Trends in the incidence rates of stroke in Rochester, Minnesota, since 1935

The Mayo Clinic medical records system and records-linkage system have been used to study trends in the incidence of stroke in Rochester, Minnesota, for comparison with U.S. stroke mortality trends. This study extends the observations back through 1935. The average annual incidence rate for the period 1935 to 1944 was 188 and 179 per 100,000 population for men and women, respectively--not significantly different from 200 for men and 178 for women for the period 1945 to 1954. The blood pressure level in these patients did not affect probability of survival or recurrent stroke. The trend in the incidence rate of stroke for women showed no change for the 20 years from 1935 to 1954, after which there was a gradual decline. For men there was little change until 1969, after which there was a sharp decline. We suggest that the gradual decline in U.S. stroke mortality rates for this early period may include an artifact introduced by changing codes and changing fashions of diagnosis.