Infectious Disease Specialists (also known as ID doctors) treat both acute and chronic infections caused by bacteria, parasites, fungi and viruses. These may be infections caused by hepatitis, HIV, COVID-19, tick, mosquito or parasite infections, and infections of unknown origin. There are several subspecialty areas that an infectious disease physician can train in: HIV/AIDS, Tropical Medicine, Hepatitis, Malaria, Public Health, Pediatric Infectious Disease, Tuberculosis and Transplant Infectious Disease.

In addition to a medical degree, ID doctors must complete a three year training residency in internal medicine as well as a two-year fellowship in infectious diseases, then pass the exam to become board certified. Patients will generally be referred to an ID doctor by a hospitalist if they have already been admitted to a hospital, or by their primary care physician.