All women need to know how to help protect their babies from Group B Strep (GBS) evenif they have tested negative.
It’s important to know that:
1) A woman may test negative if her GBS colonization level at the time of the test was below the level of detection.
2) A woman’s GBS status can change so a woman could test negative but be colonized later in pregnancy. (Read more about prenatal-onset GBS disease prevention HERE.)
3) Culture tests can show a false negative. Possible reasons include:
Recent use of antibiotics or vaginal medications
Not swabbing both the vagina and rectum
Improper handling of the culture specimen
4) Test results are only considered to accurately (95%-98%) predict a woman’s colonization status at delivery if she delivers within 5 weeks of her test. A woman may need to be retested.
5) Once born, a baby can become infected with GBS by sources other than the mother. (Read more about early-onset GBS disease prevention HERE and late-onset GBS disease prevention HERE.)
Here’s what the US Centers for Disease Control and Prevention (CDC) says in the November 19, 2010 MMWR, Volume 59, No. RR-10, page 12 (unofficial translation from English),
“The multistate population-based study conducted during 2003–2004 also identified a greater-than-expected number of cases of early-onset GBS occurring among infants born to women with negative prenatal screening results (61% observed compared with 23%–46% expected cases of early-onset GBS disease among full-term infants) (102).
Some false-negative results are expected because culture is not perfectly sensitive and GBS can be acquired by the mother during the period between screening and delivery. However, the high proportion of cases born to women with negative screening results suggest possible problems in the steps required to identify GBS colonization. Suboptimal specimen collection timing, methods, transport, and/or laboratory processing might be contributing factors.
Among screened women, the date of the antenatal screening test was missing from 36% of labor and delivery charts. Documentation of the date allows for an assessment of whether screening was performed during the recommended gestation time window.”
(Page 10) “Although maternal GBS colonization might increase clinical suspicion for early-onset GBS disease in an infant, in the era of universal screening, >60% of early-onset GBS cases have occurred among infants born to women who had a negative prenatal GBS culture screen (102,203,204). False-negative cases are not unexpected because culture at 35–37 weeks’ gestation will fail to detect some women with intrapartum GBS colonization. As effective prevention strategies are increasingly implemented, a growing proportion of the remaining relatively low burden of disease will reflect inherent limitations in the strategies. Signs of sepsis in any newborn can be an indication of early-onset GBS disease, regardless of maternal colonization status.”
(Page 7) “Because GBS colonization status can change over the course of a pregnancy, the timing of specimen collection for determination of colonization status is important. Because colonization can be transient, colonization early in pregnancy is not predictive of early-onset GBS disease (44). Late third trimester colonization status has been used as a proxy for intrapartum colonization (140). The negative predictive value of GBS cultures performed ≤5 weeks before delivery is 95%–98%; however, the clinical utility decreases when a prenatal culture is performed more than 5 weeks before delivery because the negative predictive value declines (37).”
So it is important to be aware that GBS can infect babies before birth,during birth, and even by sources other than the mother up to several months of ageeven if the mother has tested negative. Stories of babies whose moms tested negative can be read HERE.
Please read “How to Help Protect Your Baby from Group B Strep (GBS) HERE” and our tear sheet “Even though you’ve tested negative for Group B Strep (GBS), learn how to help protect your baby” HERE. Both are available as downloads or to be shipped for use in perinatal offices or your community. Click HERE for ordering information.
Women who test negative are not usually treated with IV antibiotics during labor and delivery due to concerns about antibiotic resistance and altered vaginal flora.
(Simon, don’t need to translate references) 37. Yancey MK, Schuchat A, Brown LK, Ventura VL, Markenson GR. The accuracy of late antenatal screening cultures in predicting genital group B streptococcal colonization at delivery. Obstet Gynecol 1996;88):811–5.
44. Regan JA, Klebanoff MA, Nugent RP, et al. Colonization with group B streptococci in pregnancy and adverse outcome. VIP Study Group. Am J Obstet Gynecol 1996;174:1354–60.
102. Van Dyke MK, Phares CR, Lynfield R, et al. Evaluation of universal antenatal screening for group B Streptococcus. N Engl J Med 2009;360:2626–36. 140. Boyer KM, Gadzala CA, Kelly PD, Burd LI, Gotoff SP. Selective intrapartum chemoprophylaxis of neonatal group B streptococcal early-onset disease. II. Predictive value of prenatal cultures. J Infect Dis 1983;148:802–9.
203. Pulver LS, Hopfenbeck MM, Young PC, Stoddard GJ, Korgenski K, Daly J, et al. Continued early onset group B streptococcal infections in the era of intrapartum prophylaxis. J Perinatol 2009;29:20–5. 204. Puopolo KM, Madoff LC, Eichenwald EC. Early-onset group B streptococcal disease in the era of maternal screening. Pediatrics 2005;115:1240–6.