Incidence, prevalence, and national burden of interstitial lung diseases in India: Estimates from two studies of 3089 subjects

Background and objective The epidemiology of interstitial lung diseases (ILDs) in developing countries remains unknown. The objective of this study was to estimate the incidence, prevalence, and national burden of ILDs in India. Methods Data of consecutive subjects (aged >12 years) with ILDs included in a registry between March 2015 and February 2020 were analyzed retrospectively. The proportion of each ILD subtype was determined. The crude annual incidence and prevalence of ILDs for our region were estimated. Subsequently, the primary estimates of the national annual incident and prevalent burden of ILD and its subtypes were calculated. Alternative estimates for each ILD subtype were calculated using the current and a large, previous Indian study (n = 1,084). Data were analyzed using SPSS version 22 and are presented descriptively. Results A total of 2,005 subjects (mean age, 50.7 years; 47% men) were enrolled. Sarcoidosis (37.3%) was the most common ILD subtype followed by connective tissue disease (CTD)-related ILDs (19.3%), idiopathic pulmonary fibrosis (IPF, 17.0%), and hypersensitivity pneumonitis (HP, 14.4%). The crude annual incidence and prevalence of ILDs were 10.1-20.2 and 49.0-98.1, respectively per 100,000 population. The best primary estimates for the crude national burden of all ILDs, sarcoidosis, CTD-ILD, IPF, HP, and other ILDs (in thousands) were 433-867, 213-427, 75-150, 51-102, 54-109, and 39-78. The respective alternative estimates (in thousands) were sarcoidosis, 127-254; CTD-ILD, 81-162; IPF, 46-91; HP, 130-261; other ILDs, 49-98. Conclusion In contrast to developed countries, sarcoidosis and HP are the ILDs with the highest burden in India.