(CNN) While there's concern for the elderly catching coronavirus, there's another high-risk group that has nothing to do with age.

People with underlying medical conditions are also more likely to become seriously ill if they get it.

Some of them are young and most of them may not look sick at all. Millions of them are living with a compromised immune system.

It's estimated that about 3% of the adult US population is immunosuppressed, according to a 2013 National Health Interview Survey . That's roughly 7 million people living with a weakened immune system today.

Some of them have a disease that's weakened their immune systems. Others are taking immunosuppressants for cancer or organ transplants.

Coronavirus has made life a lot harder for the immune-compromised. These are some of the challenges they're facing:

There are days when Brittania Powell can't get out of bed.

They may not look sick, but they have an invisible disease

Brittania Powell is a college student with a bright smile and a love for the food of her native Jamaica. She goes to class and works at a caterer, but what many don't know is that she's dealing with several conditions they can't see.

On a good day, Powell can walk to class at Columbus State Community College in Ohio. On a bad day, she can't bend her knee enough to walk.

She can wake up to any joint in her body being swollen and inflamed and she can't predict when it'll happen, she said.

Powell was diagnosed with the autoimmune disease lupus when she was 14. She also has rheumatoid arthritis , anemia and lupus nephritis, which inflames her kidneys.

"Lupus and other immune-compromised diseases, a lot of them are invisible diseases," Powell said. "I realize that it's hard for people to take it seriously, acknowledge it or even think about it on a daily basis if they can't see it."

Powell wants people to know that just because she looks healthy, that doesn't mean she is. She hasn't left her place in more than 10 days because she wants to avoid getting coronavirus.

"There are people out there that may look completely healthy and bright, but on the inside, we're struggling," she said.

Powell hopes that people take "others into consideration," she said. Do little things, such as washing your hands and coughing into your sleeve, that make a big difference for someone who's immune-compromised.

Danielle Grijalva is self-isolating to protect herself from getting sick.

Self-isolating is a struggle that's not new them

When flu and cold season comes around, some people with weakened immune systems go into self-isolation mode, like Danielle Grijalva.

That practice started when the mother of two woke up not being able to walk one day in 2015. She lost her career and the old life she knew.

The 44-year-old Californian became homebound and wasn't able to walk, drive or do the things she needed to do, she said. It took three years until she had the diagnosis of a pain condition called fibromyalgia , chronic fatigue syndrome and several strains of echoviruses, which were found in her stomach.

"I know how much that that lack of independence sucks," Grijalva said. "But for us that are immune compromised, that's something that we deal with all the time."

Healthy people are just getting used to isolating themselves at home as coronavirus spreads. For Grijalva, it's always been a measure to protect herself.

"Now they're kind of understanding what we have to deal with on almost a daily basis," she said. "It's not that we're germophobes. It's not that we are wanting to be introverts and stay home and be home bodies. It's that we have to do this in order for us to not to get so deathly sick."

Andrew and Emily Linder got hitched a month before she gave him a kidney.

Sometimes they have to isolate even from loved ones

We're living in an unprecedented time that's full of uncertainty. People everywhere are huddled at home with their spouses and families, but for some, even that's too risky.

Newlyweds Andrew and Emily Linder are living in separate homes because Emily doesn't want to get her husband sick. He will be on immunosuppressants for the rest of his life because he had an organ transplant.

The couple made the heartbreaking decision for Emily to move in with her parents 45 minutes away. She left earlier this week.

Both of them are licensed counselors. Andrew, 32, is starting telehealth sessions from home with some of his patients. His wife works with the homeless and people in the prison system, so there's a much higher risk that she could bring home an illness such as coronavirus.

"It's probably one of the hardest decisions of my life," Andrew told CNN from his home in Akron, Ohio. "The woman who literally saved my life gave me a kidney. There's no other act I can ever think of that just shows that much love to me."

Linder was in stage 3 kidney failure when he met his wife-to-be.

After he was unable to find a donor, Andrew's friends and family were tested. By the "graces of higher power," his girlfriend was a perfect match.

The couple has spent a lot of time crying this week, but they are texting and video calling each other a lot. The virtual connection is no substitute for being there.

"It's not the same as waking up next to your partner," he said. "This is not how we want to start our marriage."

Eileen Davidson is always washing her hands. That goes for her son Jacob, too.

It's hard when others aren't considerate

Getting coronavirus is scary. People disobeying health and safety guidelines during this pandemic are just as frightening.

After Eileen Davidson explained why she was self-isolating, an acquaintance who had recently been at the airport licked his finger and touched her shoulder. That disregard for social distancing put Davidson at risk.

The 34-year-old is a single mother with an autoimmune disease called rheumatoid arthritis. She lives with her 7-year-old son Jacob in Vancouver, British Columbia.

"It's just people making a joke over it because they don't realize the actual severity of all this," Davidson said. "I'm more afraid of other peoples' complete disregard for others and stupidity than the virus at times."

Even death has been the butt of a few coronavirus jokes. Phrases like "boomer remover" and "culling the herd," referring to the elderly, sick and disabled, make Davidson angry when she reads them.

It's been hard for anyone to get hand sanitizer, Lysol spray and disinfectant wipes at local stores. People like Davidson rely on those products to stay germ-free and keep her children safe, too.

Some people have been waiting to get essential supplies until they receive their disability or retirement pay, the freelance writer and patient advocate said.

"I would really love for people to be considerate of others when it comes to emergency supplies," Davidson said.

She supports the select stores that have implemented special hours for the elderly and vulnerable to shop and avoid being around crowds.

Courtney Hodge is a single mom to 19-year-old Austin.

Getting coronavirus could be fatal

Courtney Hodge is religious about cleaning everything she's touched because anything could affect her diminished respiratory function.

The 37-year-old has asthma and several autoimmune disorders such as Graves' disease , fibromyalgia and chronic fatigue syndrome . She gets sick easily, she said.

"It's being hypervigilant over everything that I touch because you don't know who else has touched it," Hodge said.

Where has her purse been? Maybe it's time to Lysol it. Is it worth handling cash? A card would be safer. These are just some of her thoughts.

"I have to constantly be vigilant because I can't let anything take me down," Hodge told CNN. "Something like Covid, it would kill me. It's not like it would just make me bedridden, it has the potential to kill me."

Coronavirus causes fever, cough and difficulty breathing . With how suppressed her immune system is, Hodge worries she wouldn't be able to fight off the damage coronavirus does to someone's lungs.

"Best case scenario, I get it and it gives me, like, really bad respiratory problems," Hodge said. "I would be in the hospital for who knows how long, and I may never fully recover from it."

Her biggest motivation to stay healthy is her son, Austin. He came home to the Pittsburgh area after his university encouraged students to move out.

"To put in now 19 years of hard work to make sure that he's a decent human being and he's smart ... and then to know that that could be taken away from me is just -- it breaks my heart."

Correction: A previous version of this story misstated the number of Americans with a weakened immune system. It is roughly 7 million, not 9 million. This story has also been updated to clarify that the figure refers to Americans 18 and older.