Neonatal group B streptococcal disease

Evaluation of an in-house real-time polymerase chain reaction method to identify group B streptococcus colonization in pregnancy

AIM

The aim of this study was to evaluate the performance of in-house real-time polymerase chain reaction (qPCR) in detecting group B streptococcus (GBS) colonization compared with the standard culture method in a cohort of pregnant women.

MATERIAL AND METHODS

A total of 134 rectovaginal swabs were collected from 125 pregnant women, of whom 108 were known carriers or presented with preterm prelabor rupture of membranes. The swabs were placed in Standard Methods Broth (Todd-Hewitt broth supplemented with 6 μg/mL gentamicin and 15 μg/mL nalidixic acid) for culture identification of GBS. An in-house qPCR was also performed from the broth and after overnight incubation of the broth.

RESULTS

The detection rate of GBS in this cohort was 30.6% and 50.7% using standard culture method and qPCR, respectively. GBS-specific qPCR assay gave sensitivities of 97.6% and 100%, specificities of 73.1% and 71.0%, and negative predictive values of 98.6% and 100% from direct specimen and from broth after overnight incubation, respectively.

CONCLUSIONS

The in-house qPCR test has high sensitivity in detecting GBS colonization. The high negative predictive value helps to avoid unnecessary use of antibiotics in uncolonized women.

Carriage of group B streptococcus in pregnant women from Oxford, UK

OBJECTIVE

To investigate asymptomatic vagino-rectal carriage of group B streptococcus (GBS) in pregnant women.

METHODS

Women in the final trimester of pregnancy were recruited. A single vagino-rectal swab was taken, with consent, for culture of GBS. Two microbiological methods for isolation of GBS from vagino-rectal swabs were compared. The distribution of capsular serotypes of the GBS identified was determined. Epidemiological data for a subset (n = 167) of the pregnant women participating were examined.

RESULTS

21.3% were colonised vagino-rectally with GBS. Risk factors for neonatal GBS disease (maternal fever, prolonged rupture of membranes, and preterm delivery) were present in 34 of 167 women (20.4%), and the presence of these factors correlated poorly with GBS carriage. Capsular serotypes III (26.4%), IA (25.8%), V (18.9%), and IB (15.7%) were prevalent in the GBS isolates. Selective broth culture of vagino-rectal swabs was superior to selective plate culture, but the combination of both methods was associated with increased detection of GBS (7.5%). An algorithm for the identification of GBS from vagino-rectal swabs was developed.

CONCLUSIONS

GBS carriage is prevalent in pregnant women in Oxfordshire, UK. The poor correlation between risk factors and GBS carriage requires further investigation in larger groups, given that the identification of these surrogate markers is recommended to guide administration of intrapartum antibiotic prophylaxis by the Royal College of Obstetricians of the UK. A selective broth culture detected more GBS carriers than a selective plate culture.

Group B streptococci during pregnancy and infancy

Group B streptococcus (Streptococcus agalactiae) is still of great relevance in the perinatal period, although maternal antimicrobial prophylaxis has significantly reduced the rate of culture-confirmed invasive infection in neonates. This strategy, however, raises considerable concern because preterm delivery or late-onset sepsis cannot be prevented, and antibiotic resistance is increasing worldwide. Several advances in the development of conjugate vaccines and in research on virulence factors and pathways involved in the immune response to group B streptococcus have been accomplished, some of which might reach clinical practice in the near future.