Health care reform is a locomotive barreling down America’s tracks. In two years, the Affordable Care Act (ACA) will cover some 30 out of 50 million of us that currently lack health insurance. Political beliefs aside, it would seem that supplying insurance to protect the health of more people is a societal good. Though the costs of reform will be debated for years to come, one major question remains that has not been adequately addressed:

Who will see all the new patients?

It’s no secret that there’s a looming crisis in primary care. Estimates place the shortfall of doctors at 30,000 in the next couple of years. Yet medical schools are flush with applicants. Residency slots are filling at higher rates than ever before as new medical schools have been chartered and class sizes have expanded. So where are all the new doctors?

In a word, the hospital.

“Hospital medicine is the fastest growing specialty in American medical history,” said Dr. Robert Wachter, chief of the division of hospital medicine at the University of California, San Francisco, and the man credited with coining the term “hospitalist” in 1996. According to statistics compiled by the Society of Hospital Medicine (SHM), the number of doctors practicing as hospitalists has increased 172 percent from 2003 to 2010. There are now more than 30,000 doctors nationwide that are classified as hospitalists: physicians who take care of hospitalized patients but no longer have office-based practices or do primary care.

To understand how difficult it will be to find a primary care doctor in two years, look no further than Massachusetts. In 2006 the state passed a health care law mandating that everyone obtain insurance (sound familiar?). For those unable to afford the cost, subsidies were made available.

Within weeks, the “uninsurance” rate in Massachusetts dropped precipitously. Commensurate with that was a rise in both the number of “closed” office practices and the length of time it took to get a new patient appointment. Nearly six years after the law passed, more than half of the family practice and internal medicine offices in the state are closed to new patients. According to the Massachusetts Medical Society, the average wait for a new patient to be seen by an internist is 48 days. Turns out insurance doesn’t guarantee access after all.

For young doctors just finishing residency, practicing as a hospitalist has many attractions. The most enticing aspects are financial and lifestyle considerations. A starting hospitalist (depending on what region of the country they practice in) can earn around $200,000 per year (a starting office-based internist will make in the neighborhood of $150,000). Perhaps more importantly, many hospitalist groups operate with “seven-on/seven-off” schedules. This means that a hospitalist earns that salary working seven consecutive days followed by seven days off. This option is extremely popular with doctors that are parents, as well as those that want to earn extra income or volunteer during their off time.

During the three-year internal medicine residency (like the kind I administer), doctors-in-training will spend about two-thirds of their time on hospital-based rotations. If familiarity breeds comfort, then it’s not a surprise that recent residency graduates choose to stay in an environment to which they’re well-adapted. And since hospital work is shift work, there is no on-call or after-hour responsibilities to handle. When a hospitalist leaves the hospital, they’re done — unlike office-based internists who still carry pagers and get middle of the night phone calls.

Couple the lifestyle and the training experience with the huge debt burden that U.S. medical students accrue, and deciding on a hospitalist career becomes a rational choice. Dr. Wachter of UCSF compares hospital medicine to site-based specialties that came before it: emergency medicine and critical care. All of these specialties represent a convergence of high-complexity and high-cost care in a single location, where it makes sense to have well-trained specialists who handle the specific set of problems encountered there.

Since the severity of illness seen by hospitalists tends to be high, specialization improves safety and quality, which are key metrics for hospitals as insurers now tie payment to such indices. Hospitals have almost all transitioned to hospitalist models to at least some degree. According to SHM data, the larger the hospital, the more likely it is to have hospitalists. Management likes the efficiency and improved patient satisfaction that comes with having doctors on the premises at all times. Earlier discharges and shorter lengths-of-stay for patients keep the hospital beds turning over and consequently the reimbursement dollars flowing in.

Contrast all of this to the realities of office practice: Fifteen-minute visits with patients on multiple medications, oodles of paperwork that cause office docs to run a gauntlet just to get through their day, and more documentation and regulatory burdens than ever before (e.g. new IT and compliance mandates). Students see the high pressure that primary care docs are under and are increasingly making the logical choice.

A colleague of mine recently sent shock waves through our community by leaving her internal medicine practice after 23 years to become a hospitalist. Her patients were devastated, as they had grown deeply attached to her. Yet with a child entering high school, my colleague felt that the seven-on/seven-off schedule and increased pay would dramatically improve the quality of her life and time available for her family. She was frustrated after spending all day seeing patients in an office only to come home and have at least two more hours of documentation to complete most nights.

Yet despite all of the negativity surrounding primary care, there are still holdouts.

Dr. Diane Fingold, an internist at Massachusetts General Hospital in Boston, gave voice to the downtrodden in a piece published in the New England Journal of Medicine in December. In “The Road Less Travelled,” Fingold wrote beautifully of her attachment (and the above and beyond care she provided) to a patient who’d suffered a stroke and was immobilized and unable to speak. These medical complications made it nearly impossible for the patient to advocate for herself when the pharmacy withheld her medications due to an insurance snafu. After a number of phone calls, Fingold succeeded for her patient.

It’s that deep commitment over time, all the ups and downs of her patient’s many hospitalizations that keep Fingold in the game. She writes:

I get the call and head over to the ED. As I pull back the curtain, a smile of recognition spreads over Mary’s face. She can relax now. She knows I care, that I’ll figure out her story and make sure the ED docs know all her meds, allergies, and complications; I’ll let her specialists know she’s here. She knows that if her medicines change, I’ll contact her pharmacy to ensure she gets a new blister pack. She lies back and breathes more comfortably.

Familiarity has built a fortress of trust between this patient and her doctor. Fingold concludes: “And at times like this, I recognize my deep satisfaction with the road I’ve chosen to travel.”

When I called Fingold, she told me that her hospital wants to transition as quickly as possible to a hospitalist system. But pockets of resistance remain. In her practice (which is on the hospital’s campus), all of the doctors see their own patients when they are hospitalized. In her case, proximity (and desire) allows her to be directly involved in her patients’ care. But for most of us, the luxury of having our own doctor treat us in the hospital is a thing of the past.

“Ultimately, I believe we will have to give it up,” Fingold told me. “I think it will be sad.”

John Schumann is an internal medicine physician who blogs at GlassHospital.  This article originally appeared in The Atlantic.