Burden and Distribution of Protozoan Pathogens in Diarrhea Cases Worldwide: A Systematic Review and Meta-Analysis, 1999-2024.

Abstract

Protozoan pathogens are significant contributors to global diarrheal morbidity and mortality, particularly in resource-limited settings. Despite their clinical importance, the global burden and geographic distribution of protozoan-related diarrhea remain incompletely characterized. This study aimed to quantify the prevalence and regional trends of key protozoan pathogens in diarrheal cases globally from 1999 to 2024. A comprehensive systematic review and meta-analysis were conducted following PRISMA guidelines. Five databases (PubMed, Scopus, Google Scholar, Web of Science, and ScienceDirect) were searched for studies reporting the prevalence of <i>Giardia duodenalis, Entamoeba histolytica, Cryptosporidium</i> spp., <i>Blastocystis hominis,</i> and <i>Cyclospora cayetanensis</i> in patients with diarrhea. Random-effects models were used to estimate pooled prevalence, with subgroup analyses by region, age, diagnostic method, and socioeconomic indicators. Heterogeneity and publication bias were assessed using meta-regression and funnel plots. Results of the meta-analysis of 73 studies revealed a global protozoan prevalence of 7.5% (95% CI: 5.6%-10.0%) in diarrheal cases, with the highest rates in the Americas and Africa. <i>Giardia</i> and <i>Cryptosporidium</i> were the most common pathogens. Despite substantial heterogeneity and some small-study bias, findings were robust, with minimal publication bias and variation due to diagnostic methods used. Protozoan pathogens remain major yet underrecognized drivers of diarrheal disease worldwide. Targeted interventions, including improved diagnostics, sanitation, and surveillance, are essential to mitigate their impact.