Risk factors and aetiological agents of community-acquired pneumonia in children under five years in South Asia: A systematic review

Pneumonia remains a leading cause of mortality among children under five years in South Asia, a region that, with sub-Saharan Africa, accounts for over half of the world's childhood pneumonia cases. To our knowledge, no prior review has jointly synthesised the risk factors and aetiological agents of community-acquired pneumonia (CAP) in under-fives specific to this region. This systematic review aimed to identify, critically appraise, and synthesise available evidence on the risk factors and aetiological agents associated with CAP in children under five years of age in South Asian countries. Following PRISMA guidelines, four electronic databases (MEDLINE, PubMed, Global Health, and Web of Science) were systematically searched for studies published between January 2000 and July 2024, with the search updated to January 2026. Quality assessment was performed using the Crowe Critical Appraisal Tool (CCAT), with only high-quality studies (≥75% score) included in the final synthesis. Data were synthesised narratively due to heterogeneity in study designs and outcome measures. From 1196 records identified and 747 studies screened, 16 met the inclusion criteria after quality assessment (8 on risk factors, 8 on aetiology), conducted across five South Asian countries (India, Bangladesh, Nepal, Pakistan, Bhutan). Young age (children 0–23 months), malnutrition (particularly underweight and wasting), and incomplete immunisation emerged as the most consistently identified risk factors across studies. Environmental exposures, including indoor air pollution, poor ventilation, and overcrowding, were significant contributors. Viral pathogens predominated in aetiological studies, with respiratory syncytial virus being the most frequently identified pathogen (mean detection rate 29.2%). Blood culture positivity for bacterial pathogens was generally lower (1.5-31.3%; below 13% in four of five studies), with Streptococcus pneumoniae and Staphylococcus aureus most common among positive cultures. This systematic review demonstrates that childhood CAP in South Asia results from a complex interplay of modifiable host, environmental, and socioeconomic risk factors. Integrated interventions addressing nutrition, immunization coverage, household air pollution, and socioeconomic determinants are essential for reducing the substantial pneumonia burden among South Asian children.