Incidence of Alzheimer's disease in India: A 10 years follow-up study

Objective: To determine overall and age-specific incidence rates of Alzheimer's disease (AD) in a southern Indian province, Kerala. Materials and Methods: A 10-year (2001-2011) prospective epidemiologic study of community residing subjects aged >= 55 years at enrollment. The catchment area included four urban and semi-urban regions of Trivandrum city in Kerala, India, was selected to provide a range of demographic and socioeconomic representation. Cognitive and functional ability screening were done at baseline and 24-month follow-up assessments. Consensus diagnostic procedures were done using the Diagnostic and Statistical Manual of Mental Disorders, 4th edition (DSM-IV), and the National Institute of Neurological and Communicative Disorders and Stroke - Alzheimer's Disease and Related Disorders Association (NINDS-ADRDA) criteria for the diagnosis of dementia and AD. Results: Among the 1066 eligible participants who were cognitively normal at baseline, 104 developed dementia (98 with AD) over a follow-up period of 8.1 years. The incidence rates per 1000 person-years for AD was 11.67 (95% CI: 10.9-12.4) for those aged >= 55 years and higher for those aged >= 65 years (15.54, 95% CI: 14.6-16.5). In those aged >= 65 years, the world age standardized incidence rate was 21.61 per 100,000, and standardized against the age distribution for the year 2000 U. S. Census, the age-adjusted incidence rate was 9.19 (95% CI: 9.03-9.35) per 1000 person-years. Incidence rate of AD increased significantly and proportionately with increasing age. Conclusion: These are the first AD incidence rates to be reported from southern India. The incidence rates appear to be much higher than that reported from rural north India, comparable with that reported from China, and marginally lower than that reported from the western world.