The coronavirus outbreak has turned many of us into nervous germophobes, seeking to protect ourselves from infection by washing our hands methodically and frequently, avoiding unnecessary contact with so called high-touch surfaces and methodically sanitizing packages, our homes and our bodies.

For people diagnosed with obsessive-compulsive disorder, or O.C.D., the worry created by the threat of coronavirus has the potential for more intense and longer-lasting implications.

According to the International OCD Foundation, there are about three million Americans who have been diagnosed with O.C.D. It’s a condition characterized by unwanted thoughts or urges that generate high levels of anxiety and repetitive acts meant to neutralize the obsessional thought.

The cleaning and sanitizing practices that help prevent coronavirus infection are bringing people with O.C.D. into closer orbit to behaviors that are a gateway to detrimental patterns that could interfere with their ability to engage meaningfully with the world outside their homes for years to come.

Courtenay Patlin, a 28-year-old in Los Angeles, is trying to find balance between appropriate caution and overreaction. Several weeks ago, before the California shelter-in-place order, Ms. Patlin decided to mostly stay indoors.

She had read enough about how quickly coronavirus had spread in China, Italy and then Seattle, and how very sick it was making so many. She felt she could rely on only herself and her Clorox to stay healthy.

“I keep a very clean apartment, and I feel safe at home,” she said.

Ms. Patlin, a graduate student studying clinical psychology, was diagnosed with O.C.D. about five years ago, she said, after years of being afraid of public toilets, refusing to eat off dishes that she hadn’t scrubbed herself or witnessed being sufficiently cleaned by others and being fearful of being hugged by basically anyone.

She used to clean her apartment and her hands with pure bleach and cleaning solutions until the skin on her fingers started to peel off, which she would take as a sign that she was cleaning the proper amount.

In recent years, she said, she had managed what is known as “contamination O.C.D.” with medication and therapy. But these days, Ms. Patlin has felt her O.C.D. take reign again.

When she heard a neighbor sneeze across the courtyard, she closed her windows to keep out any shared air. When a friend picked up Ms. Patlin’s prescriptions from a pharmacy and left them for her at her doorstep, she wiped down the bottles with bleach, in the hope of killing any germs the pharmacist may have transmitted.

The most complicated part is she doesn’t even know anymore what’s too much.

“These are the moments when I am asking myself, ‘Is that my O.C.D. or should I be doing that?’” Ms. Patlin said. “The lines are getting blurred.”

The lines between O.C.D. and avoiding dangerous germs today

About one-third of people with O.C.D. are afflicted by contamination O.C.D. The new reality of a pandemic that requires acute attention to the transmission of germs creates additional peril for these people.

“The rules have changed,” said Julia Hitch, a psychologist in Seattle whose practice is in part devoted to treating children and adults with O.C.D.

“Friends and neighbors are now engaging in O.C.D.-type behaviors, and it’s making people in treatment with O.C.D. wonder: ‘How do I not let this get out of hand, and what is out of hand anymore?’” Dr. Hitch said.

Those who have successfully gone through treatment to overcome or manage a contamination obsession and sanitizing compulsion are working hard to cope.

Bella Ronan, a 19-year-old in Kirkland, Wash., was diagnosed with O.C.D. when she was 9. Her symptoms began, she said, after her younger sister, Frannie, was born. Ms. Ronan obsessively worried about germs coming into the house that could harm her sister, who has Down syndrome.

To avoid transferring germs from one room to another, Ms. Ronan designated a different pair of slippers for each room of the house. She would change her slippers three times as she went from the kitchen to the living room to the laundry room. If her mother wiped down a table with a cleaner that had chemicals in it and Ms. Ronan’s book was placed on the table, she would refuse to touch the book again for fear of being contaminated by the chemical.

“I was washing my hands 40 times a day, scrubbing them so they were raw and bloody,” said Ms. Ronan, who is living with her family while on a gap year between high school and college.

Years of intensive therapy and finding the right combination of medications offered short-term relief from the O.C.D., she said. But her life was changed after she turned 18 and was eligible for an adult residential treatment program.

She stayed for eight weeks and the treatment consisted of intense exposure therapy during which Ms. Ronan tested her fears that germs and chemicals could make her sick by touching various surfaces and liquids (for example, the bottom of shoes, bathroom countertops and laundry detergent) and then gradually extending the amounts of time before she could wash her hands.

The residential treatment was followed by a monthlong step-down recovery program, during which she lived in an apartment with other O.C.D. patients.

“The only way to overcome the O.C.D. is to learn to live with it, and that’s by living an exposure lifestyle,” Ms. Ronan said.

Now, she is focused on staying healthy mentally and physically. “I’ve spent almost 11 years having something inside my head tell me things that would cause my mom, my dad, my friends and my therapist to say, ‘That’s a little extreme.’” she said. “But now those same people are telling me to wash my hands all the time so I don’t get sick, and I’m trying to wrap my head around it all.”

Ms. Ronan has asthma, which makes contracting Covid-19 even scarier. She is taking her cues on sanitizing from her mother and father, who she trusts.

“If they say I should wash my hand for 20 seconds under warm water, I know there are facts causing them to tell me to do that and I’m relying on facts,” she said. She is also listening to advice from doctors and other experts she hears on TV or reads about in news articles.

Becky Ronan, Bella’s mother, is struggling with her own anxiety connected to her older daughter’s condition. “As worried as I am about anyone getting Covid-19, I’m equally worried about her having a backslide and having to go back into a residential program,” Becky said. “That is just as scary as Covid-19.”

Therapy and O.C.D. in the time of coronavirus

Exposure and response prevention therapy is the most effective treatment, experts say. It systematically tests a patient’s worries that something will harm them by exposing them in a prolonged, repetitive and intensifying system to things that they fear.

When the exposure doesn’t cause significant illness or harm, the patients can begin to learn how to better cope.

But the unusual and urgent focus on sanitation to fight the spread of the virus is also creating concerns for health care professionals involved in the treatment of O.C.D., said Bradley Riemann, a psychologist and the chief clinical officer of Rogers Behavioral Health, which has mental health and addiction treatment centers around the country. (Dr. Riemann is also the clinical director of Rogers’s O.C.D. Center, in Oconomowoc, Wis.)

That’s why providing treatment for O.C.D. right now is especially complicated. “This is clearly a time when we have had to change the way we interact with one another and the way we interact with our environment — it’s a matter of public safety for all of us,” Dr. Riemann said. “But it really collides with the world of O.C.D., and in particular with patients with contamination O.C.D.”

Usually, Dr. Riemann and his staff work with patients by asking them to interact with germs, increasingly extending the amounts of time between washing their hands or otherwise sanitizing. In some situations, he said, patients are asked to touch toilet seats or bathroom floors, and then are given food to eat before washing their hands.

“As you can see, the world we live in today, that collides head on with that kind of treatment intervention,” he said. “It has been very challenging to try to achieve a balance where you are keeping your staff and patients as safe as we all can be, yet still providing effective treatment.”

Dr. Riemann said he and other professionals in this field have been conferring daily about ways to dilute exposure therapy so that it conforms to the public health coronavirus standards while still offering therapeutic value.

So far this has meant having patients wash their hands before eating, because that is a coronavirus necessity, and then touching an item that creates trepidation in the patient but is unlikely to carry the virus, like a pillow from their own home, for example.

Managing O.C.D. today

Connor Kelly-Eiding, 31, was diagnosed with O.C.D. earlier this year, and the coronavirus crisis has made the symptoms feel more acute. Ms. Kelly-Eiding, an actress who also works for a women’s rights advocacy organization by helping to connect survivors of sex abuse with law firms, has been leaving her apartment with her boyfriend only to go running, and even that is a challenge.

“If we see other people, I become consumed with how we are going to maneuver around them and I begin to see a cloud of germs surrounding them that I will have to run through,” said Ms. Kelly-Eiding, who lives in Los Angeles. “I understand intellectually that some of my fears are not based in fact, but many of them are, actually.”

She reached out in February to a local O.C.D. association, and last week she began phone therapy to address her fear of germs. “I’m so grateful that there is help out there,” she said.

A silver lining for some people diagnosed with O.C.D. is that the pandemic is showing them how far they have come.

Jeffrey Blitt, 21, a junior at Tufts University in Massachusetts, was studying abroad in Brisbane, Australia, when he and his fellow students were ordered to return home in March. The logistical complications of having to get from one side of the world back to his family home in New Providence, N.J., distracted him from focusing on any fears of germs.

When he was 11 years old, such fears dominated his thoughts so completely that he was not able to go to school and was sent by his parents to Rogers for residential treatment.

Since arriving home from Australia, however, even as the grip of the virus has grown more intense, he is taking note of how much progress he has made.

“At a certain point in time this would have been some of my worst fears realized,” Mr. Blitt said. “But my O.C.D. anxiety is almost completely under control. It’s almost weird seeing everyone do the things I used to do, like people watching hand-washing videos and my mom leaving packages outside,” he said.

(His mother, Lisa Blitt, who was in the same room as her son as he spoke on speaker phone, interjected in her own defense, “It’s safety versus O.C.D.,” she said. “Better safe than sorry.”)

Mr. Blitt, who has always relied on humor to help him cope — as a kid he once dressed as a bottle of Purell for Halloween — is still finding ways to laugh.

“More than anything I see a dark humor in it,” he said of the ritual hand washing and germ worrying being embraced by his relatives and friends. “‘I think to myself, ‘Oh, I was doing all those things and I’m passed it and now everyone is doing it.’”