Gut Microbiome Dysbiosis in COVID-19: A Systematic Review and Meta-Analysis of Diversity Indices, Taxa Alterations, and Mortality Risk.

COVID-19 is associated with gut microbiome alterations that may influence disease outcomes through immune and inflammatory pathways. This systematic review and meta-analysis evaluated global evidence on gut dysbiosis in COVID-19. We searched PubMed/MEDLINE, Embase, Web of Science, Scopus, and Cochrane Library up to 5 October 2025 (PROSPERO CRD420251160970). Alpha-diversity indices and microbial taxa log-fold changes (logFC) were analyzed using random-effects models. The pooled standardized mean difference (SMD) for the Shannon index was -0.69 (95% CI -0.84 to -0.54; I2 = 42%), confirming reduced microbial diversity. Faecalibacterium prausnitzii showed a significant pooled depletion (logFC = -1.24; 95% CI -1.68 to -0.80; k = 10; I2 = 74%), while Enterococcus spp. was increased (logFC = 1.45; 95% CI 1.12-1.78). Egger's test did not suggest publication bias (p = 0.32). Gut dysbiosis was consistently associated with reduced microbial diversity and enrichment of pathogenic taxa, correlating with increased disease severity and mortality (HR = 1.67). These findings highlight the potential of microbiome profiling as a prognostic tool in COVID-19, although clinical translation requires further validation.