Chemoprophylaxis

Recommendations for prevention of early-onset neonatal GBS infection are based on data comparing a maternal culture screening method to a risk-based method to identify women who should receive intrapartum antimicrobial prophylaxis that demonstrated significantly better efficacy for culture screening than with a risk-based method. Recommendations from the Centers for Disease Control and Prevention (CDC)¹ include the following:

• All pregnant women should be screened at 35 to 37 weeks' gestation for vaginal and rectal GBS colonization (see Fig 3.4). The only exceptions to this recommendation for universal culture screening are women with GBS bacteriuria during the current pregnancy or women who have had a previous infant with invasive GBS disease; these women always should receive intrapartum chemoprophylaxis. At the onset of labor or rupture of membranes, intrapartum chemoprophylaxis should be given to all pregnant women identified as carriers of group B streptococci. Colonization during a previous pregnancy is not an indication for intrapartum chemoprophylaxis unless screening results are positive in the current pregnancy.
  
  
  
  
  


• Women with group B streptococci isolated from urine in any concentration during their current pregnancy should receive intrapartum chemoprophylaxis, because these women usually are heavily colonized with group B streptococci and are at increased risk of delivering an infant with early-onset GBS disease; culture screening at 35 to 37 weeks' gestation is not necessary.


• Women who previously have given birth to an infant with invasive GBS disease should receive intrapartum chemoprophylaxis; culture screening is not necessary.


• If GBS status is not known at onset of labor or rupture of membranes, intrapartum chemoprophylaxis should be administered to women with any of the following risk factors: gestation less than 37 weeks, duration of membrane rupture 18 hours or longer, or intrapartum temperature of 38.0°C (100.4°F) or greater.


• Culture techniques that maximize the likelihood of recovery of group B streptococci are required for prenatal screening. The optimal method for GBS screening cultures is collection of 1 or 2 swabs of the lower vagina and rectum; placement of swabs in a nonnutrient transport medium; removal of swabs and inoculation into selective broth medium, such as Trans-Vag Broth supplemented with 5% defibrinated sheep blood or Lim broth; overnight incubation; and subculture onto solid blood agar medium.


• Oral antimicrobial agents should not be used to treat women who are found to have GBS colonization during culture screening unless there is a GBS urinary tract infection warranting Treatment according to obstetric standards of care. Such Treatment is not effective in eliminating carriage of group B streptococci or preventing neonatal disease.


• Women who have GBS colonization and have a planned cesarean delivery performed before rupture of membranes and onset of labor should not receive intrapartum chemoprophylaxis routinely.


• For intrapartum chemoprophylaxis, intravenous penicillin G (5 million U initially, then 2.5 million U every 4 hours until delivery) is the preferred agent because of its efficacy and narrow spectrum of antimicrobial activity. An alternative regimen is intravenous ampicillin (2 g initially, then 1 g every 4 hours until delivery).


• Because of increasing prevalence of GBS resistance to both erythromycin and clindamycin (20%-40%), cefazolin (2 g initially, then 1 g every 8 hours) is recommended for women who are allergic to penicillin but at low risk of anaphylaxis. Cefazolin is recommended because of its narrow spectrum of activity and ability to achieve high amniotic fluid concentrations. Women whose GBS isolates are tested and found to be clindamycin susceptible and who are at high risk of anaphylaxis with penicillin can receive this drug at a dose of 900 mg every 8 hours. Vancomycin should be reserved for penicillin-allergic women who are at high risk of anaphylaxis (ie, type I hypersensitivity) and for whom GBS isolate susceptibility testing has not been performed; vancomycin should be administered intravenously, 1 g every 12 hours until delivery. The efficacy of clindamycin or vancomycin is not established.


• Routine use of antimicrobial agents as chemoprophylaxis for neonates born to mothers who have received adequate intrapartum chemoprophylaxis for GBS disease is not recommended. However, therapeutic use of these agents is appropriate for infants with clinically suspected systemic infection.

An approach for empiric management of newborn infants born to women who receive intrapartum chemoprophylaxis to prevent early-onset GBS disease or to treat suspected chorioamnionitis is provided in Fig 3.5. These guidelines are based on published information as well as expert opinion and are as follows:

• If a woman receives intrapartum antimicrobial agents for Treatment of suspected chorioamnionitis, her newborn infant should have a full diagnostic evaluation and empiric antimicrobial therapy pending culture results, regardless of clinical condition at birth, duration of maternal therapy before delivery, or weeks of gestation at delivery. Empiric therapy for the infant should include antimicrobial agents active against group B streptococci as well as other organisms that might cause early-onset neonatal sepsis (eg, ampicillin and gentamicin).


• If clinical signs in the infant suggest sepsis, a full diagnostic evaluation should include a lumbar puncture, if feasible. Blood cultures can be sterile in as many as 15% to 38% of newborn infants with GBS meningitis, and the clinical management of an infant with abnormal CSF differs from that of an infant with normal CSF. If a lumbar puncture has been deferred for a neonate receiving empiric antimicrobial therapy and therapy is continued beyond 48 hours because of ongoing clinical findings suggesting infection, CSF should be obtained for measurement of white blood cell count and differential, glucose, and protein and for culture.


• Initiation of intrapartum antimicrobial prophylaxis for the woman with nontype I allergy to penicillin with cefazolin if administered at least 4 hours before delivery can be considered adequate. The effectiveness of other agents (eg, clindamycin or vancomycin) in preventing early-onset GBS disease has not been studied, and no data are available to suggest the duration before delivery of these regimens that can be considered adequate.


• On the basis of the demonstrated effectiveness of intrapartum antimicrobial prophylaxis in preventing early-onset GBS disease and data indicating that clinical onset occurs within the first 24 hours of life in more than 90% of infants, hospital discharge at 24 hours after birth may be reasonable under certain circumstances. Specifically, a healthy-appearing infant who is at least 38 weeks' gestation at delivery and whose mother received 4 or more hours of intrapartum penicillin, ampicillin, or cefazolin before delivery may be discharged home as early as 24 hours after delivery if other discharge criteria have been met and a person able to comply fully with instructions for home observation will be present. A key component of following instructions is the ability of the person observing the infant to communicate with health care professionals by telephone and to transport the infant promptly to an appropriate health care facility if clinical signs of systemic infection develop. If these conditions are not met, the infant should remain in the hospital for at least 48 hours of observation.

Neonatal Infection Control

Routine cultures to determine whether infants are colonized with group B streptococci are not recommended. Epidemiologic evaluation of late-onset or late, late-onset cases in a special care nursery may be required to exclude a health care-associated source.

Nursery Outbreak

Cohorting of ill and colonized infants and use of contact precautions during an outbreak are recommended. Other methods of control (eg, Treatment of asymptomatic carriers with penicillin) are ineffective. Routine hand hygiene by health care professionals caring for infants colonized or infected with GBS is the best way to prevent spread to other infants.