Table 5.

Metagenomic sequencing studies gut.

Study ID	# of Patients	# of Healthy Controls	Sample Type	16S Region	α–Diversity	β–Diversity	Major Findings	NOS
Lam 2021 [11]	17	20	stool	V3–V4	no significant differences	no significant differences	Robinsoniella peoriensis in HS patients; Sellimonas ↑; Christensenellaceae ↓	4
S. Kam 2020 [36]	3	3	fecal samples from the central portion of the specimen	ND	no significant differences (measured with operational taxonomic unit (OUT)); significant difference: greater in the control group (measured with Shannon index)	no significant differences (measured with weighted UniFrac distance matrices)	HS patients: Firmicutes ↓ Bilophila + Holdemania ↑ Lachnobacterium + Veillonella ↓	8
Eppinga H 2016 [13]	HS only = 17 concomitant HS and IBD = 17	33	20 mg of feces	ND	no significant difference	NC	F. prausnitzii ↓ patients with IBD + HS; no significant difference between the abundance of E. coli and HS cohorts and healthy controls	8
McCarthy 2022 [12]	59	30	fecal	ND	significantly ↓ in HS	less clustering within the HS samples	Ruminococcus callidus + Eubacterium rectale ↑ in HS; the greatest amplicon sequence variants (ASVs) assigned to the taxa Streptococcus spp. and Ruminococcus gnavus	9
Ring 2019 [20]	32	ND	skin covering tunnels	V3–V4 + V3–V4 18S rDNA	ND	ND	Porphyromonas spp. and Prevotella spp. ↑ gelatinous material in the HS tracts; Corynebacterium, Staphylococcus, and Peptoniphilus ↑	3

ND—not determined, NC—not clear.