Malnutrition-Infection Syndemics in Pediatric Populations: A Systematic Review

Malnutrition and infectious disease act together in children through a mutually reinforcing, or syndemic, relationship that is biologically and socially distinct from simple comorbidity, and this interaction remains a leading driver of child morbidity and mortality in low- and middle-income countries (LMICs). This review critically synthesizes epidemiological, mechanistic, and clinical evidence on malnutrition-infection syndemics in children aged 0–59 months, drawing on a systematic search of PubMed, Scopus, Web of Science, ScienceDirect, and reports from WHO, UNICEF, and FAO published mainly between 2015 and 2024, following PRISMA guidance for study identification and thematic narrative synthesis. The evidence consistently shows bi-directional links between malnutrition and diarrhoeal disease, pneumonia, malaria, and tuberculosis, mediated by immunological impairment, mucosal barrier disruption, gut dysbiosis, environmental enteric dysfunction, and micronutrient deficiency, and compounded by poverty, poor sanitation, and food insecurity. Integrated nutrition-infection interventions consistently outperform siloed, vertical programmes. The review's central contribution is to bring these strands together across four major childhood infections and the microbiome-immunity axis within a single synthetic framework, rather than treating each association in isolation as prior narrower reviews have done. Key limitations include the narrative rather than quantitative (meta-analytic) synthesis method and reliance on published, English-language literature, which may under-represent grey literature and non-English research. We conclude that multisectoral interventions addressing nutritional rehabilitation, infectious disease control, and structural determinants together are needed, and that mechanistic understanding of the gut microbiome, long-term developmental outcomes, and implementation science for integrated delivery remain priority areas for future research and investment.