SALT LAKE CITY — As COVID-19 cases continue to climb in the United States, public health experts and care providers are seeing more clearly what factors lead to severe disease and who the novel coronavirus kills.

Recent national conversation includes some crowing that deaths seem to be decreasing, even as case numbers rise. That isn’t apt to be borne out by science, health experts warn. It’s more complicated than comparing today’s infection count with today’s death count, since death trails infection by weeks or even a month. A death surge may still be coming.

The “best estimate” from the Centers for Disease Control and Prevention is that 0.4% of people who actually show symptoms die, but it notes a range from 0.2% to 1.0%.

“There’s still a lot that we don’t know,” said Andrew Noymer, associate professor of public health at the University of California Irvine, because it takes years to figure out a disease.

COVID-19 and the SARS-CoV-2 virus that causes it are newcomers, unheard of less than a year ago. That leaves a lot to figure out, from how many people are infected to what factors lead to more severe disease, how various ages are impacted and what portion of those who are infected will die.

What’s in a number?

There are multiple ways to measure COVID-19 deaths, according to Rebecca Ward, a health educator in the Utah Department of Health’s Bureau of Epidemiology. Experts use variations — and different terminology.

Among common measures:

The mortality rate per 1,000 cases divides the number of deaths by the number of cases, then multiplies it by 1,000 so the result is simple to read. This number reflects the rate of death due to COVID-19 among those who have the illness.

The mortality rate per 100,000 population divides the number of deaths by the overall population, sick or well, and then multiplies that number by 100,000 to make it easy to read. This number indicates the rate of death from COVID-19 in the total population.

The case fatality rate divides the number of deaths by the number of cases to yield a percentage. In a make-believe scenario, if 1,000 people have a virus one year and 20 of them die, you divide 20/1000, which comes out to a 2% case fatality that year.

The COVID-19 death rate has been tricky to untangle. People don’t all use the same terms. Most people actually wonder: How many of those who are infected with COVID-19 will die? That is answered in the case fatality rate, which is found by dividing the number of deaths within a period of time by the number of known infections in that period.

It’s a hard number to calculate because actual infection numbers are elusive and death takes time.

Clouded hope

Some good reasons exist to believe the seeming decline in the case fatality rate might be real, since doctors know more about caring for COVID-19 patients and are saving some who might have died earlier. More people — and a broader range of people — have been tested, including more young people, who are less likely to die. When tests were scarcer, only those with symptoms and known risk factors were tested.

Dr. Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases, told the JAMA Network that at its peak in spring, the United States had 30,000 cases daily, with 2,500 deaths. It’s now up to 50,000 cases each day, but only about 500 deaths. He said that besides the age of those tested, another factor might be that we are protecting old adults in nursing homes and the community better.

But Noymer points out that as long as case numbers are rising, the case fatality rate stays low because the denominator, which is the number of infections, is constantly expanding. The deaths lag. People dying today were among infections reported weeks to a month ago — and deaths resulting from new infections can only be accounted for in the future.

“The way the death-to-case ratio keeps dropping — it’s like a Ponzi scheme,” Noymer told the Deseret News, “because cases keep growing before the deaths have time to catch up.”

Calculating risk

While the virus hasn’t changed, its toll is not consistent from place to place. Older adults are generally more likely to die of COVID-19 than younger ones, so the age of those infected in a community changes the result. Obesity’s a risk factor, as are diabetes and heart or lung disease, among others. How many among those infected have such underlying conditions makes a difference, and that could vary drastically from place to place. There are racial differences in rates, so some communities see more deaths based on their diversity.

In addition, the quality and availability of medical care matters. There are even differences in urban vs. rural communities, some as basic as what care is available nearby or how far one must travel to get it. Whether the person filling out the death certificate lists COVID-19 or pneumonia can change whether a death is counted. The list is long.

The CDC just updated the underlying conditions that pose the greatest risk of severe illness and death. They are cardiovascular disease, chronic kidney disease, chronic obstructive pulmonary disease, obesity, immunosuppressing condition or treatment, sickle cell disease, receiving an organ transplant and type 2 diabetes. The more conditions one has, the greater the likelihood of severe illness, Dr. Robert Redfield, CDC director, said in a media briefing.

A patient is wheeled out of the Cobble Hill Health Center by emergency medical workers in the Brooklyn borough of New York on Friday, April 17, 2020. | John Minchillo, Associated Press

Conditions that could complicate infection include lung diseases like asthma and cystic fibrosis, high blood pressure, a weak immune system, neurologic conditions, liver disease and pregnancy, Redfield said.

Noymer said some deaths associated with COVID-19 probably won’t make official counts, like a guy with diabetes who didn’t get treatment during the pandemic and died.

CDC assessment released July 10 on Americans who died between Feb. 12 and May 18 — close to 1.3 million confirmed cases and 83,000 related deaths — found most were older than 65 and had underlying medical conditions. CDC said a third were Hispanic. The rate of non-whites younger than 65 who died was about three times that of whites in that age group. When the CDC looked at those for whom it had more detailed information, three-fourths who died were 65 or older.

CDC monthly situation reports, using Johns Hopkins University Data

The median age for non-whites who died was a decade younger than whites’ median age of 81.

United Kingdom study looked at data on more than 10,926 who died from COVID-19 or complications. The researchers said people ages 80 and older were 20 times more likely to die of COVID-19 than infected people in their 50s — and 100 times more likely than those younger than 40.

Besides medical conditions and race, risk factors include poverty and being male. The Deseret News reported men might be more susceptible due to more ACE 2 receptors, which is how the virus enters the body.

Figuring out why

Dr. Dagmar Vitek, medical director of the Salt Lake County Health Department, said local public health sees much the same pattern, with those most at risk of severe illness or death being people who are older and those with chronic medical issues. She noted higher rates in the Hispanic population, which is why her department established hotspot areas to improve access to testing and services, including in Rose Park and West Valley City.

Vitek suggested the higher infection rates in those communities might arise from people working in industries like construction or restaurants where work can’t be done remotely. Some extended families may also live together.

Some experts say we’re asking the wrong questions. “... This really is about who still has to leave their home to work, who has to leave a crowded apartment, get on crowded transport, and go to a crowded workplace, and we just haven’t acknowledged that those of us who have the privilege of continuing to work from our homes aren’t facing those risks,” Harvard’s Dr. Mary Bassett told The New York Times.

Utah scores well on having fewer health risk factors and on state life expectancy rankings, Noymer said.

Still, the case rate in Utah has been steadily rising since June, said Rebecca Ward, health educator in the Utah Department of Health’s Bureau of Epidemiology. The mortality rate among infected people has dropped some, but the share of COVID-19 deaths among the general population has increased some in the past couple of weeks.

“So we’re seeing a lower mortality rate in terms of the increasing number of cases, but not really in terms of the overall population,” she said.

“It is important to keep in mind that even if a case doesn’t have a severe outcome themselves, they can still transmit the disease to someone who may be more at risk,” she said.