Infectious disease is a subspecialty of internal medicine. It is not a separate medical specialty but rather an advanced branch that physicians pursue after first completing training and board certification in internal medicine. The American Board of Internal Medicine (ABIM) oversees certification in infectious disease, and candidates must already hold ABIM certification in internal medicine before they can even apply.
How Infectious Disease Fits Within Internal Medicine
Internal medicine is a broad specialty focused on the prevention, diagnosis, and treatment of adult diseases. Within that umbrella, there are more than 20 recognized subspecialties, and infectious disease is one of them. Others include cardiology, gastroenterology, and rheumatology. What all these subspecialties share is a common foundation: every physician practicing in one of them started as a general internist.
The ABIM, which is a member of the American Board of Medical Specialties (ABMS), sets the certification standards. To sit for the infectious disease board exam, a physician must already be board-certified in internal medicine. There is no shortcut or alternative entry point from a different specialty on the adult medicine side.
Training Path From Medical School to ID Specialist
The journey is long. After four years of medical school, a physician completes three years of internal medicine residency. That categorical residency, as the American College of Physicians describes it, makes them eligible for board certification as a general internist. Only then can they enter a fellowship in infectious disease.
The fellowship itself is 24 months, as required by the Accreditation Council for Graduate Medical Education (ACGME). During those two years, fellows train in clinical management of complex infections, laboratory microbiology, hospital epidemiology, and antimicrobial stewardship. That adds up to roughly nine years of training after college before a physician is a fully credentialed infectious disease specialist.
What ID Specialists Do That General Internists Don’t
A general internist handles a wide range of conditions and can treat many common infections, from urinary tract infections to pneumonia. The infectious disease specialist gets called in when things get complicated. That includes drug-resistant organisms like MRSA, infections in patients with weakened immune systems (such as those with HIV/AIDS or organ transplants), unusual or emerging infections, and cases where standard antibiotics have failed.
ID specialists also play a central role in hospital infection control. One of their most important functions is antimicrobial stewardship: programs designed to make sure antibiotics are used correctly across an entire hospital. Columbia University’s stewardship program, for example, involves daily interventions to optimize antibiotic therapy, combining formulary restrictions, education, surveillance of resistance patterns, and review of individual prescriptions. Research shows these programs work best when led by infectious disease physicians alongside specially trained pharmacists.
Beyond day-to-day patient care, ID doctors are often the first responders during outbreaks. They were critical during the HIV/AIDS epidemic, the SARS outbreak, anthrax bioterrorism events, and more recently during COVID-19. Their expertise in containment, isolation protocols, and rapid clinical diagnosis makes them essential during public health emergencies.
Pediatric Infectious Disease Is a Different Path
If a physician wants to treat infectious diseases in children rather than adults, the training pathway runs through pediatrics, not internal medicine. A pediatric ID specialist completes a pediatrics residency and then a pediatric infectious disease fellowship. Some programs offer a combined track: physicians who complete both internal medicine and pediatrics residencies can enter a combined Med-Peds infectious disease fellowship, spending one year focused on adult ID and another on pediatric ID. Children’s National Hospital and the NIH jointly run one such program, with rotations split between adult and pediatric clinical services.
The ID Workforce Today
Infectious disease is one of the smaller internal medicine subspecialties. As of 2023, there were roughly 10,500 active infectious disease physicians in the United States, with about 7,925 of them in direct patient care, according to data from the Health Resources and Services Administration. For context, the U.S. faces a projected shortage of over 141,000 physicians across all specialties by 2038. Infectious disease has faced its own recruitment challenges, partly because ID specialists tend to earn less than physicians in procedure-heavy subspecialties like cardiology or gastroenterology, despite comparable training length.
This workforce pressure means ID consultation may not always be readily available at smaller or rural hospitals, which is one reason antimicrobial stewardship guidelines and telemedicine ID consultations have become increasingly important tools for extending the reach of these specialists.