Age-Specific Incidence of Alzheimer's Disease in a Community Population

To determine age-specific incidence rates of clinically diagnosed Alzheimer's disease. —Cohort, followed a mean of 4.3 years. —East Boston, Mass. —Of 2313 persons aged 65 years and older who were initially free of Alzheimer's disease, 1601 participated in the ascertainment of incident disease (80% of survivors), 409 declined participation, and 303 died before the end of the follow-up period. A stratified sample of 642 persons received detailed clinical evaluation. —Diagnosis of new probable Alzheimer's disease through structured clinical evaluation including neurologic, neuropsychological, and psychiatric examination. Community incidence rates were computed by 5-year age groups, adjusted for gender, single year of age, length of follow-up interval, and sampling design. —The estimated annual incidence of Alzheimer's disease in the population was 0.6% (95% confidence interval [Cl], 0.3% to 0.9%) for persons aged 65 to 69 years, 1.0% (95% Cl, 0.6% to 1.4%) for persons aged 70 to 74 years, 2.0% (95% Cl, 1.3% to 2.7%) for persons aged 75 to 79 years, 3.3% (95% Cl, 2.2% to 4.4%) for persons aged 80 to 84 years, and 8.4% (95% Cl, 3.7% to 13.1%) for persons aged 85 years and older. —The incidence of Alzheimer's disease is substantial and is approximately 14 times higher among persons older than 85 years compared with those between 65 and 69 years of age.