Table 1.

Metadata of samples included in the meta-analysis.

Study (PMID)	Bioproject	Number of samples	Age (days) (mean ± st.dev)	Age (months) (mean ± st.dev)	Nation	Settlement	Socioeconomic status	Technology	Primer region
24896187	PRJEB5482	190	258 ± 233	8 ± 8	Bangladesh	Urban slum	low socioeconomic status	Illumina MiSeq	V1-V2
27160322	PRJNA318053	15	442 ± 262	15 ± 9	Ireland	Urban area	–	Illumina_MiSeq	V4–V5
27306664	PRJEB14529	225	246 ± 207	8 ± 7	USA	Urban area	–	Illumina MiSeq	V4
27717398	PRJNA331150	50	322 ± 104	11 ± 3	USA	Urban area	–	Illumina MiSeq	V4
28079170	PRJEB15633	18	115 ± 34	4 ± 1	Gambia	Urban area	–	Illumina_MiSeq	V4
28095889	PRJNA339264	167	8 ± 38	0 ± 0	Ireland	Urban area	–	Illumina MiSeq	V4–V5
28733284	PRJNA377056	9	383 ± 3	12 ± 0	Italy	Urban area	middle socioeconomic status	Illumina_MiSeq	V3-V4
28789705	PRJNA362530	10	28 ± 6	1 ± 0	Spain	Urban area	–	Illumina_MiSeq	V3
28877893	PRJEB21196	64	118 ± 51	4 ± 2	Germany	Urban area	–	Illumina_MiSeq	V3-V4
29184093	PRJNA403824	47	25 ± 31	1 ± 1	Canada	Urban area	–	Illumina MiSeq	V3
29217369	PRJEB21946	44	70 ± 0	2 ± 0	India	Densely populated Urban area	–	Illumina MiSeq	V4
29795809	PRJEB11419	127	646 ± 266	22 ± 9	USA Thailand United Kingdom Australia Ireland Norway Slovakia Canada	Urban area	–	Illumina MiSeq	V4
29884786	PRJNA450946 PRJNA450998 PRJNA451090 PRJNA451108 PRJNA451156 PRJNA451314 PRJNA451320 PRJNA451359 PRJNA451398 PRJNA451432 PRJNA453125 PRJNA451346	24	186 ± 182	6 ± 6	Norway	Urban area	–	Illumina HiSeq 2500	V4
30131575	PRJNA350676	20	387 ± 0	13 ± 0	Italy	Urban area	–	Illumina MiSeq	V3-V4
30579350	PRJNA491825	25	806 ± 215	27 ± 7	Denmark	Urban area	–	Illumina MiSeq	V3-V4