Table 1.

Studies on association of microbiota with COVID-19 patients

Sl. no.	Author, Year, place	Study title	Objectives	Method	Key Findings
1.	Gu S, et al., (2020), China (50)	Alterations of the gut microbiota in patients with COVID-19 or H1N1 influenza	To study the gut microbial flora in COVID-19, H1N1 patients and healthy individuals	Prospective cohort study (n = 84)	Gut microbiome of COVID-19 and H1N1 patients were significantly different from healthy individuals. An abundance of opportunistic pathogens and relatively lower beneficial symbionts were observed in COVID-19 patients. H1N1 patients had a lower diversity and overall different microbial composition.
2.	Zuo T, et al., (2020), Hong Kong (40)	Alterations in gut microbiota of patients with COVID-19 during time of hospitalization	To investigate faecal microbiome in hospitalised COVID-19 patients	Prospective cohort study (n = 15)	Significant alteration in gut microbiome was seen in COVID-19 patients. Baseline microbial composition correlated with COVID-19 severity. This dysbiosis persisted even after the symptoms resolved and virus had cleared.
3.	Gou W, et al., (2020), China (49)	Gut microbiota may underlie the predisposition of healthy individuals to COVID-19	To identify proteomic biomarkers that may indicate predisposition to COVID-19 in healthy individuals To assess influence of gut microbiota on these biomarkers in healthy individuals	Multi-methodological study	Identified 20 blood proteomic biomarkers and drafted a proteomic risk score that could predict severity of COVID-19 in patients Gut microbial features were predictive of blood proteomic markers indicating a potential biological mechanism on disease predisposition.
4.	Liu F, et al., (2021), China (41)	Gastrointestinal disturbance and effect of fecal microbiota transplantation in discharged COVID-19 patients	To study the effect of fecal microbiota transplantation in GI disturbances, gut microbiota and immune system after SARS-CoV-2 infection	Prospective interventional study (n = 11)	Gut dysbiosis was observed in patients after SARS-CoV-2 infection. Fecal microbiota transplantation attenuated GI symptoms, partially restored gut microbiome, and significantly altered B lymphocytes.
5.	Yeoh YK, et al., (2021), Hong Kong (42)	Gut microbiota composition reflects disease severity and dysfunctional immune responses in patients with COVID-19	To assess the association between gut microbiota and COVID-19 patients	Prospective cohort study (n = 165)	Significant alteration in the gut microbiome was observed in COVID 19 patients, associated with disease severity and plasma concentrations of several chemokines, cytokines, and inflammatory markers Significant decrease in gut microbes with immunomodulatory properties were seen in COVID 19 patients.