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Serotype Prevalence of Group B Streptococcus among Pregnant Women in Iran: A Systematic Review and Meta-Analyses from

Maryam Banar¹, Mohammad Emaneini², Fereshteh Jabalameli²

¹Department of Pathobiology, School of Public Health, Tehran University of Medical Sciences, Tehran, Iran.

International Journal of Fertility & Sterility

|January 27, 2026

Insights

Group B Streptococcus (GBS) serotype III is most prevalent in Iranian pregnant women. This finding is crucial for developing effective GBS vaccines to protect newborns from invasive diseases.

Area of Science:

Microbiology
Immunology
Public Health

Background:

Group B Streptococcus (GBS), or *Streptococcus agalactiae*, is a primary cause of invasive neonatal disease.
Maternal recto-vaginal colonization is the main source of GBS transmission to newborns.
GBS capsular polysaccharide serotypes are key virulence factors, with ten identified types (Ia, Ib, II-IX).

Purpose of the Study:

To determine the prevalence of GBS serotypes in pregnant women in Iran.
To provide data essential for the development of GBS vaccines tailored to the Iranian population.

Main Methods:

A systematic literature search was performed across major databases (MEDLINE, Embase, Web of Science, SID, Magiran) for studies from January 2000 to March 2023.
Included studies utilized standardized recto-vaginal specimen collection and GBS identification methods (selective media, molecular detection of *dltS* and *atr* genes).
Meta-analyses were conducted using Comprehensive Meta-Analysis software to estimate GBS serotype prevalence and 95% confidence intervals (CIs).

Main Results:

Fourteen studies, comprising 330 initial articles, met the inclusion criteria.
Over 93% of GBS isolates had identifiable serotypes.
The most prevalent GBS serotype was III (39.6%), followed by II (16.8%), V (14.1%), VI (12.4%), Ia (11.7%), and Ib (11.2%).

Conclusions:

Serotype III is the dominant GBS serotype among pregnant women in Iran, with serotypes II, V, VI, Ia, and Ib also being significant.
These findings support the potential benefit of a pentavalent vaccine targeting these prevalent serotypes to prevent GBS-related complications in Iranian newborns.
Further research is recommended to assess the efficacy and implementation strategies for such a vaccine.

Read full analysis

Abstract

Background:

Group B Streptococcus (GBS; Streptococcus agalactiae) is a significant cause of invasive disease in newborns, often stemming from recto-vaginal colonization in pregnant women. The GBS capsular polysaccharide is a major virulence factor, and ten distinct serotypes (Ia, Ib, II-IX) have now been identified. Understanding the prevalence of these serotypes in maternal colonization is crucial for vaccine development. This study aims to determine the serotype prevalence of GBS among Iranian pregnant women.

Materials And Methods:

A systematic search was conducted in MEDLINE (via PubMed), Embase, Web of Science, and the Iranian Databases (SID and Magiran) for studies published between January 2000 and March 2023. Studies were included if they used standardized methods for GBS detection, including recto-vaginal specimen collection and identification [selective media and molecular detection of GBS-specific gene (dltS and atr)]. Studies using nonstandard methods (e.g., cervical, perianal, perirectal or perineal specimens), or focusing on non-maternal GBS colonization were excluded. Meta-analyses were performed using Comprehensive Meta-Analysis (Biostat V2.2) software to estimate serotype prevalence with 95% confidence intervals (CIs).

Results:

Of 330 articles identified, 14 studies met the inclusion criteria. The meta-analyses showed that 93.2% (95% CI: 90-95.5) of GBS isolates had identifiable serotypes. The predominant serotype was serotype III [39.6% (95% CI: 31.6-48.2)], followed by serotypes II [16.8% (95% CI: 13.8-20.4)], V [14.1% (95% CI: 11.2-17.6)], VI [12.4 (95% CI: 8.2-18.5)], Ia [11.7% (95 CI: 7.8-17.2)] and Ib [11.2 (95% CI: 6.9-17.6)].

Conclusion:

Serotype III is the most common GBS serotype among pregnant women in Iran, followed by serotypes II, V, VI, Ia, and Ib. These findings suggest that a pentavalent vaccine targeting these serotypes could be beneficial for preventing GBS-related complications in Iranian pregnant women. However, further research is needed to evaluate the efficacy and implementation of such a vaccine.

Keywords:

Group B Streptococcus Iran Pregnant Women Serotype Systematic Review

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