The aging of the U.S. population is translating into many more visits to doctors' offices and hospitals, a reality that is taxing weak spots in the health-care system, according to a government report released Wednesday.

People made an average of four visits a year to doctors' offices, emergency rooms and hospital outpatient departments in 2006, a total of 1.1 billion visits.

The number of medical visits increased 26% between 1996 and 2006, significantly higher than the 11% population growth during that period.

The population is aging, and older people are more likely to seek medical care, says Catharine Burt of the Centers for Disease Control and Prevention's National Center for Health Statistics.

And today's seniors make more visits to the doctor than older people did 10 years ago, she says.

"Older people represent a larger proportion of the hospital inpatient case load," Burt says. "They have more complications and have to have more done for them. So that makes the job of the nurses and people taking care of hospital patients much harder than it was 30 or 40 years ago."

Meanwhile, patients waited an average of about 56 minutes to see a doctor in the emergency room in 2006, up from 38 minutes in 1996.

The longer wait may be because more patients are going to a declining number of hospital emergency departments, Burt says.

But the statistic is somewhat misleading because it is affected by statistics from large urban hospitals where it's not unusual to wait longer than an hour. A typical wait is about 30 minutes, she says. People usually don't wait very long in smaller communities.

The most common reasons adults give for going to the emergency room include chest pain, abdominal pain, back pain, headache and shortness of breath.

The most common reasons for emergency room visits for children under 15 are fever, cough, vomiting, earache and injuries to the head, neck and face.

Other findings:

• Half of all trips to doctors' offices were made by people with chronic medical conditions. High blood pressure was the most common ailment, followed by arthritis, high cholesterol, diabetes and depression.

• Seven of 10 visits to doctors' offices, emergency rooms and hospital outpatient departments resulted in at least one medication being either provided, prescribed or renewed for a total of 2.6 billion prescriptions. Painkillers were the most commonly prescribed medication and the ones most used at primary-care facilities and in emergency rooms.

• The rate of knee replacement surgeries doubled for people ages 45-64 between 2000 and 2006.

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