People struggling with drug addiction are particularly at risk of contracting coronavirus — because many have underlying health conditions, compromised immune systems and are vulnerable to relapse because support group meetings in some areas have been canceled, experts say.

Homeless, those sleeping in crowded shelters or people with other health conditions — such as hepatitis C, HIV or lung disease — are high risk, said Dr. Daniel Solomon, an infectious disease physician who works at the Brigham Health Bridge Clinic for patients with substance use disorders.

“We know they are particularly vulnerable,” he said. “What can be disruptive to us can be devastating to them.”

The clinic has been giving patients longer prescriptions and converting as many appointments as possible to phone calls, Solomon said, but some can’t afford phones.

For recovering addicts, anxiety about COVID-19 can have a “triggering effect” that can lead to relapse, said James McKowen, a psychologist and clinical director of the Addiction Recovery Management Service at Massachusetts General Hospital, which is moving toward treatment via telemedicine, phone calls and group-based video conferencing to reduce the risk of transmission.

“The problem with that is lots of folks don’t have computers or housing,” McKowen said.

Another concern is that some Narcotics Anonymous meetings, “which can be the backbone of someone’s recovery,” he said, have been suspended or moved online. But many addicts can’t afford computers, leaving them at risk of being alone, without the structure and support they need, McKowen said.

“So much of the work we do is working with patients on a frequent basis,” said Vanessa Ryan, a nurse practitioner at the South End Community Health Center, “but we’re going to have to temporarily discontinue group counseling.”

Anthony Andreottola, director of the Father Mychal Judge Recovery Center at St. Anthony’s Shrine, a church in Downtown Crossing that has closed until March 21, said he will have to counsel people by phone.

“It’s been challenging because people have to change the way they receive help,” Andreottola said. “People are nervous. They feel isolated. And many of the people we serve don’t have the luxury of staying at home. You can’t wash your hands if you don’t have a sink. So the first thing I’m telling everyone is you don’t want to compound any problems you might have with a relapse.”

The Addiction Treatment Center of New England in Brighton offers addicts recovery coaching, sponsorship in 12-step programs and a network of other people in recovery, layers of support that are more “imperative” than ever, said Matthew Donlan, the center’s CEO and a recovering addict who has been clean for 16 years.

The outpatient center also offers daily doses of methadone, suboxone or Vivitrol, the three most common medications used to treat opioid use disorder. That has been unaffected by the state of emergency Gov. Charlie Baker declared on Tuesday, Donlan said.

“If the state or federal government told us we needed to, we could give people a certain amount of medication to take home with them, but it’s not something we’d prefer to do if it can be avoided,” he said. “We’re going to ride it out and help as many people as we can.”

In most cases, even people with the most means, however, have not been able to be tested for coronavirus, said Dr. Alysse Wurcel, an infectious diseases physician at Tufts Medical Center.

“The best thing we can do is reconsider the judgments we make when we walk by someone who’s homeless and struggling with addiction,” Wurcel said, “and heighten our level of compassion.”