I do not know why I never thought about this before, but whenever I peruse the match lists for universities, these are the specialties I come across: anaesthesia, neurology, neurosurgery, OB/GYN, psychiatry, pediatrics, internal medicine, family medicine, emergency medicine, orthopedics, general surgery, radiology, physical medicine and rehabilitation (PM&R) and pathology. Somehow it did not occur to me to ask why no one goes into a cardiology residency, or a gastroenterology (GE) residency.
I am sure we learned about it at some point in MED at UCSD, but those extra specialties are actually subspecialties of internal medicine. So, if you want to go into cardiology or GE, you'll start out in internal medicine for three years and then proceed to a fellowship in the subspecialty of your choice. Here are the 13 commonly recognized subspecialties: adolescent medicine, allergy and immunology, cardiology, endocrinology, GE, geriatrics, hematology, infectious disease, nephrology, oncology, pulmonology, rheumatology, and sports medicine. Others that may fall under one of the above categories include: transplant hepatology, sleep medicine, clinical cardiac electrophysiology, critical care medicine, interventional cardiology, and nuclear medicine.
The duration of each fellowship varies from 1-3 years. Since I have been reconsidering infectious disease as a specialty, I tried to find out how competitive it is compared to other subspecialties of internal medicine. According to most websites and forums, specialties are more competitive based upon the eventual salary, so the specialties with more expensive procedures are reimbursed more for services. The most competitive are cardiology, GE, Allergy/Immunology, and Hematology/Oncology. The least competitive, to my relief, were geriatrics, rheumatology, and infectious disease! So now the plan is to go into internal medicine and from there decide in what to subspecialize. Even if I do not subspecialize, internal medicine deals with difficult diagnoses and treatments, which I find quite interesting!