Prevalence, risk factors, and serotypes of group B Streptococcus rectovaginal colonization among pregnant women: a cross-sectional study at three hospitals in Hanoi, Vietnam

Abstract

Background: Group B Streptococcus (GBS) infection among pregnant women is a major risk factor for a significant proportion of early-onset disease and late-onset disease in infants worldwide; however, data on the epidemiological features of GBS in Vietnam are very limited.

Objectives: To determine the prevalence, potential risk factors, and serotype distribution of GBS isolates isolated from rectovaginal specimens of Vietnamese pregnant women.

Design: Cross-sectional study.

Methods: A cross-sectional study was conducted at three hospitals in Hanoi City, Vietnam, from October 2021 to May 2022. Combined rectovaginal swabs were collected from pregnant women at 35-37 weeks of gestation. GBS was isolated from swabs using selective enrichment in Todd-Hewitt broth and cultured on Columbia agar plates with 5% sheep blood, and Chromogenic Strepto B. All isolates were confirmed through the Gram staining, the CAMP test, and specific Polymerase Chain Reaction (PCR). GBS serotyping was performed by using the multiplex PCR assays. Risk factors for GBS carriage were analyzed using univariate and multivariate logistic regression tools.

Results: The prevalence of rectovaginal GBS carriage was 19.52% of 876 participants. Multivariate analysis identified two independent risk factors associated with GBS colonization: a high level of education and yellow vaginal discharge. Among these isolates, serotype III (n = 40, 23.39%) was the most frequently found, followed by serotypes V (n = 37, 21.64%), VI (n = 21, 12.28%), Ia (n = 18, 10.53%), Ib (n = 17, 9.95%), II (n = 8, 8.77%), and VII (n = 1, 0.58%), respectively. Capsular types IV, VIII, and IX were not detected. No statistically significant correlation was found between GBS infection and the distribution of the identified serotypes.

Conclusion: The GBS colonization rate in pregnant women was consistent with findings from other studies worldwide. Higher educational attainment and the presence of yellow vaginal discharge were independently associated with an increased risk of GBS colonization. The predominance of GBS serotypes III, V, and VI was a notable feature among the strains isolated from pregnant women in Vietnam.

Keywords: Streptococcus agalactiae; Vietnam; pregnant women; risk factors; serotypes.

Figure 1.

Gel electrophoresis of GBS-specific PCR products targeting the 952bp dltS gene. Lanes 1–10 and 12–13: clinical GBS samples; Land 11: molecular size standard (100 bp DNA ladder); Lane 14: positive control (Streptococcus agalactiae ATCC^® 13813); Land 15: negative control. GBS, Group B Streptococcus.

Figure 2.

Frequency distribution of capsular types among pregnant women.

Figure 3.

The mPCR patterns of serotypes Ia, Ib, II, and III. Lanes 4, 5, and 7 denoted to those of serotype Ia; Lane 12 denoted to those of serotype Ib; Lanes 6 and 9 denoted to those of serotype II; Lanes 2 and 11 denoted to those of serotype III; Lanes 1, 3, and 8 denoted to those of serotypes not belonging to groups I, II, or III. Lane 13: 100 bp DNA ladder (molecular weight marker); Lane 14: positive control (serotype II); Lane 15: negative control. mPCR, multiplex PCR.