Just after physicians in Wuhan, China, began reporting new, potentially fatal respiratory disease COVID-19, scientists and officials assured the world that most cases were mild and that the most serious cases occurred in patients with underlying conditions.
The Centers for Disease Control and Prevention’s Weekly Morbidity and Mortality Report released on March 31 corroborated the claim. While the CDC reports 60 percent of adults in the U.S. have a chronic condition, it estimated that 78 percent of patients admitted to the intensive care unit with COVID-19 between Feb. 12 and March 28 had at least one. But of those diagnosed with COVID-19 who weren’t hospitalized, only 27 percent had an underlying condition.
The novel coronavirus SARS-CoV-2, which causes the disease COVID-19, typically enters the body through droplets inhaled into the nose or mouth. From there, these virus-laden drops can go on to infect cells in the airways and lungs as they travel deeper into the respiratory system. In the worst cases, the infection damages the lungs so severely that patients can’t breathe on their own and can die.
Predictably, having a preexisting condition that affects the same organs that the virus attacks is linked to more severe illness. While 13.4 percent of the population reports having a chronic lung condition, 21 percent of COVID-19 patients admitted to the ICU had one.
But patients with two other conditions were even more likely to be admitted to the ICU: those with diabetes (32 percent of COVID-19 patients in the ICU) and cardiovascular illnesses (29 percent of patients). Even patients who survive after their hospital stay are likely to experience complications like organ damage and hospital-acquired infections that require further treatment. Some may suffer from post-traumatic stress disorder or other mental illnesses after leaving the ICU.
These and other conditions seemingly unrelated to the lungs, like chronic kidney disease, chronic liver disease and neurological impairment, all increased the likelihood that a patient with COVID-19 went to the ICU — or, worse, died from the disease.
COVID-19 and Cardiovascular Disease
Epidemiology data from China published near the end of February showed that over 10 percent of COVID-19 patients with cardiovascular conditions died — the highest rate of fatalities among common underlying conditions — compared with 2.3 percent of the entire population of patients.
For infectious disease experts like Peter Gulick, a physician and researcher at Michigan State University, and heart disease experts like Eduardo Sanchez, chief medical officer for prevention with the American Heart Association, this is not surprising. The two explained that patients with heart conditions are especially susceptible to complications from respiratory infections — like influenza, SARS and MERS — because of the way serious infections strain the heart.
Normally, oxygen flows into the lungs, through the blood stream and into the heart. But when lungs are badly infected, less oxygen can make it past that first step, and the heart won’t have enough to pump throughout the body. This causes “incredible stress on the heart” as it works harder and harder to make up for the lack of oxygen, says Gulick. “And then it causes people to have heart attacks and heart failure.”
Our body’s attempt to fight the virus can wreak havoc on the heart as well. Once the immune system recognizes an invader, white blood cells rush into battle to rid it from the body, causing widespread inflammation responsible for symptoms like fevers and muscle aches.
“The inflammatory process happens, to some degree, inside of muscle, including heart muscle,” says Sanchez. In some cases, this causes myocarditis — inflammation of the heart muscle that can be serious enough to cause irregular heartbeats and heart failure. Inflammation can even loosen plaques in the blood stream, freeing them to flow toward the heart and cause a heart attack.
The American Heart Association recently directed $2.5 million to scientists researching the heart and brain effects of COVID-19 in hopes of better understanding these complications and any long-lasting impacts.
COVID-19 and Diabetes
Though patients with cardiovascular disease were the least likely to survive the infection, COVID-19 patients taken to the ICU had diabetes more often than any other underlying condition. Both diseases are similarly prevalent, each affecting a little over 10 percent of the general population.
There are two main ways diabetes can contribute to worsening outcomes. The first is that the condition can weaken the immune system — especially if the patient’s blood sugar levels are not well controlled — making it more difficult for the body to fight off the infection. “The virus has the ability to perhaps do more than it might in a person who does not have diabetes,” says Sanchez.
The second is that the infection can make it more difficult for patients to continuously control their blood sugar. “Stress on different areas of the body can cause the blood sugars to get out of control and actually worsen the diabetes,” says Gulick.
Direct Infection by SARS-CoV-2
Lastly, emerging evidence suggests SARS-CoV-2 may be able to infect and damage organs outside of the respiratory system.
Viruses can’t replicate on their own, so once they enter the body, they must invade our cells and use them to replicate. In the case of SARS-CoV-2, the virus can only enter cells that have a particular receptor on the outside, called ACE2, which is prevalent in the respiratory system. This is what allows the virus to take hold in our airways when it first enters the body.
But this receptor is also found in the heart, intestines, kidneys and liver, suggesting that if the virus travels far enough to encounter these organs, it may be able to infect them as well.
“It's not common,” says Gulick, “but [researchers] have reported cases where the virus may directly cause infection of the heart itself.” Some research suggests that the virus may be able to infect and damage the kidneys and other organs. Patients have reported gastrointestinal symptoms and even neurological complications like confusion.
Moreover, many patients with an underlying condition have more than just one. Diabetes is often connected with heart disease, liver disease and kidney disease. For example, “kidney disease is a disease multiplier,” says Joseph Vassalotti, chief medical officer of the National Kidney Foundation and a nephrologist at the Icahn School of Medicine at Mount Sinai. “A person with kidney disease often doesn’t have only kidney disease.” All of these can make it harder for a patient to fight off the disease.
According to data from China published in JAMA, about 2.3 percent of patients with a lab-confirmed diagnosis of COVID-19 will die. But that number rises dramatically for patients with underlying conditions. The fatality rates were 10.5 percent for patients with cardiovascular disease, 7.3 percent for those with diabetes, 6.3 percent for those chronic respiratory disease, 6 percent for those with hypertension, and 5.6 percent for those with cancer.
Still, Gulick emphasizes that all people, even younger patients and those without underlying conditions, need to be cautious. “They still have a high mortality rate,” he says. “They shouldn’t take it too lightly.”