As measles spreads across the country, sick children and adults are exposing other patients — including newborn babies — when they seek care at hospitals, pediatrician’s offices and urgent care centers.

To help control the spread of measles, one of the world’s most contagious viruses, medical experts say people with suspected cases should take precautions before visiting a doctor’s office or the emergency room.

“I never want to discourage anyone from seeking care,” said Dr. Alison Haddock, president of the American College of Emergency Physicians. But “measles is highly contagious and it is dangerous to expose others.”

Walking into a crowded clinic or emergency department, especially without a mask, can infect others in the waiting room, including patients who are pregnant, medically vulnerable or immunocompromised, said Dr. Ari Brown, a pediatrician in Austin, Texas, and spokeswoman for the American Academy of Pediatrics. An unvaccinated child with measles, who had been infected while traveling abroad, sparked an outbreak in San Diego in 2008 that included children in the waiting room of a pediatrician’s office.

“If you have any concerns” about being infected with measles, “do not just show up at the pediatrician’s office. Do not just show up at the ER,” Brown said. “Call first so they can be prepared.”

As of Friday, the U.S. has seen upward of 500 measles cases in at least 20 states and Washington, D.C. since the beginning of the year. The majority are in Texas, where an outbreak on the western edge of the state has grown to 400 cases and spilled into New Mexico and Oklahoma. Two people have died, including a 6-year-old girl.

While anyone who is unvaccinated can be infected with measles, patients in hospitals and clinics may be especially vulnerable to complications, especially if they are pregnant, immunocompromised or in fragile health, Brown said. The measles virus can survive in the air for two hours after an infected person leaves the room, according to the Centers for Disease Control and Prevention.

Dr. William Schaffner, an infectious disease expert at Vanderbilt University Medical Center, suggested alerting ER staff that someone with measles is on their way.

Schaffner also advised people to bring a second adult to the ER along with the sick patient. While one adult waits outside the building with the sick patient, the second adult should go inside, notify the ER staff and find out what precautions to take before bringing a potentially infected patient inside.

ER staff may need time to prepare an isolation room for someone with measles. These rooms have specialized airflow and filtration systems to prevent airborne viruses from drifting into public areas, Haddock said.

Given the overcrowding in most ERs, however, “staff may need to rearrange patients to make this room available to you,” Haddock said.

Measles patients and their family members or caregivers should wear masks when in any health care facility, Haddock said. ER staff may ask people with measles to enter through a special door, such as the ambulance bay, to reduce the risk of exposing other patients.

Few primary care practices have isolation rooms, also known as negative air pressure rooms, Brown said.

Doctors may prefer to see people with suspected measles cases by telehealth. Other doctors may choose to see patients in the parking lot — a common practice during the Covid pandemic, Brown said. Alternatively, doctors may see patients with suspected measles infections at the end of the day, after other patients have left the clinic.

Even mild cases of measles can make people feel miserable.

“It’s not just a normal fever and a rash,” said Dr. Paul Offit, director of the Vaccine Education Center at Children’s Hospital of Philadelphia. “These kids are sick.”

About 20% of people who get the measles are hospitalized. In children, the most common causes of hospitalization are pneumonia or dehydration, caused by diarrhea, Offit said.

There’s no specific treatment for measles, Offit said, other than supportive care, such as fluids and fever-reducing medications. Antibiotics don’t help a measles infection because it’s caused by a virus, although doctors may prescribe antibiotics for children who develop secondary bacterial infections. Doctors recommend that children get a lot of rest. Children may feel better in a dark room, because measles can make them sensitive to light.

Although many children with the measles can be safely treated at home, parents should call a doctor if their child appears short of breath or dehydrated, Offit said. It’s easy for children with fevers to become dehydrated, especially if they have diarrhea and aren’t able to drink enough fluids.

Offit, who has treated many measles patients, said he has diagnosed the illness on the basis of symptoms — including a fever, cough, runny nose, pink eye, sensitivity to light and white spots on the inside of the mouth. Many younger doctors have never seen the measles, however, and may miss the diagnosis. Doctors can make a definitive diagnosis with a blood test or by swabbing a patients’ nose or throat. It can take several days to get results back from a hospital or public health lab.

Brown notes that many people don’t realize they have measles and may believe they have a bad case of the flu. That’s because the characteristic red measles rash doesn’t show up for four days after symptoms start. The rash follows a pattern, beginning on the face at the hairline and gradually spreading down the body. People are contagious for four days before the rash appears and four days after; patients should stay home during this time to avoid infecting others.

Because measles has a long incubation time, unvaccinated people can reduce their risk of measles by getting a vaccine within 72 hours of exposure, Offit said. Measles vaccines are extremely effective, with two doses preventing 97% of infections.