Time trends in the burden of autoimmune diseases across the BRICS: an age–period–cohort analysis for the GBD 2019

This study aims to evaluate the long-term trend of prevalence and DALY (disability-adjusted life-year) rate on the age, period and cohort (APC) of the BRICS (Brazil, Russia, India, China and South Africa) country for autoimmune diseases (rheumatoid arthritis (RA), inflammatory bowel disease (IBD), multiple sclerosis (MS) and psoriasis).The data are sourced from the Global Burden of Disease Study 2019, and it uses the Joinpoint regression model to estimate the time trends of autoimmune diseases from 1990 to 2019. Additionally, it employs the Age-Period-Cohort (APC) model to estimate the age, period, and cohort effects from 1990 to 2019.For 1990 to 2019, the ASPR (age-standardised prevalence rate) of IBD increased significantly for China and South Africa, and decreased significantly for Brazil, India, Russian. The Russian ASPR of MS demonstrated a significantly decreasing trend (average annual percent change=-0.5%, 95% CI -0.6 to -0.5), with the most increased occurring in Brazil at 2009-2014. The cohort effect on DALY rates for Psoriasis displayed an ongoing decreasing trend from the 1929-1933 birth cohort to the 1999-2003 birth cohort. Specifically, the five countries relative risk values (RRs) of DALYs due to RA increased significantly by 7.98, 16.07, 5.98, 3.19, 9.13 times, from 20 to 24 age group to 65 to 69 age group.The population of the BRICS countries accounts for more than 40% of the global population. And we found that the age effect of various autoimmune diseases is heavily influenced by population ageing.