Dr. Scott Isaacs has worked as an endocrinologist for more than two decades, focused on the medical needs of adults with diabetes in the Atlanta area. He never expected to be serving on the front lines of a pandemic.

For weeks, his phone has been ringing off the hook. His diabetes patients, a high-risk group for coronavirus infection, want to know: How can they get tested? How can they stockpile extra medication? And can he write to their employers to recommend they work from home?

Last week, Dr. Isaacs saw a patient with Type 1 diabetes, a nurse who is 10 weeks pregnant. She asked him how long she should stay home from work to avoid possible exposure, and he had to respond honestly: “I really don’t have an answer to that.”

Dr. Isaacs is used to relying on his medical expertise, but the coronavirus has suddenly put him in new territory, an experience shared by many medical specialists who may serve as the primary physicians of patients with particular medical needs. Physicians across every field who are trained to care for very specific medical problems are confronting a surge of patient questions and scrambling to keep up with rapid changes in case numbers and advisories from governments and health agencies.