Data Update

Massachusetts Data Update October 3, 2020

My data updates tend to be very table oriented. I find this a useful way to present information that can be easily and quickly grasped. But that approach can obscure longer term trends that provide context about the spread of Covid in Massachusetts. This data update provides graphical formulations of selected data from my usual coverage to better illustrate where we are compared to where we’ve been.

I’m starting these graphs on June 1st for two reasons. First, some of the information I present has only been published in the daily coronavirus updates provided by the Commonwealth since June 1st. Second, the scale of certain data prior to June 1st is so out-sized relative to current information that it obscures recent trends in the data. As an example, the number of reported hospitalizations peaked at almost 4,000 in late April, compared to 300 to 400 today. When a graph is scaled to include 4,000 hospitalizations, changes from 300 to 400 appear small. Relative to the beginnings of the outbreak, that change is indeed small, but in the current context that change may be significant.

Figure 1 shows test positivity rates through October 1st. The black line is the positivity rate for newly tested individuals. This is the rate the state emphasized through mid-August, when it switched its headline positivity number to the “all test” positivity number (shown in red). The black “new individuals” line clearly shows a decline in test positivity during June, shows that positivity rates were under control (under 2%) during July and August, and shows that rates began to increase near the end of August. As of the October 3rd update, this rate has climbed to 3.6%.

The blue line is the positivity rate for repeat testers. It demonstrates the changing composition of repeat testers over time. Through mid-July, repeat testers were likely individuals who had tested positive for coronavirus and were getting retested to see if they were clear. At that time, the positivity rates for repeat testers were higher than the rates for those newly tested. Starting sometime near the end of July, it appears that preventative testing (for front-line workers and college communities) became more prevalent among repeat testers, driving down the repeat testing positivity rate below the rate for newly tested individuals. It has been about 0.2% for several weeks.

We can also derive the mix of new testers and repeat testers. The “all test” line is a weighted average of the “new individuals” line and the “repeat tests” line. In June, the “all test” line is closer to the “new individuals” line, indicating that more of the tests were for new individuals (roughly a 75-25% mix). Over time, especially as the amount of college testing has increased dramatically, the “all test” line has moved closer to the “repeat tests” line (now roughly 75-25% but with the categories switched).

Figure 2 summarizes hospitalization information, also through October 1st. For clarity, the number of patients hospitalized (in black) is shown on the right axis, and the other statistics (ICU patients, intubated patients, and new admissions) or shown on the left axis. The scale ratio between the two axes is 4:1.

Hospitalization and ICU figures track each other well, with a relatively steep decline until the end of July, a roughly level period until around Labor Day, and a gradual increase since. It is a bit difficult to tell from the chart because hospitalized patients and ICU patients are shown on different scales, but the percentage of patients in the ICU has declined from about 25% at the beginning of June to about 20% now (although the percentage bottomed under 15% near the end of July).

The number of intubated patients as a percentage of ICU patients declined from about 70% at the beginning of June to about 35% currently. While intubations have increased slightly since Labor Day, the increase is smaller in percentage terms than the increase in the number of ICU patients, either because admitted patients are less ill than previously, or because treatment protocols have changed. The ratio of new admissions to total hospitalizations has been relatively constant since June 1 – between 4% and 7% until just about a week ago, when it went above 7% for the first time. That is perhaps a worrying trend.

Figure 3 shows the 7 day trailing average number of cases and deaths. Cases are shown in black on the right hand axis, deaths are in red and blue on the left hand axis. The scaling is 10:1.

As Figure 3 illustrates, the daily number of deaths declined rapidly through June and the beginning of July, but has been basically steady since then. The same is roughly true for deaths in long-term care facilities (LTC Deaths). About 70% of all (confirmed and suspected) deaths since June 1 have been in long-term care facilities. This ratio has been declining over the past month, but very slowly.

The number of cases also dropped sharply through the end of June (with a low under 200 cases per day), but began to tick upward starting in July, leveled off during much of August, and then started its current sharp upward swing after Labor Day. Much of the recent increase is not from increased testing, but from higher positivity rates among those newly tested. Testing has increased from about 9,000 new individuals per day at the end of June to about 15,000 per day now (and peaked at about 20,000 near the end of August), but the newly tested positivity rate was already below 2% on June 30, compared to 3.6% today.

3 replies on “Massachusetts Data Update October 3, 2020”

Well done. An interesting aspect of testing that you may want to look into is the false positive rate. Google BMJ sensitivity specificity calculator. As prevalence goes down and rate of testing rises (i.e screening), the rate of false positives invariably rises. For example, a test with a 95% sensitivity and a prevalence of 5% yields a false positive rate of 50%.

Does anyone know if there were any events like last Saturday, like thousands of people pouring into the street to celebrate something that could have led to the recent spike we are seeing this week????? Seriously, can anyone think of ANYTHING at all?????

The spike started well before the celebrations last Saturday. For example, last Saturday the state reported 2,038 new confirmed cases and 75 suspected cases before any celebrations started, and 2200 confirmed/107 suspected on Sunday, well before anyone would have had test results back.

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