The injuries included: being given the wrong medication, having an allergic reaction to a medication, or receiving any treatment that led to more complications of an existing medical problem.
"These injuries are caused by the medical care or management rather than any underlying disease," said lead researcher Mary Carter, director of the Gerontology Program at Towson University in Maryland.
About two-thirds of these injuries occurred during outpatient care, rather than in the hospital, the study findings showed.
While there has been a great deal of effort in trying to understand medical injury in hospitals, not as much has been done in clinics, doctor's offices, outpatient surgery centers, emergency rooms and nursing homes, noted Carter.
"To really improve our ability to prevent these types of adverse events, we have to focus at least as much on outpatient care as we do on inpatient care," Carter said.
Findings from the study were published online May 27 in the journal Injury Prevention. It's important to note that while the people in the study all had Medicare insurance, the study didn't show that having Medicare insurance caused any of these injuries.
For the study, Carter and her colleagues collected data on more than 12,500 Medicare patients who made claims between 1998 and 2005. Their average age was 76.
The researchers found that 19 percent of those included in the study experienced at least one adverse medical event. That's higher than previous research estimates that suggested the rate of adverse medical events was probably around 13.5 percent for hospitalized patients, according to background information in the study.
"The rate of these injuries is probably higher than has been estimated," she said.
Sixty-two percent of these injuries took place during outpatient care, the investigators found.
Older people, men and those from lower-income backgrounds were most at risk of an adverse medical event, the study authors found. They also found that people who had chronic medical conditions or who were disabled in some way were more at risk of a medical injury.
Each additional month of age was associated with a 1 percent increase in the risk of a medical injury. In addition, the risk of experiencing an adverse medical event increased by 27 percent for each chronic condition a person had, the report revealed.
The death rate among those who had experienced a medical injury was nearly twice as high as among patients who hadn't had one, Carter said.
The consequences of these injuries were lasting. "We are seeing increased health care costs over a year following the injury with the greater use of medical services," said Carter.
Dr. David Katz is director of the Yale University Prevention Research Center and president of the American College of Lifestyle Medicine. He said: "We have long known that medical care, while pledged to avoid harm above all, actually imposes quite a bit of it. Medical injury is all too common, and adverse effects of treatment are common, even in the absence of error."
But, he added, a process of continuous assessment and systems-level reform is needed to reduce medical errors to the minimum.
"There is also need to cultivate more health by living well," he said. "Medical injuries occurred in the context of treatment, and were more common with more serious conditions. That older patients with several chronic diseases and on multiple medications are more prone to adverse medical events is less than shocking."
For more about patient safety, visit the National Patient Safety Foundation.