COVID-19 and clostridioides difficile infection: clinical overlap, gut dysbiosis, and mechanistic hypotheses

The COVID-19 pandemic, caused by SARS-CoV-2, produced a global health crisis with disproportionate morbidity and mortality among older adults and medically vulnerable populations. Clostridioides difficile infection (CDI), a leading cause of antibiotic-associated diarrhea and health care-associated colitis, affects many of the same populations and is strongly influenced by antimicrobial exposure, hospitalization, immune status, and disruption of colonization resistance. This narrative mini-review synthesizes clinical and mechanistic evidence linking COVID-19, COVID-19-related care pathways, and susceptibility to CDI, while explicitly distinguishing established observations from hypotheses requiring experimental validation. We distinguish simultaneous SARS-CoV-2/CDI co-infection, CDI developing during hospitalization for COVID-19, and delayed or recurrent CDI after recovery from acute SARS-CoV-2 infection. The available evidence suggests that the interaction is multifactorial and may involve broad-spectrum antibiotic exposure, prolonged hospitalization, infection-prevention disruptions during pandemic surges, SARS-CoV-2-associated gut dysbiosis, epithelial barrier dysfunction, altered bile acid metabolism, and persistent inflammatory signaling. Particular emphasis is placed on angiotensin-converting enzyme 2 (ACE2), renin-angiotensin system imbalance, angiotensin II/AT1R signaling, NF-κB/MAPK activation, IL-6 production, nutritional vulnerability, ApoE-related immunometabolic pathways, and emerging extracellular vesicle-based biomarker frameworks as potential mechanistic interactions. Although direct longitudinal evidence remains limited, convergent clinical and experimental findings support a cautious, testable hypothesis that SARS-CoV-2 infection and COVID-19-related treatment pathways may create a biological context permissive to CDI or delayed intestinal recovery in susceptible individuals. Prospective studies with standardized CDI testing, antimicrobial exposure assessment, microbiome and metabolomic profiling, and mechanistic biomarker discovery are needed to clarify risk, prognosis, recurrence, and long-term consequences.