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GBS screening: An update on guidelines and methods
Abstract
Great advances have been made in preventing neonatal GBS sepsis of both early and late onset. despite recommendations, however, screening is not universal or uniform.
... Owing to the high prevalence of GBS colonization, the paucity of data regarding the safety of membrane stripping in GBS carriers hinders a significant proportion of obstetrical patients from receiving optimal obstetric care. A critical component of appraising the safety of this intervention in these patients is determining whether it hastens labor in a manner that compromises the adequacy of antibiotic prophylaxis, which must be administered no less than 4 h before delivery (6,7,32,33). A study performed by Van Dyke et al. (6) demonstrated that a substantial majority of GBS carriers received adequate prophylactic treatment during labor, though the study did not distinguish between those who underwent membrane sweeping and those who did not. ...
... The adequacy of antibiotic prophylaxis was ascertained based on the administration of beta-lactam antibiotics for a minimum of 4 h before delivery (34). Conversely, insufficient antibiotic prophylaxis was defined as the administration of antibiotics for less than 4 h prior to delivery, following established guidelines (7,32,33). The secondary outcome measures included neonatal morbidities, including birthweight Apgar scores ≤7, days in NICU, and incidence of early or late-onset neonatal GBS disease. ...
Objective
Membrane stripping in group B streptococcus (GBS) carriers poses an increased risk of inadequate antibiotic prophylaxis, potentially due to accelerated labor, thereby potentially impacting the management of GBS colonization during delivery. We compared the adequacy of intrapartum antibiotic prophylaxis between pregnant women colonized with GBS, who underwent membrane stripping and those who did not. The study aimed to determine whether the performance of membrane stripping, by potentially shortening labor duration, increases the risk of inadequate antibiotic prophylaxis dispensation.
Study design
A retrospective cohort study was conducted on GBS screen-positive women with a full-term singleton pregnancy in cephalic presentation, who were eligible for vaginal delivery. The exposed group consisted of women who underwent membrane stripping, while the unexposed group consisted of women who did not undergo membrane stripping. The primary outcome was defined as inadequate duration of antibiotic prophylaxis during labor, wherein less than 4 h of beta-lactam antibiotics were administered prior to delivery. Neonatal outcome was compared between the groups.
Results
This retrospective cohort study comprised 1,609 women, with 129 in the exposed group (stripping group) and 1,480 in the unexposed group (no stripping group). Adequate intrapartum antibiotic prophylaxis was received by 64.3% (83/129) of the exposed group, compared to 46.9% (694/1,480) of the unexposed group (p = 0.003). Membrane stripping was associated with increased odds of receiving adequate prophylaxis (OR 1.897, 95% CI 1.185–3.037, p = 0.008). After excluding women who presented to the labor ward in active labor and delivered in less than 4 h, both the exposed and unexposed groups had similarly high rates of adequate intrapartum antibiotic prophylaxis (87.5% vs. 85.8%, respectively). No significant difference was observed in adverse neonatal outcomes between the groups.
Conclusion
The provision of membrane stripping did not impede adequate intrapartum antibiotic prophylaxis and was correlated with a higher rate of sufficient prophylaxis in comparison to non-swept patients. These observations suggest that membrane stripping can be considered a safe option for ensuring adequate antibiotic prophylaxis in women colonized with GBS.
... Additionally, GBS has the ability to use intracellular survival as a mechanism to evade antibiotics and persistently colonize women, providing a possible explanation for the unchanged rate of late onset neonatal infections despite the implementation of IAP preventative measures. 40 ...
Group B Streptococcus (GBS), a leading cause of neonatal sepsis and meningitis, asymptomatically colonizes up to 30% of women and can persistently colonize even after antibiotic treatment. Previous studies have shown that GBS resides inside macrophages, but the mechanism by which it survives remains unknown. Here, we examined the ability of four GBS strains to survive inside macrophages and then focused on two strains belonging to sequence type (ST)-17 and ST-12, to examine persistence in the presence of antibiotics. A multiple stress medium was also developed using several stressors found in the phagosome to assess the ability of 30 GBS strains to withstand phagosomal stress. The ST-17 strain was more readily phagocytosed and survived intracellularly longer than the ST-12 strain, but the ST-12 strain was tolerant to ampicillin unlike the ST-17 strain. Exposure to sub-inhibitory concentrations of ampicillin and erythromycin increased the level of phagocytosis of the ST-17 strain, but had no effect on the ST-12 strain. In addition, blocking acidification of the phagosome decreased the survival of the ST-17 strain indicating a pH-dependent survival mechanism for the ST-17 strain. Congruent with the macrophage experiments, the ST-17 strain had a higher survival rate in the multiple stress medium than the ST-12 strain, and overall, serotype III isolates survived significantly better than other serotypes. These results indicate that diverse GBS strains may use differing mechanisms to persist and that serotype III strains are better able to survive specific stressors inside the phagosome relative to other serotypes.
... This type of testing requires the same swabs without the incubation time, therefore allowing quicker results. The testing takes less than 30 min for results and has greater than 90% accuracy (Ahmadzia, Heine, & Brown, 2013). Although this method seems ideal, the issue revolves around the cost. ...
Throughout pregnancy women are offered a variety of screenings and diagnostic procedures. Group B Streptococcus (GBS) screening is currently a routine screening process in Australia, but not in the United Kingdom (UK), and which is offered to women at 35-37 weeks gestation. The results of GBS screening alter a woman’s course of care for labour and the postnatal period. This paper is a review of evidence, policy and clinical practice, and aims to determine whether GBS screening is necessary and whether the screening has a positive or negative impact upon women and their babies.
A selective medium containing Todd-Hewitt broth, sheep blood, nalidixic acid, and gentamicin sulfate was found to enhance significantly the isolation of group B streptococci from vaginal cultures. Preparation of the medium, which is stable for up to 4 weeks at 4 C, is simple and inexpensive. Use of such a medium should facilitate identification of vaginal colonization with group B streptococci.
Current prevention of infection due to group B Streptococcus (GBS) involves giving intrapartum antibiotics to women on the basis of either antenatal culture colonization status or presence of risk factors.
We prospectively compared the performance characteristics of a rapid molecular diagnostic test (IDI-Strep B; Infectio Diagnostic) with culture for intrapartum GBS detection after 36 weeks' gestation in 5 North American centers during the period September 2001-May 2002. Antenatal GBS screening was done according to the usual practice of participating hospitals. Two combined vaginal/anal specimens were obtained from participants during labor by use of standard techniques and processed by the same laboratories that processed the antenatal specimens. Each swab sample was processed simultaneously by culture and with IDI-Strep B. The collected specimens were randomized for order of testing of the swab samples by culture or the rapid test.
Of enrolled women, 803 (91.1%) were eligible for analysis. The overall intrapartum GBS colonization rate by culture was 18.6% (range, 9.1%-28.7%). Compared with intrapartum culture, the molecular test had a sensitivity of 94.0% (range, 90.1%-97.8%), specificity of 95.9% (range, 94.3%-97.4%), positive predictive value of 83.8% (range, 78.2%-89.4%), and negative predictive value of 98.6% (range, 97.7%-99.5%). The molecular test was superior to antenatal cultures (sensitivity, 94% vs. 54%; P<.0001) and prediction of intrapartum status on the basis of risk factors (sensitivity, 94% vs. 42%; P<.0001).
Use of this test for determination of GBS colonization during labor is highly sensitive and specific and may lead to a further reduction in rates of neonatal GBS disease.
To estimate the clinical performance characteristics of a real-time polymerase chain reaction (PCR) assay using vaginal/rectal swabs from antepartum (35-37 weeks of gestation) and intrapartum women.
The assay evaluated is a qualitative, automated, real-time PCR test for the detection of group B streptococci, with results available in approximately 75 minutes. Enrollment in this multicenter clinical study occurred between October 2005 and January 2006. Vaginal/rectal swabs were analyzed by nursing personnel (intrapartum tests) or by laboratory technologists (all others). Polymerase chain reaction assay results were compared with culture using standard methods, including selective broth medium, and to a predicate nucleic acid amplification test.
Of 1,028 enrolled women, 234 were deemed ineligible, and 10 had unresolved test results. Of the 784 remaining women, valid PCR assay results were obtained on the first test attempt for 93.0%. Performance characteristics relative to culture were sensitivity 91.1%, specificity 96.0%, positive predictive value 87.8%, negative predictive value 97.1%, and accuracy 94.8%. These results exceeded those obtained using the predicate nucleic acid amplification test.
Performance characteristics of the PCR assay exceed the threshold recommended by the Centers for Disease Control and Prevention when compared with culture. The test is sufficiently robust to be performed for intrapartum patients in a point-of-care setting by medical professionals.
II.
To evaluate the sensitivity, specificity, and feasibility of a rapid real-time polymerase chain reaction (PCR) test for group B streptococcus (GBS) completed during labour, compared with the standard culture test performed at 35 to 37 weeks' gestation.
Women presenting to the maternity unit for term vaginal delivery had two vaginal/rectal samples collected. One swab was tested using a rapid PCR method (IDI-Strep B, Infectio Diagnostic [IDI] Inc., Sainte-Foy QC ), and the other was cultured after enrichment (intrapartum culture). Comparisons were made between these results and those of a culture-based screen at 35 to 37 weeks' gestation.
Of the 190 women enrolled, 85% had results of the standard screen at 35 to 37 weeks available for comparison. The sensitivity and specificity of the standard 35- to 37-week screen were 84.3% (95% confidence interval [CI], 71.4-93.0) and 93.2% (95% CI 86.5-97.2) respectively, whereas the sensitivity and specificity of the rapid PCR were 90.7% (95% CI 79.7-96.9) and 97.6% (95% CI 93.1-99.5), respectively. The median reporting time for the rapid PCR test was 99 minutes (range 50-255). Results were available more than four hours before delivery in 81% of cases.
In this Canadian centre, a rapid PCR test done at the time of labour (IDI-Strep B) demonstrated high sensitivity and specificity, comparable to the 35- to 37-week screen. The time to reporting results was acceptably short, allowing for timely administration of intrapartum prophylactic antibiotics.
To investigate whether specimens obtained from the perianal area have a Group B streptococcal culture detection rate similar to anorectal specimens.
This is a prospective cohort study at a tertiary care university-affiliated teaching hospital. A total of 136 pregnant women between 33 and 40 weeks' gestation were recruited. Three samples for Group B streptococcal culture detection were obtained from each subject in the following order: perianal sample, vaginoperianal sample, and an anorectal sample. The women were asked to rank their pain or discomfort with obtaining the anorectal sample. The vaginoperianal specimen is the standard sample obtained from antepartum patients in this clinic, and, therefore, it serves as the control.
Of the 136 subjects, 26.5% of the control, vaginoperianal samples were positive for Group B streptococcal culture. In comparison, 27.2% of the anorectal specimens and 28.7% of the perianal specimens were positive for Group B streptococcal culture. There was no statistically significant difference in the detection of Group B streptococcal culture among the three sample sites. Evaluation of the pain experienced with an anorectal sampling showed that 68% of subjects ranked their pain between mild to moderate, and 5% noted severe pain.
The Group B streptococcal detection rate was not different among the three sampling sites. Therefore, pregnant women do not need to be subjected to the additional pain of anorectal sampling to detect Group B Streptococcus.
The objective of the study was to evaluate a rapid real-time polymerase chain reaction (PCR)-based assay for intrapartum detection of group B streptococcus (GBS).
This prospective, observational study enrolled outpatients after GBS screening at 35-37 weeks' gestation. At admission for delivery, paired rectovaginal swabs were obtained for the GBS GeneXpert (Cepheid, Sunnyvale, CA) assay and standard culture. Using the intrapartum culture as the gold standard, sensitivities, specificities, and predictive values of the rapid assay and the antenatal screen were determined. Statistical significance was determined by Fisher's exact test.
Fifty-five subjects had both rapid test and intrapartum culture results. The intrapartum GBS colonization rate was 43.6%. The sensitivity and specificity of the PCR test were 95.8% (95% confidence interval [CI], 76.9-99.8%), and 64.5% (95% CI, 45.4-80.2%), respectively, whereas the antenatal culture sensitivity was 83.3% and specificity was 80.6%.
The GeneXpert rapid GBS point-of-care assay was highly sensitive for GBS detection in our sample population. Corroboration of these data is needed on a large population basis.