Nov 30: Lower testing numbers through the holiday means lower reported cases, but not fewer infections.
Daily Status, Nov 30
Today is a full update
The data are impacted thanks to the Thanksgiving holiday.
Big picture: There is an apparent pause in the case growth. This is probably a direct result of fewer test results being reported during the 4 days before the weekend compared with the 4 day weekend (2776/day vs 2234/day). This is probably a result of statistically fewer tests conducted over the holiday weekend. In all probability we will not return to background activity for several days. Expectations are holiday travel and gathering will result in an increase in cases though we will not know for certain until around 12/10.
Yesterday, VA reported 2,228 new cases of COVID-19. Our fall surge has paused for at least one week, but I expect this is more a result of reduced holiday testing than case reduction. If that is the case, numbers will surge in the next several days (such a possible surge is not factored in my numeric estimates). Today’s count is in line with the three-week bias-adjusted average of 2,317 cases.
The current weekly total of 16,481 new cases, or 2,354 cases per day, which works out to 28.2 cases/day/100K people. This number is down slightly from last week. But the hospitalizations are at an all time high, suggesting that the decrease is more a reduction of mild cases not being tested than an actual drop in case infected people. We are now above early May peak(currently 1569; peak was 1727). Since hospitalizations should not be impacted by testing levels that provides a strong indication that the caseload is now probably similar to that in May. Though, in May, the cases were concentrated in in NOVA, whereas now, the distribution is more uniform throughout the Commonwealth. If we look at hospitalizations, we had 2x the number of hospitalizations in May in NOVA than we do today.
The trends over the last three weeks now are showing an increase at 2.7% per day or 20% per week.
By combining our current regional trends with the typical reporting for the day of the week, I expect about 2,549 cases tomorrow (Friday) with a 90% chance of the numbers falling between 1,874 to 3,470 cases.
The testing numbers now show the percent positive to be above the 5% metric over the last week (8.36%) which is often used to indicate sufficient testing. This is concerning because, as the percent positive increases, it is possible that some cases are being missed as the number of positives is constrained by the testing availability. VA is tested about 1.8% of of the population in the last week, down from 2.9% in the prior week, suggesting we are missing several hundred cases per day.
When we look at the local ZIP code data, we see that the observed increases are almost universal across VA. I am comparing the current estimated % positive to that of one month ago. Note that almost all is a warmer color (further from blue and closer to yellow). This is an indication of the uniformity of the increase. As a practical matter, it means to be safe and careful, no matter where in VA you live, there is 2-3x the risk as there was around 10/1.
In the spring, COVID-19 in VA was primarily a concern in the DC suburbs. Over three to four weeks, (from late May to early June), NOVA recovered and for about a month the disease was under control to the point that restrictions were eased. Unfortunately, in eastern VA/Hampton Roads, the easing of restrictions resulted in a surge in cases which peaked just before August 1st resulting in stricter restrictions in that area. Since then, with the exception of growth on college campuses, the disease has been stable, excluding the rural parts of the state where safeguards (social distancing and masks) are largely ignored. Starting in October our weekly case count has been increasing throughout the Commonwealth, particularly in NOVA and SWVA, and NWVA
Looking at the weekly case count, we see that the numbers are higher than at any other point in the pandemic.
Regional growth rates (in fraction per day) continue to show degradation over the past three weeks. Note: It is easier to show a decline when the prior numbers increased. The current growth rates for the different regions are shown below.
The entire state is increasing with Rt=1.027
The following table shows the number per 100K for each region. Again, NOVA and Eastern VA are doing the best, and the mountainous regions in NW & SW continue having more cases. The concerning aspect is that in all regions the numbers for last week are significantly higher than the preceding three weeks. What is most concerning is that SW & NW VA are hitting significantly higher caseloads.
The following charts show all five regions of the Commonwealth over time.
The individual line charts show the unfiltered data per day, coupled with the trend lines.
The trend lines show the different periods of growth.
Early in the pandemic, the different parts of VA were functioning largely independently, with NOVA mimicking the northern states, and Hampton Roads mimicking the southern states. Since September 1, the regions have trended together. Starting in late September, NoVA and SWVA diverged from the rest of the state, a trend that continues today.
Currently SWVA has the greatest number of cases even though they have half the population of NOVA.
Note that the effects at both ends of the chart are probably artifacts of the (seven-day polynomial filtering I use for averaging); the filter is poorly constrained in the first and last few days of the time history. For those technically inclined, the filter is called a Savitzky-Golay filter, basically a moving window polynomial filter. At the edge (first and last days of the time series), the filter will over-compensate for the trend as it is unconstrained. I recommend the Wikipedia article if anyone is interested in more information, or contact me.
After the early peak in May (~1,000 cases per day), NOVA saw a sharp drop in all COVID metrics, reaching a broad valley in mid-June (~200 cases/day), which lasted until around August 1st. By Sept 1, NOVA increased to 300 but the caseload dropped to about 150 by late in the month. Since then we have had a steady increase averaging up to a current value of 725/day per day.
City of Alexandria
Prince William Co.
The number above is Rt: Rt is an exponential time constant, where the number of cases in a time segment is approximately, n=Ao Rt ^ t, where Ao is the number of cases at the start of the segment, Rt is the exponential growth rate, and t is the number of days since the start of the segment. So, if Rt is greater than 1, it is growing exponentially, if it is less than one, it is decreasing each day.
Another way to look at it, todays number are approximately the growth rate times yesterday's numbers. This is the exponential time constant. with constants above 1 and case counts 20/100,000 per day, we are teetering on being really bad. Ideally, we would be 0, we are still better than our early May peak was around 30/100000K; we should exceed this within a month.
The difference in the colors (contrast) in the NOVA map is increasing. In addition, the NOVA map is warming (as is happening throughout the Commonwealth). We had been in the blues to greens, now we are in the greens to yellows. At this point, it seems likely that this is related to the fall surge others had predicted.
Most localities in NOVA have case counts near or above 10/100K/day. In Vienna, for example, we were under five in late September but are now at 22.2/100K/day.
Growth rate (%/day)
In Vienna, the average daily case count has doubled; I do not why (I have not been out and about). However, I suspect the cause is primarily people locally and state wide tiring of the pandemic.
I am not updating this section for the time being except for the charts. I will leave it here as is for a while longer--at times it can be very interesting. This is particularly so when specific age groups do not follow other groups. For example, teens and 20-somethings surged in early September while the other age groups did not due to the outbreaks at colleges.
Given that most colleges are shutting down for the semester in the next week, the report on colleges will be on hiatus.
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