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 with those of a reference US population in the Monongahela Valley of Pennsylvania. Methods: A 2-year, prospective, epidemiologic study of subjects aged greater than or equal to 55 years utilizing repeated cognitive and functional ability screening, followed by standardized clinical evaluation using the Diagnostic and Statistical Manual of Mental Disorders, 4th edition, and the National Institute of Neurological and Communicative Disorders and Stroke-Alzheimer's Disease and Related Disorders Association criteria for the diagnosis, and the Clinical Dementia Rating scale for the staging, of dementia and AD. Results: Incidence rates per 1000 person-years for AD with CDR greater than or equal to0.5 were 3.24 (95% CI: 1.48-6.14) for those aged greater 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 distribution of the 1990 US Census, the overall incidence rate in those aged greater than 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 Monongahela Valley. Conclusion: These are the first AD incidence rates to be reported from the Indian subcontinent, and they appear to be among the lowest ever reported. However, the relatively short duration of follow-up, cultural factors, and other potential confounders suggest caution in interpreting this finding.