Incidence of Alzheimer's disease in a rural community in India - The Indo-US Study

Objective: To determine overall and age-specific incidence rates of AD in a rural, population-based cohort in Ballabgarh, India, and to compare them w ith those of a reference US population in the Monongahela Valley of Pennsyl vania. Methods: A 2-year, prospective, epidemiologic study of subjects aged greater than or equal to 55 years utilizing repeated cognitive and functio nal ability screening, followed by standardized clinical evaluation using t he Diagnostic and Statistical Manual of Mental Disorders, 4th edition, and the National Institute of Neurological and Communicative Disorders and Stro ke-Alzheimer's Disease and Related Disorders Association criteria for the d iagnosis, and the Clinical Dementia Rating scale for the staging, of dement ia and AD. Results: Incidence rates per 1000 person-years for AD with CDR g reater than or equal to0.5 were 3.24 (95% CI: 1.48-6.14) for those aged gre ater than or equal to 65 years and 1.74 (95% CI: 0.84-3.20) for those aged greater than or equal to 55 years. Standardized against the age distributio n of the 1990 US Census, the overall incidence rate in those aged greater t han or equal to 65 years was 4.7 per 1000 person-years, substantially lower than the corresponding rate of 17.5 per 1000 person-years in the Monongahe la Valley. Conclusion: These are the first AD incidence rates to be reporte d from the Indian subcontinent, and they appear to be among the lowest ever reported. However, the relatively short duration of follow-up, cultural fa ctors, and other potential confounders suggest caution in interpreting this finding.