Incidence and Viral Etiology of Acute Respiratory Infections and Pneumonia among Children Under Two Years: A Birth Cohort Study in Dhaka, Bangladesh.

Globally, acute respiratory infections (ARI), including pneumonia, remain the leading infectious causes of morbidity and mortality among children under-two years of age. We conducted this longitudinal birth cohort study in a low-income urban community in Dhaka, Bangladesh, to estimate the incidence of ARI and pneumonia and assess their viral etiology. From May 2015 to March 2016, 447 children were enrolled and followed till 2022. In this analysis, we included data from the first two years of children's lives, which contributed to a total observation of 778 child-years. Nasopharyngeal wash samples were collected during symptomatic episodes, which were tested using rRT-PCR for rhinovirus (RV), respiratory syncytial virus (RSV), human metapneumovirus (hMPV), influenza virus, human parainfluenza virus (HPIV), and adenovirus. We calculated incidence rates using Poisson-based methods with 95% confidence intervals (CI) and stratified age-specific rates into three groups: 0 to <6 months, 6 to <12 months, and 12 to 24 months. A total of 2,335 ARIs and 314 pneumonia episodes were documented. At least one respiratory virus was detected in 71% of ARI and 75% of pneumonia episodes. RV was the most frequently detected virus (54% in ARI, 40% in pneumonia), followed by RSV, HPIV, and influenza. The incidence of viral ARI was 212/100 child-years (95% CI: 202-223), and that of viral pneumonia was 30/100 child-years (95% CI: 27-35). The observed incidence of viral ARI and pneumonia during early childhood underscores the need for targeted interventions. Future research should examine environmental and socioeconomic influences, assess preventive strategies, and improve early detection and treatment.