Ms. Allen’s main goal was to get Ms. McClendon to take her medication regularly to avoid hospitalization.

“The hospital is the dirtiest place there is,” she said. “All the germs are there.”

In California, black adults ages 18 to 39 are hospitalized for preventable asthma problems more than four times as often as white asthma sufferers.

Ms. McClendon, who goes to the emergency room about once a month because of her asthma, conceded that she was “being a bad girl” and not taking her orange inhaler, Flovent, daily. The medication is meant to help keep her airways clear and reduce hospitalizations. She was in the process of getting Medicare but did not go to the doctor for regular checkups.

She promised Ms. Allen to be better about taking the inhaler — for now. A vegan who believes in herbal medicine, Ms. McClendon insisted that once she got her nutrition right, that would be enough to keep her asthma from flaring up. Still, she does worry about the coronavirus, she said. She is using hand sanitizer more and regularly disinfects her car, which she uses to drive for Uber 10 to 12 hours a day, six days a week.

“I know that if I’m not eating right, I’m going to get congested and then I will be a perfect breeding ground for the virus,” she said.

Ms. Blackshear, whom Ms. Allen met later on a sidewalk to administer a nebulizer to help with her coughing and wheezing, had only just started hearing about the coronavirus. While living on the streets, she said, she had little access to news media.

She has heard enough to know to use hand sanitizer a lot. But she does not have the luxury of staying away from people — she needs public transit to get around and sometimes sleeps in homeless encampments. Homeless for the past five years since reporting her former partner for domestic violence, Ms. Blackshear said she had not been able to work because of her asthma and mental health and substance abuse problems.