Rochester Epidemiology Project

The Rochester Epidemiology Project (REP) is a population-based medical records linkage system that was established by Leonard T. Kurland in 1966. It exploits the geographic isolation of Olmsted County in southeastern Minnesota from other urban centers so that almost all medical care for residents of the county (or the central city of Rochester) is delivered within the community. Care is mainly provided by Mayo Clinic and Olmsted Medical Center. Mayo Clinic is a major referral center but has always provided primary, secondary, as well as tertiary care to local residents. It employs a dossier (or unit) medical record for each individual containing the details of every admission to its two affiliated hospitals (St. Marys and Rochester Methodist), every outpatient office or clinic visit, all emergency room and nursing home care, all laboratory results, all pathology reports including autopsies, and all correspondence concerning each patient.

Mayo Clinic now holds medical histories on more than 6.3 million unique individuals (including referral patients); less than a 1,000 of these dossiers have been lost over the past century. The records of the other providers have also been maintained and are available for use in approved research studies. These original and complete (inpatient and outpatient) records that span each person's entire period of residency in the community are easily retrievable for study because Mayo has maintained, since 1910, extensive indices based on clinical and histologic diagnoses and surgical procedures. With continuous support from the NIH for the past 40 years, the REP created similar indices for the records of the other providers of medical care to county residents, most notably Olmsted Medical Center with its affiliated Olmsted Community Hospital.

The result is a unique medical record system capable of addressing research questions in a community population with more than 5.2 million person-years of experience from 1950 through 2005. These detailed data, accumulated over a long period of time, have provided the basis for almost 1,700 studies by investigators inside and outside Mayo. Most of these studies could not have been carried out as efficiently anywhere else. Complete ascertainment of diagnosed cases supports descriptive studies of the incidence and outcomes of diverse diseases and diagnostic/therapeutic procedures. Inception cohorts with verified exposures can be identified for long-term retrospective (historical) cohort studies, and the local community can be enumerated and sampled for population-based crosssectional and case-control studies. Due to the nature of the database, the main focus has been on clinical risk factors and clinical outcomes; because of the contemporary documentation available, these are much more accurately ascertained compared with self-report. The population of Olmsted County was 124,000 in 2000 and is largely white (99% in 1950, 90% in 2000). Except for a higher proportion of the working population in the health care industry, its population resembles U.S. whites generally. Judged by previous studies of a variety of chronic diseases, results can probably be extrapolated to that population.