Beyond the Sheer Numbers

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This has been a week in which hospitals in New York and many other states began to be overwhelmed by the exponential growth of coronavirus cases. When every patient counts and every death is a tragedy, the sheer number of cases is daunting.

Having said that, epidemiologists have to look at rates and growth trends as well as sheer numbers to understand an epidemic, and so do the rest of us. In last week’s post, I used the concept of doubling time to compare mortality trends in different countries, based on data from Our World in Data. The good news this week is that the doubling times in days are increasing a little in most countries, meaning that the rate at which deaths are multiplying is slowing. The bad news is that exponential growth curves are still very steep in many places. Deaths are doubling every four days in the United States and United Kingdom, apparently the fastest growth in the world. The doubling times are five days for Germany, six days for France and Netherlands, seven days for Spain, and ten days for Italy.

To appreciate the implications, if Italy’s deaths would keep doubling every 10 days for the next 30 days, its 15,362 deaths would double three times, increasing by a factor of 8 to 122,896. But if US mortality would keep doubling every 4 days in the same period, its 8,501 deaths would double at least 7 times, increasing by a factor of 128 to 1,088,128. To put that in perspective, 405,000 Americans died fighting World War II. No one knows what the real numbers will be, since no one knows how much and how fast we can bend the growth curve. What is clear is that the United States is poised to become the world leader in coronavirus deaths very soon. How the country that prides itself on the world’s most advanced health care system could accomplish that feat is a topic for another time.

State mortality rates

Within the United States, death rates also provide additional perspective to raw numbers. As of this morning, the ten states with the highest number of deaths are New York, New Jersey, Michigan, Louisiana, Washington, California, Illinois, Massachusetts, Georgia, and Florida, based on data from the Washington Post. Taking into account state size by using deaths per 100,000 population changes the picture somewhat. California’s 289 deaths no longer look so large, and Vermont’s 20 deaths become more significant. California’s rate of less than 1 death per 100,000 drops it down to 30th in death rate, while Vermont’s 3 per 100,000 brings it up to 7th. Illinois, Georgia and Florida also drop out of the top ten, to be replaced by Connecticut, Colorado and the District of Columbia. The number of deaths in a small state may get less attention, but it can have a large proportional impact on the smaller number of medical personnel and hospital beds.

Not only do states differ greatly in total deaths and death rates per 100,000 to date, they are also adding deaths at very different rates. Most of the states with the most deaths—either raw numbers or deaths per 100,000—have also had relatively large percentage increases over the past week. Increases of 300% or more are common—New York’s is 331%—but Michigan and New Jersey have seen increases over 500%. One notable exception is Washington, which has the sixth highest death rate so far, but one of the slower rates of weekly growth, 67%. The virus hit Washington first, but stay-at-home measures seem to be working. California has both a low rate of death and a below-average rate of weekly increase, having been the first state to issue a stay-at-home order.

Meanwhile, other states have had relatively low numbers and rates of death so far, but now have above-average rates of growth. Tennessee’s mortality rate is less than 1 per 100,000, but its deaths increased from 7 to 50 in a week, an increase of 614%. Other states that experienced significant jumps from low beginnings were Alabama, Kentucky and Maryland.

Given the potential for exponential growth to change the situation with dizzying speed, current low numbers are no excuse for complacency, anywhere in the country.

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