Group B Streptococcus Testing
Group B Streptococcus (GBS) Testing is a medical procedure that screens for the presence of the GBS bacteria in a pregnant woman’s body. It is important for this test to be performed because a GBS infection during pregnancy can cause neonatal meningitis, sepsis, or even death (Albouy-Llaty, Nadeau, Descombes, Pierre & Migeot, 2012). According to Mercer, Ramsey & Sibai (1995), 18 to 32 percent of congenital infections are caused by neonatal sepsis and can be a major cause of mortality and morbidity where 1.3 to 3 per 1000 neonates are affected by the early onset of Group B streptococcal sepsis. Valkenburg-van den Berg et al. (2010) also suggest that GBS disease in neonates is most dangerous during the pre-term period; hence, the need for this test to be performed antenatal. Moreover, it can cause chorioamnionitis or post-partum endometritis in the mother.
Furthermore, its importance is stressed by the effects of GBS colonization among pregnant women. For example, in France, up to 20 percent of women showed positive results for GBS culture (Albouy-Llaty et al., 2012). However, with the increased adoption of GBS screening guidelines in France since 2001, a decrease in the incidence of neonatal GBS infection resulted (Al-bouy-Llaty, 2012). Similarly, Valkenburg-van den Berg et al. (2010) reported that GBS tests and the use of intrapartum prophylactic antibiotics led to a decrease in the incidence of GBS-EOD (Group B Streptococcus-Early Onset Disease) in the 1990s. These attest to the importance of the screening process not only for the mother but also for the child. In addition, this serves as evidence of the effectiveness of the test in the detection of GBS in the woman’s body, which in turn enables treatment to be provided in a timely manner.
With the insensitivity of rapid tests, the lack of an effective anti-GBS vaccine, and the lack of efficacy of antepartum therapy, the use of antepartum culture as a basis for intrapartum treatment has become the main form of preventive measure against the vertical transmission of GBS.
Various physicians have different ways of performing the GBS test. In a study conducted by Mercer and colleagues (1995) regarding the practices of physicians when it comes to performing a GBS test, it was found that 4.8% of the respondents applied the screening swab at the cervix and proximal and distal vagina and anal canal; 9.5% applied it on the cervix and distal vagina; 9.6% applied it on the cervix and proximal and distal vagina; 12.1% applied it on the cervix alone; ; 13.5% on the distal vagina alone; and 15.5% on the distal vagina and anal canal (Mercer et al., 1995). The swabs are then “placed into the same container with Amies medium (Copan, Italy) to be cultured within 36 h in non-enrichment and in selective medium for 48 h at 36 18C. Mueller Hinton agar (Oxoid, Unipath) supplemented with 5% defibrinated sheep blood is employed for antimicrobial susceptibility testing” (Cheng, Shaw, Lin, Huang and Soong, 2006, p. 30). On the other hand, in the study conducted by Hiller, McDonald, Darbyshire, and Crowther (2005, p. 1), the “swabs were cultured on layered horse blood agar and inoculated into selective broth prior to analysis.”
The timeline or frequency for performing the test varies among physicians, too. According to the findings of Mercer and his colleagues (1995), 65.8% of the .physicians performed the test only in high-risk instances. In addition, the Royal College of Obstetricians and Gynecologists stated that routine screening – whether risk based or bacteriological – for antenatal GBS carriage was not recommended (Hiller et al., 2005).
Advice for Women
Minkoff and Mead’s advise (Mercer et al., 1995) was that women who undergo a preterm premature rupture of membranes or a preterm labor must have cultures for GBS performed. They also suggested that undelivered carriers should receive two weeks of anti-microbial therapy and a follow-up evaluation (Mercer et al., 1995). On the other hand, those who were delivered before the culture results became available should receive empiric prophylaxis.
On another perspective, the ACOG (American College of Obstetricians and Gynecologists) suggested the screenings of populations at increased risk for neonatal GBS sepsis, which consisted of those who have undergone surgical surgery in pregnancy, a premature rupture of membranes remote from term, or an arrested or threatened preterm labor (Mercer et al., 1995). The carriers with risk factors for neonatal sepsis should then be provided with intrapartum treatment.
On the other hand, the Centers for Disease Control and Prevention in the United States advised that rectovaginal cultures be performed during the antenatal period at the woman’s 35th to 37th week of gestation. They also advised that pregnant women with positive GBS cultures be provided with IAP (Intrapartum antibiotic prophylaxis) during delivery (Valkenburg-van den Berg et al., 2010). This was based on the findings of Yancey et al. and Boyer et al. (Valkenburg-van den Berg et al., 2010), which indicated that the GBS colonization status at delivery were accurately predicted by cultures when they were obtained in the late antenatal period. This was further affirmed by the findings of Valkenburg-van den Berg et al (2010), which indicated that a GBS test conducted between the 35th and 37th week of gestation would indeed predict GBS colonization at term delivery. Furthermore, even the findings of Hiller et al. (2005) indicated that GBS infection between the 35th and 37th week of gestation had better predictive values and test characteristics than during the 31st to 33rd week, which was the standard protocol at the WCH (Women’s and Children’s Hospital) in Adelaide. Hiller et al.’s (2005) findings also showed that a combination of low vaginal and perianal swabbing did not have any distinct advantage over low vaginal swabbing alone.
However, tests performed between the 35th ad 37th weeks are not as accurate when conducted on the preterm neonatal group where GBS sepsis is most dangerous. As such, various prevention strategies advise the use of antibiotic prophylaxis in cases of pre-term labor where GBS status is unknown. However, large doses of IAP have their side effects, which include a disturbance of both the neonate’s and the mother’s vaginal and intestinal flora and a reduced level of resistance or susceptibility to other microorganisms (Valkenburg-van den Berg et al., 2010).
As such, the advice given in 1992 by the Committee on Infectious Diseases and the Committee on the Fetus and Newborn of the American Academy of Pediatrics (Mercer et al., 1995) may be employed. According to their advice, pregnant women should undergo routine testing from the distal vagina and anorectum during the 26th to 28th weeks of gestation and intrapartum prophylaxis should be given to GBS carriers with risk factors for neonatal sepsis. However, while this can be an effective measure for minimizing IAP while still ensuring the prevention of perinatal GBS infection in pre-term neonates, Valkenburg-van den Berg et al. (2010) advised that cultures should be repeated in the latter part of the pregnancy as the results of early tests are not capable of predicting colonization during delivery after six weeks. In particular, Valkenburg-van den Berg et al. (2010) advised that the repetition of cultures be performed only at the 35th to 37th week of gestation for women who tested positive at the 29th to 31st week of gestation.
In another strategy, all pregnant women in labor and all pregnant women who have risk factors for neonatal sepsis are to be provided with treatment (Mercer et al., 1995).
GBS Testing and Anxiety in Pregnant Women
A study conducted by Cheng et al. (2006) found that women who tested positive of GBS colonization experienced a high level of worry at the time that they received the test result. However, the study showed that this anxiety decreased considerably during the postpartum period. This anxiety may be attributed to the patient’s level of knowledge with regards to the test procedure and with their lack of understanding about the bacterium (Cheng et al., 2006). With the findings of Cheng et al.’s (2006) study, it was shown that women with GBS colonization did not have a sustained increase in anxiety. As such, maternal anxiety should not be an obstacle for GBS testing.
Future Recommendations
For future research, it would be recommended that more studies be conducted with regards to the appropriate timing for performing a GBS test. As it is, different guidelines suggest different times and frequencies as the appropriate timing for performing this test. As a result, even doctors have varying thoughts and practices about this. Even the preferred sites for testing vary, and so a general consensus on the best timing and site for testing should be established. This would ensure the most accurate results for pregnant women regardless of their geographical location. In the same manner, with GBS testing strategies varying in different countries, it would be recommended that integrated obstetrical and neonatal regimens that are appropriate for various populations be established (Seoud et al., 2010). Since practitioners from other countries also adhere to universal guidelines, such guidelines should be made applicable to pregnant women of all nations, with considerations of their ethnicity, culture, and socio-economic situations, which may have an effect on their GBS test results.
As well, despite the clear benefits of undergoing GBS tests, many pregnant women still fail to do so due to their incorrect perceptions about the bacterium, the test, and the results of the test. As such, it is recommended that efforts be made to improve compliance for these tests through patient education, through a dialogue with their physicians, and through physicians serving as advocates for the test.
References
Albouy-Llaty, M., Nadeau, C., Descombes, E., Pierre, F, & Migeot, V. (2012). Improving
perinatal Group B streptococcus screening with process indicators. Journal of Evaluation
in Clinical Practice 18, 727-733.
Cheng, P. J., Shaw, S. W., Lin, P. Y., Huang, S.Y. & Soong, Y. K. (2006).
Maternal anxiety about prenatal screening for group B streptococcus disease and impact
of positive colonization results. European Journal of Obstetrics & Gynecology and
Reproductive Biology, 128, 29-33.
Hiller, J. E., McDonald, H. M., Darbyshire, P. & Crowther, C. A. (2005, July 22). Antenatal
screening for Group B Streptococcus: A diagnostic cohort study. BMC Pregnancy and
Childbirth, 5 (12).
Mercer, B. M., Ramsey, R. D. & Sibai, B. M. (1995). Prenatal screening for Group B
Streptococcus. American Journal of Obstetrics & Gynecology, 173 (3), 837-841.
Seoud, M. et al. (2010). Prenatal and neonatal Group B Streptococcus screening and serotyping
in Lebanon: Incidence and implications. Acta Obstetricia et Gynecologica, 89, 399-403.
Valkenburg-van den Berg, A. W., Houtman-Roelofsen, R. L., Oostvogel, P. M., Dekker, F. W.,
Dorr, P. J. & Sprij, A.J. (2010). Timing of Group B Streptococcus screening in
pregnancy: A systematic review. Gynecologic and Obstetric Investigation, 69, 174-183.
