case Rate and the Multi-Service Center South Outbreak
One of the hottest regions of the city is the 94107 zip code south of market with a case rate of 30.4. This is also the zip code that contains the Multi-Service Center South Homeless shelter which had a substantial outbreak in which 70 people tested positive. Lets back-out the 70 cases from the 91 and we calculate that the baseline case rate for this zip code is 7 which compares favorably with the other zip codes in the city.
One outbreak dramatically affects the statistics for an entire neighborhood. The two outbreaks taken together account for over 10% of San Francisco’s entire case load.
UCSF Study: Same Effect All Over Again
If you’ve been paying attention to this website, you know how excited I am for the UCSF study around Garfield park and how much I’m working to make it a success. However I realized that this study could substantially skew all the numbers on San Francisco’s dashboard that I’m paying attention to. Furthermore there’s not currently enough information on the dashboard to clean things back up. The study is aiming to test all 5,700 people in the census tract around Garfield Square park. San Francisco has only tested a total of 12,500 individuals to date. If the study is even a modest success, the volume of new samples will overwhelm and disrupt the current baseline.
Two Proposals to Fix Things
Document substantial outbreaks and/or testing events on San Francisco’s dashboard. If more that 15 people are connected in a single outbreak and the city responds with massive testing (as it should) that action should be documented on the dashboard with complete statistics. An extraordinary testing event like the UCSF Garfield park study should be documented on the dashboard with the statistics uploaded. This would allow people like myself trying to dissect the numbers to separate out the spread of COVID-19 through the general population from the spread through susceptible populations or from artifacts like additional testing.
Add more information to the testing dashboard. The testing data should be sliced and diced much more finely. At a minimum it should have symptomatic and asymptomatic categories. It should also have categories for demographics.
We are entering a more complicated phase of this disease and our reaction to the disease. The data collection and the statistics and the modeling are getting harder. Now is the time when solid information becomes even more critical and you need a lot of focus on the details.