A systematic review of the pivotal role of environmental toxicant exposure on infectious diseases in low- and middle-income countries.

Objective: The objective of this review is to identify which environmental toxicants are linked to infectious diseases in low- and middle-income countries (LMICs) by synthesizing available evidence. It aims to summarize key findings, identify research gaps and provide policy recommendations based on the associations between specific toxicants and disease outcomes. Study design: Systematic review. Methods: We conducted a comprehensive search in PubMed, Scopus, Web of Science (core collection), and CENTRAL (the Cochrane Library) to identify studies on bacterial, viral, and parasitic pathogenic activity. Result: This search yielded 11,468 studies, of which 55 met inclusion criteria after screening following the standard methods. A consistent association is found between particulate matter (PM2.5 and PM10) exposure and increased respiratory infection risk, with PM2.5 particularly linked to increased incidence and mortality in diseases like COVID-19 and tuberculosis. Heavy metals, including lead, cadmium, and mercury worsen chronic infections such as HIV/AIDS and hepatitis by increasing body burden and inflammation. The review highlights air pollutants' substantial impact on infectious disease spread and severity while noting a research gap on other pollutants including persistent organic pollutants (POPs) and polycyclic aromatic hydrocarbons (PAHs). Bias assessment indicates around half the studies show low risk of bias; however, potential biases were noted in confounding variables and blinding of outcome assessment. Conclusion: The systematic review emphasizes the need for research on biological mechanisms underlying these associations and the impacts of other pollutants. Findings advocate for reducing environmental pollution exposure in LMICs to mitigate infectious disease risk.