In the developing countries approximately 1 out of 8-10 people are hospitalized each year for one reason or another; this rate is much higher for the elderly (above age of 65), which becomes 1 out of 3-4 people each year. 
The introduction of electronic medical records and highly advanced and sophisticated diagnostic tools and monitoring devices has made the hospital environment more complex than it used to be in the past. Additionally, hospitalization-related iatrogenic harms, which include infection, thrombosis, bed ulcers, medication errors, among others, have been recognized and the data show that the hospitalization risk is proportionally to the length of stay. 
The need for highly effective and highly skilled physicians to take care of hospitalized patients has been recognized a long time ago for the critical care units. However, the need for highly skilled physicians to take care of hospitalized patients, who do not need a critical care unit, has not been recognized until the past 10-20 years. Most USA hospital now employ special physicians whose role is to facilitate and integrate the care of the hospitalized patient so a timely diagnostic, therapeutic and discharge decision is made. 
In the UK, the equivalent to the Internist would be the Acute Physician, a skilled clinician who has clinical responsibility for all medical emergency patients admitted for assessment to UK Acute Hospital Trusts. Many UK Trusts also utilize the skills of the Acute Physician to provide an emergency outreach service to patients whose medical condition deteriorates while an inpatient in the hospital. ​