Put aside age: Underlying health plays a big role. In China, 40% of people who required critical care had other chronic health problems. And there, deaths were highest among people who had heart disease, diabetes or chronic lung diseases before they got COVID-19.
Preexisting health problems also can increase risk of infection, such as people who have weak immune systems including from cancer treatment.
Other countries now are seeing how pre-pandemic health plays a role, and more such threats are likely to be discovered. Italy reported that of the first nine people younger than 40 who died of COVID-19, seven were confirmed to have "grave pathologies" such as heart disease.
The more health problems, the worse they fare. Italy also reports about half of people who died with COVID-19 had three or more underlying conditions, while just 2% of deaths were in people with no preexisting ailments.
Heart disease is a very broad term, but so far it looks like those most at risk have significant cardiovascular diseases such as congestive heart failure or severely stiffened and clogged arteries, said Dr. Trish Perl, infectious disease chief at UT Southwestern Medical Center.
Any sort of infection tends to make diabetes harder to control, but it's not clear why diabetics appear to be at particular risk with COVID-19.
Risks in the less healthy may have something to do with how they hold up if their immune systems overreact to the virus. Patients who die often seemed to have been improving after a week or so only to suddenly deteriorate — experiencing organ-damaging inflammation.
As for preexisting lung problems, "this is really happening in people who have less lung capacity," Perl said, because of diseases such as COPD—chronic obstructive pulmonary disease—or cystic fibrosis.
Asthma also is on the worry list. No one really knows about the risk from very mild asthma, although even routine respiratory infections often leave patients using their inhalers more often and they'll need monitoring with COVID-19, she said. What about a prior bout of pneumonia? Unless it was severe enough to put you on a ventilator, that alone shouldn't have caused any significant lingering damage, she said.