Calculating mortality rate mid-pandemic is difficult, but US doesn’t have lowest, experts say

WASHINGTON - As COVID-19 infections continue to climb in nearly 30 U.S. states, while the death toll has surpassed 150,000, a common question among many has been: If someone is infected with the novel coronavirus, how likely is that person to die? 

But accurately calculating the mortality rate of COVID-19 is difficult amid the ongoing pandemic, experts say.

“I’ve always thought that thinking about mortality rates in the middle of a pandemic is incredibly distracting,” said Dr. Ashish Jha, director of the Harvard Global Health Institute. “The reason we don’t care about mortality rate in a snapshot in the middle of a pandemic is it’s very, very hard to calculate.” 

The current U.S. death rate from COVID-19 is below the peak reached in April and early May, but still, daily fatality numbers topped 1,000 over three consecutive days this week, according to the COVID Tracking Project.

President Donald Trump has claimed that the U.S. has “one of the lowest mortality rates in the world.” But experts say a truly accurate global death rate is difficult to know, as every country tests and counts people differently and some nations are unreliable in reporting cases.

“If the question is, do we have one of the lowest mortality rates in the world? No,” Jha said.

John Hopkins University tracks COVID-19 mortality with two measurements: the case fatality rate (CFR) and deaths per 100,000 people in a population — which are both used for different purposes.

COVID-19 case fatality rate

The case fatality rate means that if 10 people have died of COVID-19, and 100 people have been tested and diagnosed with the virus, then the rate is 10%.

Using the case fatality rate, which is simply the number of deaths divided by the number of confirmed cases, the U.S. was ranked #13 when compared to the 20 most affected countries in the world as of July 31.

But this measurement is really just an estimate that is potentially useful for pandemic planning scenarios and does not provide a reliable measurement of actual death rates, according to Dr. Amesh Adalja, a senior scholar at Johns Hopkins Center for Health Security.

“(The case fatality rate) is not definitive and it doesn’t really represent what we would call the IFR, the infection fatality ratio, meaning anybody getting infected, what is their chance of death? And that’s substantially lower,” Adalja said.

The infection fatality rate is the number of deaths from the virus divided by the total number of cases, both tested and untested. For example, if 10 people die of COVID-19, but 500 people actually have it, then the IFR is 10 divided by 500, or just 2%.

The CDC’s current best estimate of the COVID-19 infection fatality rate is 0.65%.

But the problem with these measurements is that many COVID-19 cases go untested, so the true total number of cases is simply not known. And even still, Jha pointed out that outbreaks are rapidly evolving, so the percentage is hard to interpret. 

“For example, imagine that every day out of Florida, 1,000 people are being infected, and 100 people are dying. You’d say, okay, that’s a 10% mortality rate. 100 out of 1,000,” he explained.

“But then imagine that the outbreak starts increasing. A lot of people start getting infected, and you go from 1,000 infected, to 5,000 to 10,000. Deaths are going to take four weeks to show up, because from the day you are infected, people don’t die for about four weeks. So for four weeks, your mortality rate will start going down — because cases are going up, but deaths are not going up,” Jha added. 

So in other words, the larger your outbreak, the better your case fatality rate will look for a long period of time — which is not necessarily a good thing. And the better your testing, the lower your case fatality rate.

“So if we really want to calculate case mortality rate, we have to wait until the pandemic is over,” Jha said.

COVID-19 mortality rate adjusted by population

Another way COVID-19 mortality has been looked at is by adjusting for population, with both confirmed cases and healthy people. In other words, showing how common it is to die of the novel coronavirus within a particular population.

When compared to the other countries most affected by the pandemic, the U.S. has the fourth-highest COVID-19 mortality rate, with 46.48 deaths per 100,000 people in the population, according to a July 31 analysis by Johns Hopkins University.

The United Kingdom has the highest mortality rate with 69.31 deaths per 100,000 people, followed by Peru and Chile. 

“When you look at the number of deaths per 100,000 population, that gives you a more global look at what this virus is doing in any given population,” Adalja said. “It controls for many other factors, including how many (cases) are you picking up? How many are in the hospitals? These numbers of deaths are a little bit easier to kind of compare from place to place, and to understand.” 

So, in other words, is this virus causing more damage in city X or city Y?

Adalja said this method of measurement helps public health experts get a better understanding of what the relative dynamics of the pandemic are in a given area.

“You can also use that to compare this cause of death, coronavirus, to other causes of death by understanding what’s the incidence of coronavirus deaths versus the risk of death from stroke or the risk of death from heart disease,” he added.

Factors that can influence COVID-19 mortality rates

According to experts at Johns Hopkins, mortality rates can be influenced by differences in the number of people being tested.

“We are in a much better place with testing in July than we were in March. We are diagnosing more mild cases, even despite the lag we’re having,” Adalja said. “So that’s going to, in and of itself, bring down the case fatality ratio as we start to recognize more mild cases that are out there.”

Characteristics among the health care system can also have an impact, such as hospitals becoming overwhelmed or having fewer resources, resulting in a higher number of deaths. There also may be improved treatments, potentially keeping more COVID-19 patients alive.

“We’ve learned a lot about this virus. We’ve learned about how to diagnose it quicker, how to treat it better,” Adalja said. “That doesn’t mean this isn’t still a deadly disease and people aren’t going to die from this. However, it does mean that we are getting better and we may see less deaths on an individual case basis, now in July 2020 versus what we may have seen in March or April 2020.”

Demographics also can impact differences in mortality numbers. For example, death rates tend to be higher in older populations.

COVID-19 data reporting issues

Since the onset of the coronavirus outbreak in the U.S., the country has faced reporting issues with critical information needed in the midst of a pandemic.

The Trump administration recently directed hospitals to send coronavirus cases and ICU capacity information directly to the Department of Health and Human Services, bypassing the CDC, as a way to streamline and improve data reporting. But reports have indicated that the new system is plagued with delays and errors.

RELATED: CDC director says his agency was not involved in decision to divert COVID-19 hospital data to HHS

And a report released July 21 highlighted how states across the country are failing to report data necessary to help contain the pandemic.

“It’s a disaster. Six months into the pandemic, we can’t figure out how many people are hospitalized with coronavirus,” Jha said. “We’re not acting like a developed, first world country. This is the kind of stuff that you see in developing countries that don’t have basic computer systems. It is actually quite an embarrassment.”

Jha warned that inaccurate data reporting prevents proper planning in the pandemic, potentially leading to overwhelmed hospitals and ICUs. 

“Hospitals across the country are going to get slammed and are going to be blindsided,” he said. “People are going to die if we’re not able to track this kind of information.”

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This story was reported from Cincinnati.