Williams Manual of Pregnancy Complications, 23 ed.

CHAPTER 84. Group A and B Streptococcus Infections

Puerperal infection caused by group A Streptococcus (Streptococcus pyogenes) is rarely encountered today. These infections are particularly virulent and the organism produces a number of toxins and enzymes; M3 superantigen strains are particularly severe. Postoperative or postpartum infection outbreaks may be nosocomial from asymptomatic carriage in health-care workers. The organism produces a toxic shock-like syndrome that is often fatal. Prompt penicillin treatment, often combined with surgical debridement, may be lifesaving. Unlike group B streptococcal (GBS) infections where the neonate is most vulnerable, group A infections primarily affect the mother.

Asymptomatic carriage of group B Streptococcus (S agalactiae) is common, especially in the vagina and rectum (20 to 30 percent of women at 35 weeks’ gestation). Infection is associated with preterm labor, prematurely ruptured membranes, chorioamnionitis and puerperal sepsis, as well as with both fetal and neonatal infections.

Half of newborns born to women carrying group B streptococcus become colonized at birth. Intrapartum fetal transmission from the colonized mother may lead to severe neonatal sepsis soon after birth. The overall attack rate of sepsis is less than 1 per 1000 live births. Although preterm or low-birth-weight infants are at highest risk, more than half of the cases of neonatal sepsis are in term infants because the number of term births far exceeds those preterm.

Neonatal GBS sepsis: Infection in infants before 7 days is defined as early-onset disease. In some cases, the infant is born acidemic and depressed. In many neonates, septicemia includes signs of serious illness that usually develop within 6 to 12 hours of birth. These include respiratory distress, apnea, and shock. At the outset, therefore, the illness must be differentiated from idiopathic respiratory distress syndrome (see Chapter 90). The mortality rate with early-onset disease has declined to 4 percent. Unfortunately, it is not uncommon for surviving infants to develop neurological abnormalities sustained during hypotension from the sepsis syndrome.

Late-onset disease usually manifests as meningitis a week or more (7 days to 3 months) after birth. The mortality rate, although appreciable, is less for late-onset meningitis than for early-onset disease. Here again, neurological sequelae are common in survivors.

Prevention strategies: As of 2002, The American Congress of Obstetricians and Gynecologists and the Centers for Disease Control and Prevention advocate a culture-based screening approach to identify women who should receive intrapartum prophylaxis. These guidelines were updated in November 2010 (see Table 84-1). Women are screened for GBS colonization at 35 to 37 weeks, and intrapartum antimicrobials are given to rectovaginal carriers. Previous siblings with GBS invasive disease and prior identification of GBS bacteriuria in any trimester of the current pregnancy are also considered indications for prophylaxis. A risk-based approach is recommended for women with unknown GBS culture results at the time of labor. Preterm labor and preterm rupture of membranes are managed as detailed in Figures 84-1 and 84-2, respectively.

TABLE 84-1. Indications and Nonindications for Intrapartum Antibiotic Prophylaxis to Prevent Early-Onset Group B Streptococcal (GBS) Disease

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FIGURE 84-1 Algorithm for screening for group B streptococcal (GBS) colonization and use of intrapartum prophylaxis for women with preterm labor (PTL). aAt <37 weeks and 0 days’ gestation. bIf patient has undergone vaginal-rectal GBS culture within the preceding 5 weeks, the results of that culture should guide management. GBS-colonized women should receive intrapartum antibiotic prophylaxis. No antibiotics are indicated for GBS prophylaxis if a vaginal-rectal screen within 5 weeks was negative. cSee Figure 84-3 for recommended antibiotic regimens. dPatient should be regularly assessed for progression to true labor; if the patient is considered not to be in true labor, discontinue GBS prophylaxis. eIf GBS culture results become available prior to delivery and are negative, then discontinue GBS prophylaxis. fUnless subsequent GBS culture prior to delivery is positive. gA negative GBS screen is considered valid for 5 weeks. If a patient with a history of PTL is re-admitted with signs and symptoms of PTL and had a negative GBS screen >5 weeks prior, she should be rescreened and managed according to this algorithm at that time. (Adapted from Centers for Disease Control and Prevention: Prevention of perinatal group B streptococci disease. Revised guidelines from the CDC. MMWR 59(RR-10): 1–36, 2010.)

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FIGURE 84-2 Algorithm for screening for group B streptococcal (GBS) colonization and use of intrapartum prophylaxis for women with preterm premature rupture of membranes (pPROM). aAt <37 weeks and 0 days’ gestation. bIf patient has undergone vaginal-rectal GBS culture within the preceding 5 weeks, the results of that culture should guide management. GBS-colonized women should receive intrapartum antibiotic prophylaxis. No antibiotics are indicated for GBS prophylaxis if a vaginal-rectal screen within 5 weeks was negative. cAntibiotics given for latency in the setting of pPROM that include ampicillin 2 g intravenously (IV) once, followed by 1 g IV every 6 hours for at least 48 hours are adequate for GBS prophylaxis. If other regimens are used, GBS prophylaxis should be initiated in addition. dSee Figure 84-3 for recommended antibiotic regimens. eGBS prophylaxis should be discontinued at 48 hours for women with pPROM who are not in labor. If results from a GBS screen performed on admission become available during the 48-hour period and are negative, GBS prophylaxis should be discontinued at that time. fUnless subsequent GBS culture prior to delivery is positive. gA negative GBS screen is considered valid for 5 weeks. If a patient with pPROM is entering labor and had a negative GBS screen >5 weeks prior, she should be rescreened and managed according to this algorithm at that time. (Adapted from Centers for Disease Control and Prevention: Prevention of perinatal group B streptococci disease. Revised guidelines from the CDC. MMWR 59(RR-10): 1–36, 2010.

Because of concern about ampicillin-resistant organisms, especially Escherichia coli, penicillin G is recommended by many for intrapartum prophylaxis. Ampicillin is an acceptable alternative. For women with penicillin allergy, if the risk for anaphylaxis is low, cefazolin is recommended. If the risk is high, selection of a prophylactic agent is dependent on GBS susceptibility testing for clindamycin and erythromycin. Resistant strains require vancomycin.

In early 1995 at Parkland Hospital, we adopted the American College of Obstetricians and Gynecologists risk-based approach for intrapartum antimicrobial treatment for high-risk pregnancies. In addition, all neonates whose mothers were not given intrapartum antibiotic prophylaxis are treated in the delivery room with aqueous procaine penicillin G, 50,000 units intramuscularly. With this program, early-onset group B infection was decreased from 1.6 per 1000 to 0.4 per 1000 births.


For further reading in Williams Obstetrics, 23rd ed.,

see Chapter 58, “Infectious Diseases.”