Gastrointestinal microbiota: A predictor of COVID-19 severity?

Table 1 Variants of concern reported for coronavirus disease 2019

VOCs	First time reported	Country of origin
Alpha (B.1.1.7)	December 2020	United Kingdom
Beta (B.1.351)	December 2020	South Africa
Gamma (P.1)	January 2021	Brazil
Delta (B.1.617.2)	December 2020	India
Omicron (B.1.1.529)	November 2021	South Africa

VOC: Variants of concern.

Table 2 Changes in gut and airway microbiota bacterial species during coronavirus disease 2019

Changes	COVID-19 vs non-COVID-19 patients	Number of patients COVID-19 vs non-COVID-19	Ref.
Gut microbiota	Increase: Ruminococcus gnavus, Ruminococcus torque, Bacteroides dorei	100 vs 78	[20]
	Decrease: Bifidobacterium adolescentis, Faecalibacterium prausnitzii, Eubacterium rectale
	Increase: Streptococcus, Rothia, Veillonella, Actinomyces	30 vs 30	[80]
	Increase: Blautia, Coprococcus, Collinsella	53 vs 76	[81]
	Decrease: Streptococcus, Weissella, Enterococcus, Rothia, Lactobacillus, Actinomyces
	Increase: Bifidobacterium, Bacteroides, Parabacteroides, Escherichia-Shigella	22 vs 40	[82]
	Decrease: Faecalibacterium, Dorea, Enterobacter
	Increase: Corynebacterium, Campylobacter, Klebsiella	50 vs 34	[83]
	Increase: Streptococcus, Clostridium, Lactobacillus, Bifidobacterium	64 vs 40	[84]
	Decrease: Bacteroidetes, Roseburia, Faecalibacterium, Coprococcus, Parabacteroides
Airway microbiota	Increase: Veillonella, Staphylococcus, Corynebacterium, Neisseria, Actinobacillus, Selenomonas	192 vs 95	[85]
	Decrease: Haemophilus, Alloiococcus
	Increase: Lactobacillus fermentum, Lactobacillus reuteri, Lactobacillus delbrueckii, Lactobacillus salivarius	19 vs 23	[86]
	Increase: Corynebacterium_1, Staphylococcus, Dolosigranulum, Peptoniphilus, Lawsonella	38 vs 21	[87]
	Decrease: Leptotrichia, Fusobacterium (especially Fusobacterium periodonticum), Haemophilus	18 vs 12	[88]
	Increase: Propionibacteriaceae	31 vs 9	[89]
	Decrease: Corynebacterium accolens

COVID-19: Coronavirus disease 2019.

Table 3 Biomarkers associated with coronavirus disease 2019

Decreased levels	Increased levels
Lymphocytes	White blood cells
Platelets	D-dimers
Eosinophils	Fibrinogen
	C-reactive protein
	Procalcitonin
	Lactate dehydrogenase
	Ferritin
	IL-6
	ALT, AST
	Alkaline phosphatase
	Total bilirubin

ALT: Alanine aminotransferase; AST: Aspartate aminotransferase; IL-6: Interleukin 6.

Table 4 Nutraceuticals used to improve disease severity and outcomes of coronavirus disease 2019 patients

Nutraceuticals	Number of patients with vs without nutraceutical agent	Results	Ref.
Probiotic combined Bifidobacterium, Lactobacillus and Enterococcus	179 vs 196	Shorter time to clinical improvement (fever, hospital stay, viral shedding) in hospitalized COVID-19 subjects	[153]
Probiotic Lactobacillus hamnosus GG	566 vs 566	Extended time until the development of infection with COVID-19, reduced the severity of the disease, changed the composition of the intestinal microbiota in the household contact infected with COVID-19 (after 28 d)	[154]
Probiotic Lacticaseibacillus rhamnosus, Bifidobacterium bifidum, Bifidobacterium longum subsp. infantis, Bifidobacterium longum subsp. longum	99 vs 101	The duration of diarrhea was shorter in patients who received the probiotic than in those who did not. No significant effect on mortality, no change in most biomarkers in patients with COVID-19 in hospitalized patients (at 14 d)	[155]
Vitamin D3 (single oral bolus of 80000 IU)	57 vs 9	The severity of COVID-19 decreased. Improved survival rate	[156]
25-hydroxyvitamin D3	50 vs 26	Reduced the need for treatment in the ICU in patients hospitalized due to proven COVID-19	[157]
Quercetin	21 vs 21	Decreased virus clearance, frequency of symptoms and level of LDH and ferritin parameters	[158]

ICU: Intensive care unit; LDH: Lactate dehydrogenase; COVID-19: Coronavirus disease 2019.