© Photograph by STR/AFP/China OUT via Getty Images Doctors look at a lung CT image in a hospital in Yunmeng County, Xiaogan City, in China's central Hubei Province.

High blood pressure, diabetes, and cardiovascular disease are so commonplace that everyone reading these words likely knows somebody with at least one of these maladies.

They are also the “underlying conditions” most associated with severe cases of COVID-19, based on early clinical profiles on the disease. Even though 80 percent of COVID-19 cases are mild, these reports reveal that the novel coronavirus can endanger people other than the elderly and infirm.

The idea that the virus only poses a threat to older people comes from focusing too heavily on COVID-19’s death rate, which the World Health Organization updated last Wednesday to 3.4 percent. This rate is an average across ages, and the chances of dying do rise among older people.

But evidence also shows that COVID-19 is more fatal across all age groups than seasonal influenza, with death rates six to 10 times higher for those under 50. Moreover, death isn’t the only danger, and severe cases of COVID-19 are more common among young adults than you might think.

A study published February 28 in the New England Journal of Medicine, for example, examined the age breakdown for 1,099 coronavirus patients. The majority of non-severe cases—60 percent—are teens and adults between 15 to 49 years old, which might suggest this group is spared the worst of the virus.

In truth, severe cases were slightly more abundant among this younger demographic. Of the 163 severe cases reported in the study, 41 percent were young adults, 31 percent were aged 50 to 64, and 27 percent were above 65. The only age group spared by severe COVID-19 appeared to be kids under 14.

Millennials and Gen Z are also just as likely to catch the coronavirus as older groups, according to the largest profile to date on COVID-19, a clinical report of more than 72,000 patients published February 21 by the Chinese Center for Disease Control and Prevention. So rather than rely on age to gauge who is most threatened by COVID-19, doctors say you may want to look at common underlying conditions and how they correspond with the death rates reported by the Chinese CDC. Doing so can offer clues on how to protect you and your loved ones.

“The death rate from this outbreak is high. We shouldn’t categorize it by young or senior,” Tedros Adhanom Ghebreyesus, director-general of the World Health Organization, said during a Monday briefing. “We cannot say that we care about millions when we don’t care about an individual who may be senior or junior … Every individual life matters.”

Cardiovascular complications

The novel coronavirus tears apart the lungs, but the underlying condition most connected with COVID-19’s worst outcomes are afflictions of the heart.

Nearly half the adults living in the United States have high blood pressure. Likewise, diabetes is a household name, with one of every 10 Americans—34.2 million across all ages—dealing with the metabolic disorder. Both can factor into cardiovascular disease, a wide spectrum of disorders that kill one person roughly every 37 seconds in the United States.

Though the specific influence of COVID-19 on the cardiovascular system remains unclear, the American College of Cardiology states, “there have been reports of acute cardiac injury, arrhythmias, hypotension, tachycardia, and a high proportion of concomitant cardiovascular disease in infected individuals, particularly those who require more intensive care.” One study of 150 patients from Wuhan, China—the epicenter of the coronavirus outbreak—found that patients with cardiovascular diseases had a significantly increased risk of death when they are infected.

That’s because the heart and lungs are incredibly interconnected. Breathe in and out rapidly, and your pulse automatically increases its pace. But if your heart is already weak or you have blocked arteries, then you are working harder than a normal person to circulate blood and oxygen throughout your body.

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“If this new virus enters our communities as it has been, I really worry for my cardiac patients,” says Erin Michos, a cardiologist and director of Women's Cardiovascular Health at Johns Hopkins Medicine in Baltimore. “During their day-to-day existence, their heart is having trouble pumping efficiently, and then you add a serious respiratory infection on top of that. That's the tipping point.”

Cardiac distress is yet another arena where the coronavirus mirrors what happens with the flu. Influenza has long been established as a propellant for heart attacks and cardiovascular disease, so much so that some doctors have wondered if the seasonal virus is a direct cause. A 2018 study published in the New England Journal of Medicine found that within seven days of a flu diagnosis, people were six times more likely to have a heart attack.

“I don't think the community fully appreciates it,” Michos says. “We know that viruses can trigger a heart attack or stroke.”

Moreover, people can be infected by more than one disease at the same time, further exacerbating any existing heart conditions. In a preliminary study of coronavirus patients from Wuhan, four percent of confirmed cases were infected with a second virus, mostly influenza.

“If your immune system is weakened already ‘cause you're fighting off one major pathogen, you're much more susceptible to get a secondary infection,” Michos says.

That’s why she, the U.S. Centers for Disease Control and Prevention, and the American Heart Association recommend that cardiac patients take extra precautions as the coronavirus outbreak grows, which includes getting vaccinated for the flu and bacterial pneumonia.

Underlying pressure

When it comes to matters of the heart, many people may also be at risk from underlying conditions they don’t even know they have. For example, high blood pressure—or hypertension—contributes to atherosclerosis, a process whereby the walls of a person’s blood vessels grow dense plaques made of fat and tissue fibers. If one of these plaques erodes or ruptures, it can block the blood vessel, leading to a heart attack or stroke.

Michos says a lot of people are walking around unaware with plaques and hypertension. The CDC estimates that 108 million Americans have hypertension, but at least 11 million have no idea.

That’s where the threat of respiratory infections such as influenza and coronavirus comes in. These infections can create a “blood storm” of inflammation that courses throughout a person’s body. (Once your body's infected, this is what coronavirus does.) An early study of Wuhan patients spotted “fulminant myocarditis,” an unusual syndrome that erodes the muscles in the heart.

“We know, especially for people who have no history of cardiovascular disease, that inflammation can be a trigger for a plaque rupture,” Michos says. Diabetes can also spur atherosclerosis and accelerate these plaque ruptures, and those with the disease also have relatively suppressed immune systems, making them more vulnerable for infections.

Given we are in the midst of flu season and the coronavirus crisis, Michos recommends that cardiac patients and diabetics make sure that they have enough of their regular medications, and that everyone checks that their blood pressure is under control.

Asthma action plan

Beyond cardiac health, the coronavirus outbreak has serious implications for people with chronic respiratory illnesses such as cystic fibrosis, chronic obstructive pulmonary disease, asthma, or allergies, as well as for people with lung damage linked to smoking. Even mild cases of a cold or the flu can aggravate these conditions, increasing one’s chances of landing in the hospital.

One alarming distinction with COVID-19 is the long incubation period before symptoms appear, which ranges from two to 14 days. Another is the six-weeks-and-counting delay in America’s rollout of a coronavirus test, due to a technical error made by the CDC. Both contribute to a situation in which members of the general public can be infected and contagious, yet have no awareness of their illness. And a new study published Monday in Lancet found that coronavirus patients shed the virus, an indicator of being contagious, for between eight to 37 days.

“I would advise anyone with a chronic respiratory illness before they travel, especially using public transportation, that they sit down and come up with a plan of protection,” says Enid Neptune, a pulmonologist at Johns Hopkins Medicine. Such a plan could be as simple as upping dosages of routine medications, or as thorough as pinpointing which nearby hospitals employ respiratory specialists.

“That may also mean not going to certain parties or gatherings where you don't really know where people have been or what their health status is,” Neptune says. Most of all, patients should not shy away from seeking professional advice.

“Sometimes patients feel that they're being alarmist and are inappropriately notifying their physicians,” Neptune says. “When there's a great deal of misinformation in the public arena and when there's much that we don't know yet about the virus, this is the time to use your medical contacts.”

Cancer containment

Cancer patients are also in the group that needs to be concerned about respiratory conditions. People being treated with intensive therapy for leukemia or lymphoma, and those receiving bone marrow transplants, are among those more prone to catching pneumonias, including the viral versions. That’s because their immune systems are often compromised as a result of their tumors or due to the treatments they receive.

“Patients who have had cancer treatment in the past may also remain immunologically compromised even though they appear to have recovered,” says J. Leonard Lichtenfeld, deputy chief medical officer for the American Cancer Society in Atlanta.

These cancer patients are sometimes so jeopardized that they cannot take vaccinations and must rely on the protection afforded by community-wide immunization. For now, the sole intervention for vulnerable cancer patients is social distancing and enhanced hygiene practices for their family and health care workers.

“That's difficult, because obviously cancer patients are at different stages of their illness, and people want to be with their loved ones,” Lichtenfeld says. “But we're all in this together, and we need to all take appropriate steps to protect ourselves and protect those we love.”

The kids are alright?

At the same time, all the data collected so far suggest that COVID-19 is rare and less severe in children. Through February 11, the Chinese CDC recorded 44,600 confirmed cases, but only 400 involved kids under 9 years old, and none died. So does this mean children are less likely to be infected, or that they just don't get very sick?

“All of us in the field think the latter is true,” says John Williams, chief of the division of pediatric infectious diseases at the University of Pittsburgh Medical Center. Early tracing among close contacts and in households has found that children are just as likely to catch the novel coronavirus as adults. The low number of childhood cases reported so far could be due to testing being concentrated at hospitals, Williams notes. “Once testing involves more mild patients, outpatients in clinics, and doctor’s offices, you will find more adults and probably a lot more kids.”

Seeing fewer kids with severe COVID-19 has some precedence among other coronaviruses and infectious diseases. Pediatric cases occurred during the SARS coronavirus epidemic 20 years ago, but most were mild. And while chickenpox is occasionally fatal for kids, unvaccinated adults who catch the disease are much more likely to suffer severe pneumonia and end up in the hospital.

“For any infectious disease, part of the symptoms and damage are caused by the germ itself, while part is caused by our immune system responding to the infection,” Williams says. “So the thought is that perhaps children, because their immune systems are less mature, just don't mount as much of a response to the infection as adults do.”

Despite this youth benefit, the school closures seen worldwide are justified, because children are the major spreaders of every respiratory illness known to exist. In the U.S., about 20 percent of American children get infected with the flu every year, versus 5 percent of adults.

“We also have a lot of vulnerable children in this country with chronic conditions,” Williams says, such as transplant recipients, cancer chemotherapy patients, or children with chronic heart and lung diseases. “We don't know yet if those kids are going to be at higher risk for more severe COVID-19 disease, but based on other viruses, my guess would be yes.”