Group B streptococcus colonisation in pregnant women at Dr. George Mukhari Hospital, South Africa

M C Monyama,S L Lebelo,R T Mavenyengwa,M O Chukwu,J Y Bolukaoto,M Nchabeleng,S R Moyo,M R.B Maloba

doi:10.4102/sajid.v31i3.81

Abstract

The aim of the study was to estimate group B streptococcus (GBS) colonisation in pregnant mothers using selective enrichment broth and solid media for culturing GBS. Vaginal and rectal swabs were collected from 413 pregnant women for GBS culture at recruitment stage. Direct plating and enrichment broth culture methods were compared by using the same swab samples. The swabs were cultured on colistin nalidixic agar (CNA) plate and incubated at 37°C and examined after 18-24 h. The samples which were culture negative on a CNA agar plate were then inoculated into a Todd-Hewitt enrichment broth to recover any GBS present that was not recovered on the solid agar. With the CNA agar plate, the samples were cultured separately to enable identification of colonised sites such as vaginal sites or rectal sites. Rectal and vaginal swabs were inoculated into Todd-Hewitt enrichment broth at the same time in the same tube. The GBS colonisation rate in pregnant women was 30.9% (128/413). The CNA agar plate recovered 45.3% (58/128) of the GBS isolates, whereas 54.7% (70/128) isolates were recovered from Todd-Hewitt broth. Pregnant women of various ages were found to be at risk of GBS colonisation. The colonisation rate was however highest among women of 25–29 age groups as compared with other age groups. Detection of group B streptococcus improved when both rectal and vaginal swabs were collected for laboratory analysis. The simultaneous use of Todd-Hewitt broth and CNA plate also improved the yield of group B streptococcus.

Highlights

Streptococcus agalactiae (Group B streptococcus; group B streptococcus (GBS)) is an encapsulated organism capable of infecting newborn babies, and can produce severe disease in immunocompromised hosts.[1]
GBS colonisation was detected in 30.9% (128/413) of the pregnant women
Group B streptococcus is prevalent worldwide and its colonisation rate varies depending on geographical areas and sociodemographic factors

Summary

Introduction

Streptococcus agalactiae (Group B streptococcus; GBS) is an encapsulated organism capable of infecting newborn babies, and can produce severe disease in immunocompromised hosts.[1] Infection is rare in immunocompetent patients except among those with underlying conditions.[2] The major colonised sites for GBS are reported to be the vagina and the rectum. The colonisation of these regions is a risk factor for subsequent infection in pregnant women and newborns.[3,4] Ethnicity, maternal age, parity, marital status, education and smoking have been reported not to influence the prevalence of colonisation of GBS.[5]. The high incidence might be attributed to the prevalence of HIV as an underlying condition predisposing patients to GBS infection

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