Only one resource in North America offers complete disease information about a real population spanning half a century. Only one repository can be used to study almost any condition, pointing the way to new discoveries.

It's a treasure trove of data, funded by the National Institutes of Health (NIH) and used by researchers nationally, including the Institute of Medicine. The Rochester Epidemiology Project (REP) is one of a kind.

This collection of comprehensive medical records in the Rochester Epidemiology Project makes Olmsted County, Minn., the location of Mayo Clinic's Rochester campus, one of the few places in the world where scientists can study virtually an entire geographic population to identify trends in disease, evaluate treatments, and discover risk factors for various diseases and conditions. It's also proving to be an invaluable tool in finding new ways to protect people.

Why it's so important to research

Progress in medicine requires more than just the discovery of new medications and invention of new procedures. It also requires an evaluation of how care is being provided and its outcomes, both experimentally and as established practice. Connecting outcomes to variables such as a patient's age, sex, previous treatment or military service helps researchers develop better therapies.

The Rochester Epidemiology Project provides electronically linked medical records for the study of nearly any condition.

The Rochester Epidemiology Project is one of the few repositories in the world that:

• Covers a well-defined geographic region in order to minimize biases such as income and insurance coverage
• Spans a time frame that provides generational depth
• Covers enough patients — now at more than 500,000 and counting — so that inferences can be made from even relatively rare connections
• Includes as many electronically searchable variables as possible

The Rochester Epidemiology Project has supported more than 2,000 studies through the years, covering almost every medical specialty. In addition to the sheer volume of studies, research through the database has influenced policy, patients and medicine worldwide.

Notable research discoveries have shown that:

• Women who have their ovaries removed before menopause are at higher risk of dementia
• Skin cancer is up dramatically in people younger than 40, especially young women
• Smoke-free workplace laws save lives

The project's database is being used to design programs for new mothers, to determine compensation to veterans with post-traumatic stress disorder, and to better allocate health care resources.

A century in the making

The Rochester Epidemiology Project has its origins in the earliest days of Mayo Clinic.

Rather than having each physician or specialty keep separate records — and destroying them after seven years of inactivity — the Mayo brothers, Drs. William J. and Charles H., asked Dr. Henry S. Plummer in 1907 to devise a system that would collect and store all records for each patient, including physician examination notes, laboratory test results, correspondence with the patient, and birth and death records.

Under the leadership of neurologist and epidemiologist Leonard T. Kurland, M.D., who also served as chair of Mayo Clinic's Department of Medical Statistics and Epidemiology, Mayo Clinic obtained NIH funding in 1966 to link medical records from health care providers across the county, including Olmsted Medical Group (now Olmsted Medical Center) and the Rochester Family Medicine Clinic.

The Rochester Epidemiology Project was born.

"Mayo developed all of this infrastructure for the improvement of the practice, and also for the science," says neurologist and epidemiologist Walter A. Rocca, M.D., the Mayo Clinic Ralph S. and Beverley E. Caulkins Professor of Neurodegenerative Diseases Research and co-director of the Rochester Epidemiology Project since 2006.

Patients throughout Olmsted County are asked whether they agree to participate in the Rochester Epidemiology Project or to opt out of having their records available for research purposes. The approximately 95 percent participation rate "really affirms the concept that patients believe that their data should be used for the greater good," says Barbara Yawn, M.D., co-director of the project and research director at Olmsted Medical Center.

Eventually technology caught up, and in the first years of the new century, the records were computerized. At the same time, the REP Browser was created as a portal to allow the medical records to be electronically searched through a secure site.

With these changes, it became possible to quickly locate all the cases of patients who had similar diseases or who had undergone similar procedures.

"We recognize the potential for the Rochester Epidemiology Project as a valuable research resource that will enable the scientific community to address public health research questions of importance for the well-being of older Americans," says Chhanda Dutta, Ph.D., chief of the National Institute on Aging's Clinical Gerontology Branch. The NIH's National Institute on Aging has funded the project since 2010.

Still expanding

The Rochester Epidemiology Project has continued to expand under the leadership of Drs. Rocca and Yawn.

They have reached out to the research community and encouraged studies benchmarking the project's population as representative of the population of Minnesota, of the Upper Midwest, and of a major segment of the entire United States.

The Rochester Epidemiology Project is now expanding to include an 11-county region of southeastern Minnesota and to bring in other health care providers, such as dentists and chiropractors, allowing inferences drawn to carry even more statistical power. It is also integrating other types of data, such as drug prescriptions and immunizations.

Hot subjects for future research include socio-economic factors that may drive illness, spur recovery or maintain health; and health differences between urban and rural populations.

Although many studies have used the extensive historical database to improve patient care, two recent examples from the Rochester Epidemiology Project stand out: postpartum depression and head trauma.

Postpartum depression

When the postpartum depression study started in 1998, the condition had been common in new mothers yet it often went undiagnosed. But just how common it was and how commonly overlooked were open questions when Dr. Yawn and two Mayo Medical School students began to investigate.

They started the postpartum depression study using the Rochester Epidemiology Project because Dr. Yawn says she knew they could understand on a population basis what was happening.

Their three-part study began by determining how often postpartum depression was being diagnosed in Olmsted County. "It turned out that it was seldom recognized (by the health care system)," Dr. Yawn says.

Next, the researchers introduced a standard screening test for all women after giving birth and then reviewed the results of the screening.

"The important part was looking to see if that improved the rates of diagnosis and the rates of people who were treated, and it did," Dr. Yawn says.

Dr. Yawn and the other researchers then designed a national study to teach providers how to screen for postpartum depression and how to refer patients for treatment.

That study was repeatedly cited in an Institute of Medicine (IOM) report on depression in parents and was one of the first in the nation that was successful in making a statistical difference in patient impact, Dr. Yawn says. Information gleaned from the study can also help women make informed decisions about the possible benefits and risks of treating postpartum depression.

The study on postpartum depression is now being implemented in several European countries.

Head trauma

For more than 20 years, Mayo Clinic researchers have used data from the Rochester Epidemiology Project to examine what happens to patients who have experienced head trauma, sometimes even decades earlier. Researchers have explored links to dementia, Parkinson's disease, epilepsy and many other potential consequences of head trauma.

When the U.S. Congress in 2008 needed to decide how to compensate military personnel who had experienced head trauma, it asked the Institute of Medicine for help. And the IOM cited the Rochester Epidemiology Project's studies as key pieces of evidence.

"We were very pleased that they picked our studies, based on our resources, to convince Congress to take a decision one way or another," Dr. Rocca says. "That we had the data to inform a decision for them was also very exciting. This reconfirmed how important this research is, that what we do here in Olmsted County in Minnesota helps influence decisions of the federal government."

Because of its long and complex history, the Rochester Epidemiology Project will continue to be the foundation for studies that transform medical practices and policies in Olmsted County, the country and the world. It provides knowledge, guidance and insight for medical researchers trying to keep people healthy.

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