Wednesday, April 15, 2020

Projecting Deaths from COVID-19 (an update)

On April 2, I published a blog (here) analyzing available information to put in context the 100,000–240,000 U.S. deaths then being projected. More recently, the government has reduced projections to 60,000[i]. That’s a sizeable difference. What’s up?

The modification from the initial range resulted from two major components: how many would become infected in the U.S. and what percentage of those affected would die. Dr. Fauci, in announcing the reduction to 60,000 projected deaths, suggested the decrease came about because much of the country embraced the shelter-in-place and social distancing.

Flattening the Curve

In the previous blog, I compared the U.S. response to controlling the novel coronavirus to the efforts of Italy, Germany and Spain[ii]. Because of Germany’s massive early testing, the slope of their infection growth is the lowest. Spain is worst because they continued to allow massive public gatherings for a longer period than the other countries. Italy, which experienced infections earlier, was in the middle. The U.S., which experienced large numbers of infected two weeks after Italy and one week after Spain and Germany, continues to follow a path close to Italy, but slightly worse.

Covid-19 reported cases per million

We’ve lost our opportunity to be like the Germans. Our infection rate per million population has already exceeded theirs, even though we are a week earlier in the curve. We are doing much better than Spain. The U.S. still has the potential to bend its curve so it will not experience the same infection levels as Italy.

One piece of (comparative) good news is that for several days the number of new cases in the U.S. has decreased from its worst day. This peak occurred a week earlier in the curve than the peak happened for Italy, suggesting our social distancing has helped. The tail, however, is long.

Italy’s worst day was March 21 when they reported 6,557 new cases. That gave them 53,578 total infected. Yesterday (April 14), their cases stood at 162,488. That means more that twice as many people were reported infected in Italy after their worst day than before it. Yesterday, Italy reported nearly 3,000 new cases. Their tail continues to lengthen.

German’s worst day was March 22 with 6,933 new cases. That gave them 57,695 total infected. Yesterday they stood at 132,210. With a significantly flatter curve than Italy, they experience a multiplying effect of 1.3 cases after the peak for every pre-peak case.

Spain reached their high a few days later. On March 26 they reported 8,271 new cases, totaling 57,786. Their total yesterday was 174,060. Matching Italy, they had more than twice as many people infected after their peak than before it.

The U.S. experienced its highest reported cases on April 4, with 34,196. At that date we had 311,413 total cases. Yesterday we had reached 613,886 (nearly double) with 26,945 new cases that day. We are not experiencing Germany’s tapering; we continue to track Italy’s experience. If that remains the case, we can expect another 300,000 infected in April, bringing us to over 900,000 by the end of the month.

What’s happening with death rates?

In the previous blog, I suggested a method to estimate the death rates of reported cases: take total deaths and divide by reported cases a week earlier. Excluding China (because of their likely under-reporting of deaths), I estimated on April 2 a ratio of 12.8%.

Updating that calculation to April 14, yields 123,259 total worldwide deaths (excluding China). Total reported infected on April 7 (excluding China) were 1,352,655. The ratio is 9.11%. This decline is welcome news. I suspect the reasons for the decline combines wider testing catching many more “light” cases and possibly better treatment.

Where are individual countries right now? Using total reported deaths and infections (not adjusting for the week delay between report and death), Italy’s death rate is currently 13.0% (up from 12.1% on April 2); Spain has reached 10.5% (up from 9.2% on April 2), and the U.S. has climbed to 4.4% from 2.5% on April 2.

Unfortunately for the U.S. our rate of testing (9,260 per million population) is well below the three comparison countries (Spain - 12,833; Germany - 15,730, Italy - 17,758). Iceland is the world-leader with 106,490 per million of population! Given that our current testing protocols[iii] are designed specifically to exclude those most likely to recover (not too sick, not elderly or otherwise at risk), our death rate is unlikely to be much better than the world at large. I will change that assessment as a larger percentage of cases derive from countries with inadequate hospital facilities (India, Turkey, and most African countries are still in the early part of the infection curve). Their future inclusion will, I fear, drive up the worldwide death rate. For now, however, their effect on the overall rate is minor.

Applying the current 9.11% rate to the projected 900,000 U.S. cases through April yields 82,000 deaths.

Given the experience of other countries, there is no reason to expect that Covid-19 infections will magically stop on May 1. A percentage of those later infections will also die. Perhaps the original 100,000 will prove accurate after the counting is complete.

I hope Dr. Fauci’s estimate is correct, and mine is overstated. My overstatement could arise from two areas.

The U.S. does not follow Italy’s trend line and develops fewer than the 900,000 cases I projected before May 1. This will be great news—unless the reason for the decline is a continued inability to test all the people we should.

The U.S. death rate proves to be lower than the current worldwide estimate. This could arise because the U.S. health system finds more effective treatments than were available to other countries. We can hope for this great blessing. We also could experience a lower death rate because we accelerate testing and catch more infected patients earlier, thereby allowing healthcare to provide better care. Sadly, testing has not increased. As illustrated in the chart prepared by the CDC and available on their website[iv], despite promises, the U.S. rate of tests done in April are only slightly higher than those performed at the end of March.

CDC Covid-19 Lab Tests

I have my fingers crossed that I am wrong.

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