Table 1. Summary of included studies.

Author	Study period	Region	Study design	Age range (years)	No of iGBS cases	Incidence (cases per 100.000)	Method for incidence estimation	CFR (%)
Alhhazmi	2003–2013	North America	Population-based surveillance	≥ 15	1372	3.23	Average of incidence by age group provided by article	-
Barnham	1978–1988	Europe	Population-based surveillance	25–86	6	0.24	Estimated from cases per catchment population provided by article	33.0
Bjornsdottir	1975–2014	Europe	Population-based surveillance	19–90	139	2.19	Average of incidence by age group provided by article	-
Blumberg	1992–1993	North America	Population-based surveillance	39.1–75.3	112	5.9	Provided by article	-
Bolaños	1992–1999	Europe	Population-based surveillance	21–100	32	1.5	Provided by article	31.0
Bunyasontigul	1999–2009	Asia	Retrospective cohort study	15.3–91.6	101	-	-	7.9
Camuset	2011	Africa	Prospective hospital-based study	25–93	22	10.1	Provided by article	4.5
Collin	2015–2016	Europe	Population-based surveillance	≥ 15	2225 (episodes)	2.9	Provided by article	12.5
Cooper	1991–1996	North America	Retrospective hospital-based study	“adults”	55	-	-	16.4
Crespo-Ortiz	2004–2012	South America	Retrospective & cross-sectional study	17–83	57	0.90	Estimated from cases per catchment population provided by article	17.5
Darbar	2000–2005	Australia	Prospective hospital-based study	47.3–78.7	80	-	-	10.0
Farley	1989–1990	North America	Population-based surveillance	18–99	140	4.4	Provided by article	21.0
Francois Watkins	2008–2016	North America	Population-based surveillance	≥ 18	21250	9.5	Average of incidence of surveillance years provided by article	6.5
Fujiya	2002–2014	Asia	Retrospective cohort study	24–91	52	2.5	Provided by article	5.8
Georges	1991–2006	Europe	Population-based surveillance	15–64	-	1.8	Provided by article. Not used for the meta-analysis due to information on denominators not available	-
				>64		4.1(1991) 9.1(2006)
Gimenez	1983–1993	Europe	Retrospective study	40–80	35	0.58	Estimated from cases per catchment population provided by article	8.7
Gudjonsdottir	2004–2009	Europe	Population-based surveillance	23–103	317	3.47	Estimated from cases per catchment population provided by article	12.0
Huang	2001–2003	Asia	Retrospective study	22–89	94	-	-	20.2
Jenkins	2006–2009	Europe	Population-based surveillance	28–84	17	0.69	Provided by article	0.0
Jones	2000–2003	Europe	Prospective hospital-based study	> 60	70	11.0	Estimated from cases per catchment population provided by article	-
Jump	2008–2017	North America	Prospective cohort study	≥ 18	5497	-	-
Kalimuddin	2011–2015	Asia	Retrospective cohort study	Nonpregnant adults	408	-	-	7.4
Lamagni	1991–2010	Europe	Retrospective study	≥ 15	13376	1.66	Average of incidence of surveillance years provided by article	-
Lambertsen	1999–2004	Europe	Population-based surveillance	16–99	411	2.7	Average of incidence of surveillance years provided by article	14.0
Lee	1991–1999	Asia	Prospective hospital-based study	18–85	71	-	-	7.0
Lopardo	1998–1999	South America	Prospective hospital-based study	21–83	31	-	-	12.9
Matsubara	1998–2007	Asia	Retrospective hospital-based study	29–90	52	1.04	Estimated from cases per catchment population provided by article	13.5
Morozumi	2010–2013	Asia	Prospective study	19- >90	443	-	-	10.2
Mosites	2002–2015	North America	Retrospective study	≥ 18	6	-	-	33.0
Perovic	1995–1997	Africa	Retrospective hospital-based study	22–87	40	0.44	Estimated from cases per catchment population provided by article	35.0
Phares	1999–2005	North America	Population-based surveillance	≥ 15	11663	6.95	Average of incidence of surveillance years provided by article	10.3
Ruppen	1998–2015	Europe	Retrospective hospital-based study	≥ 65	171	-	-	5.0
Schrag	1993–1998	North America	Population-based surveillance	≥ 15	5293	11.9α	Average of incidence by age group provided by article	11.5
Schwartz	1982–1983	North America	Retrospective population-based surveillance	≥ 20	56	2.4	Provided by article	-
Shelburne	2000–2011	North America	Retrospective hospital-based study	27–86	147	-	-	6.0
Skoff	2007	North America	Population-based surveillance	18–105	1546	7.3	Provided by article	7.5
Slotved	2005–2018	Europe	Population-based surveillance	20–64	-	1.35	Not used for the meta-analysis. Number of cases by age group not extractable	-
				65–74		5.35
				> 75		9.80
Tyrrell	1996	North America	Population-based surveillance	≥ 15	91	4.1	Provided by article	5.5
Wilder-Smith	1998	Asia	Prospective hospital-based study	24–63	11	1.1	Estimated from cases per catchment population provided by article	9.1

α: Incidence in 2008 only.