Abstract
Acute respiratory infections (ARI) remain a major cause of child mortality in low- and middle-income countries. However, the risk factors for ARI are poorly understood in low-income settings, and ARI aetiology is changing, driven by vaccination. There are very limited data from Lao PDR (Laos) on ARI aetiology and risk factors to support health policy decisions. This study aimed to investigate the aetiology of hospitalised ARI, and describe risk factors associated with hospitalised ARI, in children under 5 years of age in Laos. We conducted a case–control study at Mahosot Hospital, Laos, enrolling children under five years of age hospitalised with ARI, and community controls matched on age, sex and time of recruitment. Demographics and clinical characteristics were collected, and throat swabs taken. Swabs were analysed using probe-based real-time polymerase chain reaction (PCR) to detect bacterial and viral microorganisms. Risk factors for ARI were determined through regression analysis, and microorganism-specific attributable fractions (AF) were calculated to estimate each microorganism’s contribution to hospitalised ARI. We enrolled 307 cases and 564 controls over 12 months in 2016/17. Microorganisms were detected in 93.8% of cases and 58.9% of controls. Respiratory syncytial virus (RSV) was the leading viral cause of hospitalised ARI, attributed to 29.6% of cases, followed by influenza viruses (11.6%). H. influenzae was attributed to 40.8% of cases. RSV exhibited clear seasonality, peaking during the wet season. Exclusive breastfeeding for 3 months (OR: 0.62; 95% CI 0.45–0.86), and being up to date with pneumococcal conjugate vaccination (odds ratio: 0.6; 95% CI 0.41–0.80), were associated with a lower risk of hospitalised ARI; while low birth weight (OR: 2.91; 95% CI 1.63–5.28), and household smoking (OR: 3.07; 95% CI 2.25–4.18), were associated with increased risk. RSV and H. influenzae remain major causes of ARI in Laos. The findings highlight the potential benefit of tailoring interventions to the local context, including vaccination and risk mitigation strategies, to reduce the burden of ARI in Laos and other low and middle-income countries.
Data availability
The individual participant data generated in this study are not publicly available due to data governance requirements. Specifically, data access is subject to approval by the Murdoch Children’s Research Institute (MCRI) Change Advisory Board, the Royal Children’s Hospital Human Research Ethics Committee, the National Ethics Committee for Health Research, Ministry of Health, Laos and the Oxford Tropical Research Ethics Committee. Academic researchers may request access to de-identified data. Requests will be reviewed by the MCRI Change Advisory Board and relevant ethics committees. If approved, data will be shared under a data sharing agreement.
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Acknowledgements
Firstly, we would like to thank all the participants in the study. We also thank the Director and staff of Mahosot Hospital, especially Malavanh Vongsouvath, Van Hoan Nguyen and the team at the microbiology laboratory for their technical help and support.
Funding
This study was funded by the Institute of Research for Development (IRD), Aix-Marseille University, the Wellcome Trust of Great Britain. The fieldwork and pneumococcus testing were supported by the Bill & Melinda Gates Foundation grant OPP1115490 and the Murdoch Childrens Research Institute, Melbourne, Australia. FMR and JDH are supported by Australian National Health and Medical Research Council (NHMRC) Investigator Grants. We also acknowledge the Victorian Government′s Operational Infrastructure Support Program. This research was funded in whole, or in part, by the Wellcome Trust [grants 089275/H/09/Z0, 106698/Z/14/Z and 220211]. For the purpose of Open Access, the author has applied a CC BY public copyright licence to any Author Accepted Manuscript version arising from this submission. The funders of the study had no role in study design, data collection, data analysis, data interpretation, or writing of the report.
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Conceived and designed the analysis: ADP, PNN, XDL, FMR. Collected the data: MaMa, DABD, KV, TB, SP, JL. Contributed data or analysis tools: XDL, JDH. Performed the analysis: ADP, RL, MeMo, JDH, CS. Wrote the paper: ADP, JDH, FMR, CS, PNN.
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Hart, J.D., Dance, D.A.B., Vilivong, K. et al. Aetiology of acute respiratory infection in Vientiane, Lao PDR, from a case–control study. Sci Rep (2026). https://doi.org/10.1038/s41598-026-41321-9
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DOI: https://doi.org/10.1038/s41598-026-41321-9
