December 31: Stability may be better than growth, or it may be an illusion of poor testing
Daily Status, Dec 31
Today is full update
This is the final update for 2020. I am sorry these have become so sporadic, but my own health challenges remain, having had to recover from a nasty bacterial infection which resulted in a nearly 1 week hospitalization, and a pause in my cancer treatments.
Big picture: Like the week after thanksgiving, the number this week (after Christmas) seem to be incomplete. On the surface, numbers appear to be stable – not growing. But, if we look at hospitalizations (which are independent of testing imitations), we see that the numbers hospitalized are at 2570 – about 1000 (50%) more than one month ago. This suggests that actual numbers are probably 50% above where they were in late December; prior to December, we had no days with more than 4000 cases; in December there were 9; At the same time, our precent positive continues to increase, currently at 13..6%, suggesting we are missing more than half of all cases (though that is more likely a problem outside of Northern VA). Hunkering down is the advice of the day. This is a high-risk time period.
The good news is people in Virginia are being vaccinated. It will take a while for everyone to get there, but assuming production can ramp up (big assumption), and more vaccines are approved, perhaps we will have immunity without illness by the summer.
It is really important to remain vigilant. Wearing a mask is like sunscreen. (But without an SPF number). A well fit surgical mask reduced the risk by 80% -- which means if it would take 15 minutes to get a clinically significant dose of COVID, the mask will delay that to about 75 minutes -- you can get sick with a mask but it takes longer. Masks are critical, but not a substitute for being careful. If you are sick -- stay home (except for medical needs).
Not everyone has a strong immune system. This is a societal problem.
Yesterday, VA reported a record 5,239 new cases of COVID-19. Today’s count is significantly (2 standard deviations) above the three-week bias-adjusted average of 3,686 cases.
The current weekly total of 25,669 new cases, or 3667 cases per day, which works out to 43.9 cases/day/100K people. This is in line with observations from the past several weeks The hospitalizations are at an all-time high (2750), which suggests the stable numbers reported a limited by tested. The only good news is we have capacity for 3000 more COVID cases, or about double the current numbers of covid patients in Virginia hospitals, and we will not exceed that for at least a month at current growth rates.
The trends over the last three weeks now are showing an increase at 0.3% per day or 1.7% per week.
Projection for tomorrow: 3553, 90% chance the cases will be between 2615 - 4845
The testing numbers now show the percent positive to be about 2.6x the 5% metric over the last week (13.75%) 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 2.2% of the population in the last week, down from 2.9% in the week prior to thanksgiving. Factoring in the test rates and the percent positive, it would not surprise me to find out we are missing between 50% & 80% of the case
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 risk.
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, though the apparent case counts appear stagnant for the last 4 weeks.
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=1.0025
The following table shows the number per 100K for each region. Again, NOVA Central 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 1000/day per day. (matching the may peak, but with better testing).
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 time constants above 1, we are experiencing exponential growth in the case numbers.
Looking at the trends, the strong downward trend in daily case count we observed since around September 1st has ended. We now see significant jump in cases in every jurisdiction.
The difference in the colors (contrast) in the NOVA map is limited and is warming (as is happening throughout the Commonwealth). At this point, it seems likely that this is related to the fall surge others had predicted. It is worth noting, though, that Vienna/Oakton is doing better than most of the region.
Most localities in NOVA have case counts near or above 25/100K/day. In Vienna, for example, we were under five in late September but are now at 29.2/100K/day. Note that Vienna's numbers are lower than the averages for the Commonwealth, Northern VA and the Fairfax County.
Growth rate (%/day)
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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