What Are ‘Comorbidities,’ Anyway?

Rochelle Walensky, the CDC director, recently said it was “encouraging news” that most people who have died of COVID-19 had multiple comorbidities. While I’d disagree with the “encouraging” part, I think it’s important to take a look at what comorbidities really are.

What does comorbidity even mean?

Morbidity is a word that refers to illnesses and health conditions. It’s the counterpart to mortality, which means death.

So why don’t we just say that? Well, these are general words that statisticians and public health people use when they’re analysing large pools of data. (Fun fact: the CDC’s public health journal is called the MMWR, for Morbidity and Mortality Weekly Report.)

Comorbidity, then, refers to having multiple morbidities, or health conditions, at once. If somebody who died of COVID has “four comorbidities,” that means they had four other health conditions, besides COVID.

Which comorbidities raise the risk of dying of COVID?

So what counts as a comorbidity? Depends who you ask. When Walensky made her infamous quote, she was referring to this report (from, yes, the MMWR). So let’s look at how that paper breaks down the comorbidities.

First, they weren’t looking at every possible comorbidity. Instead, they had a list of eight conditions that they considered to be risk factors:

Risk factors for severe outcomes included age ≥65 years, immunosuppressed, and six other underlying conditions. All persons with severe outcomes had at least one risk factor; 78% of persons who died had at least four.

The term “risk factors” is more accurate than “comorbidities,” since being 65 years old isn’t an illness. The list of risk factors from the paper includes these:

• Age 65 and older
• Immunosuppressed
• Chronic pulmonary (lung) disease
• Chronic liver disease
• Chronic kidney disease
• Chronic neurologic (brain) disease
• Diabetes
• Chronic cardiac (heart) disease

For more information on which health conditions increase your risk of death or severe disease from COVID, the CDC has a more complete list here. For example, they include Alzheimer’s and dementia under neurologic disease.

These risk factors are fairly common, and commonly occur together. For example, 17% of adults over 65 have a heart condition and 27% have diabetes. We probably all have at least a few neighbours and family members who have four of the risk factors on the list.

That’s why it’s not encouraging that, as Walensky said, “the overwhelming number of deaths, over 75 per cent, occurred in people who had at least four comorbidities.” Yeah, it would be worse if COVID were targeting healthy people at the same rate as those with comorbidities, but if you’re breathing a sigh of relief at this news, you’re probably forgetting that many Americans have these conditions, including some of your loved ones.