Table 2.

Dysbiosis of the gut microbiota and its interrelationship with LC.

Reference	Patients COVID-19/LC	Measured Parameters				Conclusions
		Fecal Samples	Respiratory Tract Samples	Increased Opportunistic Pathogens	Reduced Microbial Biodiversity
[92] Liu, Q. et al., 2022; https://doi.org/10.1136/gutjnl-2021-325989	G1: 106 patients with LC. G2: 68 non-COVID-19 patients	258 stool samples	-	Yes	Yes	Evidence of gut microbiome composition changes in LC. Could its modulation be useful in LC recovery?
[93] Mazzarelli, A. et al., 2022; https://doi.org/10.3389/fmicb.2022.1049215	97 patients—SARS-CoV-2 infection	97 rectal swabs	-	Yes	Yes	The gut microbiota profile varies with the severity of the SARS-CoV-2 infection and may be a prognostic biomarker.
[96] Gao, F. et al., 2022; https://doi.org/10.1016/j.jad.2022.02.024	G1 = 71 FHW-treated patients with COVID-19. G2 = 104 SHWs who treated non-infected patients with COVID-19.	Bacterial genomic DNA was extracted and analyzed.	-	Yes	Yes	Stress-triggered intestinal dysbiosis in FHWs was persistent for at least 6 months. Neuropsychiatric symptoms in FHWs were correlated directly with the intestinal microbiome.
[97] Vestad, B. et al., 2022; https://doi.org/10.1111/joim.13458	Randomized trial of 181 patients with COVID-19, divided into 3 subgroups.	S1 = Rectal swab material and 16S rRNA gene sequencing. S2 = lung function tests. S3 = rectal swabs and pulmonary function tests.	Pulmonary function tests.	Yes	Yes	Respiratory dysfunction in LC could be correlated with an altered gut microbiome and elevated LBP levels. Possible involvement of the gut–lung axis in LC.
[98] Liu, Q. et al., 2022; https://doi.org/10.1038/s41467-022-34535-8	Cross-sectional and prospective study on a cohort of 133 COVID-19 patients followed for up to 6 months.	Integrated analysis: 296 fecal metagenomes. 79 fecal metabolomics. 1378 viral loads in respiratory tract samples.	Viral load in 1378 respiratory tract samples (sputum and nasopharyngeal sample).	Yes	Yes	Host phenotype and multikingdom microbiota profile could be prognostic factors for COVID-19.
[99] Tkacheva, O.N. et al., 2023; https://doi.org/10.3390/microorganisms11041036	178 patients with post-COVID-19 and contacts for SARS-CoV-2 but without infection.	Fecal samples	-	Yes	Yes	Three months after infection with SARS-CoV-2, the intestinal microbiota was restored, and no significant differences in its composition were found. Novel strategies for microbiome-tailored disease prevention and treatment are needed.
[100] Caio R. et al., 2023; https://doi.org/10.26355/mhd_20233_818	46 patients aged between 30 and 95, hospitalized with COVID-19, were grouped by clinical severity (i.e., non-critical or critical), type of hospitalization (non-intensive care or intensive therapy unit), and outcome.	Stool samples were analyzed by shotgun metagenomic sequencing.	-	Yes	Yes	Intestinal dysbiosis could underlie disease severity, persistent inflammation, and late complications in LC.
[101] Zhang, D. et al., 2023; https://doi.org/10.3346/jkms.2023.38.e120	187 RPs, among them, 84 (44.9%) reported LC one year after discharge.	In 130 RPs and 32 HCs: Stool samples collection and 16s rRNA sequencing.	-	Yes	Significantly reduced bacterial diversities and a lower relative abundance of SCFAs.	SCFAs and SCFA-producing commensal bacteria may delay recovery and sustain the persistence of LC.
[102] Zhang, D. et al., 2023; https://doi.org/10.1186/s12916-023-02972-x	Prospectively analyzed oral, fecal, and serum samples from 983 antibiotic-naïve subjects with mild COVID-19 were monitored for 3 months after discharge.	45 fecal and saliva samples and 25 matched serum samples were collected from patients who had LC with digestive symptoms, compared to HCs.	8 saliva and fecal samples were collected from patients with LC but without digestive symptoms.	Yes	Yes	Patients with digestive symptoms of LC after mild forms of COVID-19 may have an ectopic colonization of the oral microbiome with gut microbes and a disturbance of serum metabolites.