Group B Strep in Pregnancy: What You Need to Know

What are the current recommendations for dealing with Group B Strep during pregnancy?

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Robert Steele

Robert W. Steele, MD, is a board certified pediatrician at St. John's Regional Health Center in Springfield, MO. He graduated from medical... Read more

What Is Group B Strep?
Group B Streptococcus (GBS) is the most common cause of sepsis (blood infection) and meningitis (infection of the fluid and lining surrounding the brain) in newborns.

Between 10 and 35 percent of women carry this bacteria within the vagina and or the lower intestine. Most of the time, the bacteria does not cause any symptoms in the pregnant woman, although it can cause bladder and uterine infections (amnionitis, endometritis).

It is a different story in the newborn infant. Usually, babies are exposed to Group B Strep during labor and delivery, becoming infected when they swallow or inhale the bacteria. There is also evidence that GBS may cross intact membranes to expose the baby while it is still in the womb.

Exposure to GBS can cause life-threatening infection of the blood (sepsis) or infection of the fluid and lining surrounding the brain (meningitis). The majority of infections in newborns occur within the first week of life and most infections become evident in the baby's first three months of life.

What Babies Are at Risk?

Any baby who is delivered from a mom who tests positive for the bacteria has some risk of getting this infection. A cesarean delivery does not prevent mother-to-child transmission of Group B Strep.

This disease remains a relatively uncommon one despite the large number of pregnant women who have this bacterium. (Before prevention methods were widely used, approximately 8,000 babies in the U.S. would get GBS disease each year. One of every 20 babies with GBS disease dies from infection.)

6 Risk Factors in Moms
1. Labor or rupture of membranes before 37 weeks pregnancy
2. Rupture of membranes 18 hours or more before giving birth
3. GBS carriage late in pregnancy
4. Fever in the mom during labor
5. Urinary tract infection due to GBS
6. Previous baby with GBS disease

Why Not Treat Every Pregnant Woman?
It seems like an obvious question. The vagina and rectum can be easily tested for the presence of this bacterium, and the bacterium can be eliminated -- or at least significantly reduced --with antibiotics. However, what to do about this potential threat to the infant has been a source of controversy for many years. This stems primarily from four facts:

1. Colonization of the vagina and rectum with Group B strep is transient. The fact that a woman tests negative one day does not mean she couldn't acquire the bacterium the next day. The opposite is true as well, the bacterium may go away on its own without antibiotics.

2. The test to confirm the presence of Group B strep takes at least 24 hours.

3. The widespread use of antibiotics causes bacteria to become resistant.

4. Giving antibiotics to the mother during labor and delivery substantially reduces the risk of serious infection in the infant. Antibiotics easily pass through the placenta. Thus, giving the antibiotics to the mother is about the equivalent of giving the infant antibiotics directly.

Testing women for Group B strep has not reduced the risk of infection to the infant, because those mothers who are negative may become positive before delivery, and those who are positive and treated with antibiotics may become positive again before delivery. You can't test women when they arrive to the hospital in labor because the test takes 24 hours, and, to be effective, the antibiotics need to be administered during labor.

We could give all pregnant women in labor antibiotics, but that is not without short-term risk (allergic reactions, inducing other infections, etc.) and long-term risk (rapidly inducing resistance to antibiotics).

Current Recommendations
-- All women between 35 to 37 weeks of pregnancy should be routinely screened for GBS colonization by collecting a swab from the vagina and rectum.
-- All women identified as GBS carriers, by culture, should be offered intravenous antibiotics at the time of labor or rupture of the membranes -- even if no other risk factors are present. Colonization during a previous pregnancy is not an indication for antibiotics in subsequent births.

If a woman has not had a GBS cultures prior to the onset of labor or rupture of the membranes, prophylactic intravenous antibiotics should be administered if any of the following are present:
-- Pregnancy of less than 37 weeks
-- The membranes have been ruptured 18 hours or longer
-- A temperature of 100.4 degrees F (38 degrees C) or greater.

Women with the following conditions should receive intravenous antibiotics during labor, whether or not they tested postived for GBS:
-- Previous baby with GBS disease
-- Urinary tract infection due to GBS

The following updated recommendations for the prevention of Group B Strep disease are based on critical appraisal of multistate population-based observational data and several studies from individual institutions that have been completed since publication of previous CDC, ACOG and AAP (8) recommendations. They replace previous recommendations from CDC.

Obstetric-care practitioners, in conjunction with supporting laboratories and labor and delivery facilities, should adopt the following strategy for the prevention of perinatal GBS disease based on prenatal screening for GBS colonization. The risk-based approach is no longer an acceptable alternative except for circumstances in which screening results are not available before delivery.

All pregnant women should be screened at 35 to 37 weeks' gestation for vaginal and rectal GBS colonization. At the time of labor or rupture of membranes, intrapartum chemoprophylaxis should be given to all pregnant women identified as GBS carriers. Colonization during a previous pregnancy is not an indication for intrapartum prophylaxis in subsequent deliveries. Screening to detect GBS colonization in each pregnancy will determine the need for prophylaxis in that pregnancy.

Women with GBS isolated from the urine in any concentration (e.g., 103) during their current pregnancy should receive intrapartum chemoprophylaxis because such women usually are heavily colonized with GBS and are at increased risk of delivering an infant with early-onset GBS disease. Labels on urine specimens from prenatal patients should clearly state the patient's pregnancy status to assist laboratory processing and reporting of results. Prenatal culture-based screening at 35 to 37 weeks' gestation is not necessary for women with GBS bacteriuria. Women with symptomatic or asymptomatic GBS urinary tract infection detected during pregnancy should be treated according to current standards of care for urinary tract infection during pregnancy.

Women who have previously given birth to an infant with invasive GBS disease should receive intrapartum chemoprophylaxis; prenatal culture-based screening is not necessary for these women.

If the result of GBS culture is not known at the onset of labor, intrapartum chemoprophylaxis should be administered to women with any of the following risk factors: gestation less than 37 weeks, duration of membrane rupture less than 18 hours or a temperature of greater than 100.4? F (greater than 38.0?C). Women with known negative results from vaginal and rectal GBS screening cultures within 5 weeks of delivery do not require prophylaxis to prevent GBS disease even if any of the intrapartum risk factors develop.

Women with threatened preterm (less than 37 weeks' gestation) delivery should be assessed for need for intrapartum prophylaxis to prevent perinatal GBS disease. An algorithm for management of women with threatened preterm delivery is provided. Other management approaches, developed by individual physicians or institutions, may be appropriate.

Culture techniques that maximize the likelihood of GBS recovery are required for prenatal screening. Collection of specimens for culture may be conducted in the outpatient clinic setting by either the patient, with appropriate instruction, or health-care provider. This involves swabbing the lower vagina and rectum (i.e., through the anal sphincter). Because lower vaginal as opposed to cervical cultures are recommended, cultures should not be collected by speculum examination. Specimens should be placed in a nonnutritive transport medium (e.g., Amies or Stuart's without charcoal). Specimen labels should clearly identify that specimens are for group B streptococcal culture. If susceptibility testing is ordered for penicillin-allergic women, specimen labels should also identify the patient as penicillin allergic and should specify that if GBS is isolated, it should be tested for susceptibility to clindamycin and erythromycin. Specimens should be inoculated into a selective broth medium (examples of appropriate commercially available media include Trans-Vag Broth supplemented with 5 percent defibrinated sheep blood or LIM broth), incubated overnight, and subcultured onto solid blood agar medium. Methods of testing prenatal isolates from penicillin-allergic women for susceptibility to clindamycin and erythromycin are outlined. Laboratories should report culture results (positive and negative) and susceptibility testing results to the anticipated site of delivery (when known) and to the health-care provider who ordered the test.

Health-care providers should inform women of their GBS screening test result and the recommended interventions. In the absence of GBS urinary tract infection, antimicrobial agents should not be used before the intrapartum period to treat GBS colonization. Such treatment is not effective in eliminating carriage or preventing neonatal disease and may cause adverse consequences (DI).

GBS-colonized women who have a planned cesarean delivery performed before rupture of membranes and onset of labor are at low risk for having an infant with early-onset GBS disease. These women should not routinely receive intrapartum chemoprophylaxis for perinatal GBS disease prevention.

For intrapartum chemoprophylaxis, the following regimen is recommended for women without penicillin allergy: penicillin G, 5 million units intravenously initial dose, then 2.5 million units intravenously every 4 hours until delivery. Because of its narrow spectrum of activity, penicillin is the preferred agent. An alternative regimen is ampicillin, 2 g intravenously initial dose, then 1 g intravenously every 4 hours until delivery.

Intrapartum chemoprophylaxis for penicillin-allergic women takes into account increasing resistance to clindamycin and erythromycin among GBS isolates. During prenatal care, history of penicillin allergy should be assessed to determine whether a patient is at high risk for anaphylaxis, i.e., has a history of immediate hyper-sensitivity reactions to penicillin (e.g., anaphylaxis, angioedema, or urticaria) or history of asthma or other conditions that would make anaphylaxis more dangerous. Women who are not at high risk for anaphylaxis should be given cefazolin, 2 g intravenously initial dose, then 1 g intravenously every 8 hours until delivery. For women at high risk for anaphylaxis, clindamycin and erythromycin susceptibility testing, if available, should be performed on isolates obtained during GBS prenatal carriage screening. Women with clindamycin- and erythromycin-susceptible isolates should be given either clindamycin, 900 mg intravenously every 8 hours until delivery; OR erythromycin, 500 mg intravenously every 6 hours until delivery. If susceptibility testing is not possible, susceptibility results are not known, or isolates are resistant to erythromycin or clindamycin, the following regimen can be used for women with immediate penicillin hypersensitivity: vancomycin, 1 g intravenously every 12 hours until delivery.

Routine use of antimicrobial prophylaxis for newborns whose mothers received intrapartum chemoprophylaxis for GBS infection is not recommended. However, therapeutic use of these agents is appropriate for infants with clinically suspected sepsis. An updated algorithm for management of infants born to mothers who received intrapartum chemoprophylaxis for GBS infection is provided. This revised algorithm is not an exclusive approach to management; variation that incorporates individual circumstances or institutional preferences may be appropriate.

Local and state public health agencies, in conjunction with appropriate groups of hospitals, are encouraged to establish surveillance for early-onset GBS disease and to take other steps to promote perinatal GBS disease prevention and education to reduce the incidence of early-onset GBS disease in their states. Efforts to monitor the emergence of perinatal infections caused by other organisms are also encouraged.

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