Editor's Note: Kent Sepkowitz is a CNN medical analyst and infection control expert at Memorial Sloan Kettering Cancer Center in New York. The opinions expressed in this comment are yours. See more opinion at CNNe.com/opinion.
(CNN) - An interesting moment in Fox News journalist Chris Wallace's memorable interview with United States President Donald Trump was a confusing round-trip of covid-19-related deaths. The president claimed that the United States had the "lowest death rate" in the world, while Wallace insisted that the country had little to boast about.
Although it is clear that Trump is completely wrong, comparing the impact of the covid-19 pandemic looking at the mortality of each affected country turns out to be a very complicated matter. Because no metric is perfect, especially when used to compare impact across countries, there is a large epidemiology corner devoted to how to more accurately tabulate death.
The Centers for Disease Control and Prevention (CDC) devotes a long chapter to addressing the best metric for a given situation in the course, "Principles of Epidemiology in Public Health Practice."
As covid-19 reports have evolved, the death count has been the most cited number to track the size of the tragedy in the U.S. and other countries. According to John Hopkins University, more than 148,000 human lives have been lost in the US due to this disease.
A lot of time could, and should, be spent understanding the death count, especially as a growing proportion of the US, now 31%, thinks the count is an overestimate. In contrast, most public health experts feel strongly that there is an underestimation.
The simple death count is not used to compare with other countries, due to the large differences in the population size of each nation. To account for this variation, most public health experts prefer to use rates, not counts.
The two most popular rate measures are the case fatality rate (CFR) and the total population rate (with and without the disease), called the death rate. The Johns Hopkins Coronavirus Resource Center, which Chris Wallace and Fox News cited during the Trump interview, offers users an easy switch between the two measures.
The case fatality rate measures the number of deaths divided by the number of people diagnosed with the disease. The advantage of this metric is that it is intuitive, and it is exactly what a person with covid-19 wants to know: given the diagnosis, what is the probability that she will die? The downside is substantial, because the rate can change depending on the amount of the population that is tested for a disease.
As an example, think of a country with 100 inhabitants, where four people are hospitalized with covid-19 and six others are diagnosed but are well enough to stay home. If a contact or community trace is not performed, only 10 people are known to have the infection. Three of these 10 die, producing a case fatality rate of 30%.
Now, consider that that same country, with that same population of 10 infected people, conducted a contact screening and community testing, diagnosing 10 additional inhabitants with mild or no symptoms. As in the first example, three people die, but here the case fatality rate is 15% (three deaths in 20 known cases). In other words, more testing leads to a lower CFR, a point that could make the president a test fanatic.
To avoid the big problem introduced by the number of diagnostic tests, the mortality rate, on the contrary, uses the total population (those with the disease, diagnosed or not, and those without the disease). All the world. Point.
This metric is of little value to a patient who wants to know their prognosis but measures exactly what public health authorities need to know: how bad is this in my country compared to others. Using the example above for the country of 100 inhabitants with three deaths from covid-19, the death rate would be 3%, regardless of how many people were tested.
The Johns Hopkins data used by many media outlets, including CNN and others, present a table with information on the 20 countries most affected by covid-19. During the interview, Wallace showed case fatality rates (although he called them death rates) and correctly stated that the United States is seventh (now tenth) among these 20 countries, far from the "lowest" in the world.
Something worse? From the way Kayleigh McEnany quickly produced the charts at the President's request, it appears that the information used by the White House in the interview could also be used in decision-making.
Their statistics are obtained from another (non-US) source: Our World in Data, compiled by the University of Oxford in the UK. These data use CFRs and, unfortunately for those who expect the President to see the truth without a filter, it allows anyone to select as many or as few countries as they like to frame the crisis according to their specific goals.
Although it is difficult to discern in the video of the interview (at approximately 2:45), President Trump used a graph that included information about only seven countries. In this group, the United States ranked fourth (in my opinion) with a worse death rate than Iceland, Brazil, and South Korea. Once again, even with carefully selected data from the White House, the United States is mediocre at best.
An even more sobering view of how the US is doing is our actual death rate per 100,000 people (not fatality rate). Using this metric from Johns Hopkins data, the US has the 17th worst mortality rate of the 20 worst affected countries.
The number or rate of covid-19 deaths in the United States is a disaster, regardless of the metric used. And it is clear from the interview that President Trump willingly presents erroneous information given to him, even while the cameras are on.
But perhaps the most disturbing aspect of watching the interview is that it strongly suggests that the data being given to the President is deliberately incomplete.
Apparently, he is informed how the United States classifies according to the case fatality rate compared to six other countries using a metric that public health experts consider below the death rate.
It seems that every step of the way, those charged with presenting the truth to the President have chosen to voluntarily protect their own well-being over that of the people of the United States.
