An estimated 25% of pregnant women carry the group B streptococcus (GBS) bacteria. GBS is the leading cause of early onset-sepsis, which occurs in the first week of life and carries a high risk for infant mortality. Later-onset sepsis is also a significant risk in infants up to age 3 months, who present with fever, feeding difficulties, limpness, irritability or lethargy, breathing difficulties, or a blue color to the skin. Long-term complications of GBS in infants include the potential for deafness and developmental disabilities, and an estimated 4% to 6% of babies who contract GBS will die from the disease.
In 2002, the Centers for Disease Control and Prevention recommended prenatal screening for all women at 35 to 37 weeks of pregnancy, followed by intrapartum antibiotic prophylaxis (IAP) for those who are colonized with the bacteria, the combination of which was very successful in reducing the incidence of sepsis in infants in the United States. Despite this, GBS still causes more than one-third of cases of invasive early onset-sepsis, leading to a continued search for better solutions.
Screening for GBS bacteria involves taking vaginal and rectal swabs during routine office visits. The high percentage of unrecognized/untreated cases, however, indicates the need for methods to maximize collection efforts. New technologies, such as matrix-assisted laser desorption ionization-time of flight mass spectrometry, have provided a faster, more accurate methods of identifying GBS in samples compared with the standard of blood agar plates. In addition, the recent development of new chromogenic media to enhance identification have significantly improved the isolation of GBS in vaginal and rectal samples to 90% to 100%.
These methods are effective for patients who are screened and treated, and predelivery screening would catch many of the remaining cases, according to Stephanie Schrag, DPh, epidemiology team lead from the National Center for Immunization and Respiratory Diseases, a division of the Centers for Disease Control and Prevention. “Probably the biggest advance would be a simple bedside kit that allows for screening on presentation to labor. Such a kit ideally would enable labor and delivery staff to perform the test, have a turn-around time less than 30 minutes, and have sensitivity and specificity of at least 90%,” Dr Schrag said in an interview with Infectious Disease Advisor. “Ideally, such a test would also be able to detect mutations that confer resistance to clindamycin/erythromycin in order to guide antibiotic choice for women with penicillin allergy at high risk for anaphylaxis,” she reported.
Intrapartum Antibiotic (Antimicrobial) Prophylaxis
In current practice in the United States, IAP is offered to pregnant women who are identified as “colonized” with vaginal-rectal GBS bacteria after the 35th week of pregnancy, pregnant women who previously delivered an infant with invasive GBS disease, or pregnant women who have been diagnosed with GBS themselves during pregnancy.
Penicillin remains the first-line agent for treatment, Dr Schrag said, with ampicillin an acceptable alternative. Small adjustments to recommendations have been made in cases of penicillin allergy, where cefazolin is the preferred agent, except for women at high risk for anaphylaxis and where the options depend on susceptibility testing.
Antibiotic resistance presents some concerns, as IAP increases rates of Gram-negative infections, especially among very-low-birth-weight infants. “For any bacteria, we must always be vigilant for emergence of new antibiotic resistance profiles of concern,” Dr Schrag told Infectious Disease Advisor.
“To date, for GBS, penicillin and ampicillin resistance have not emerged. However, there are some single step mutations in the genes for penicillin binding proteins that have been detected, and we must continue to monitor these. Resistance to clindamycin and erythromycin does exist, and has been increasing over the last 15 years.”
Prenatal Vaccine for GBS
An attractive option in development for the future is a maternal GBS vaccine. A recent study by Kim et al8 reported that at an efficacy of 90% or greater, a pentavalent vaccine alone would prevent less GBS disease than the current combination of prepartum screening and IAP, but at a lower cost. Maternal immunization as an adjunctive strategy to IAP in unimmunized pregnant women would prevent more GBS than the current recommendations at a similar cost, and require only about 70% efficacy to the vaccine.
“Currently there is no licensed maternal vaccine,” Dr Schrag pointed out, “but several companies are engaged in development with high-income countries like the United States, as well as low- and middle-income countries, as the desired targets. The Bill and Melinda Gates Foundation is actively investing in this area, and public health agencies are providing technical assistance. Such a vaccine holds promise to prevent disease in the first week of life (the portion of disease preventable by intrapartum antibiotics) and, in addition, to prevent disease in infants 7 to 89 days of age (approximately 850 cases annually in this late-onset group in the United States each year).”
When asked what other strategies could improve GBS rates in the meantime, Dr Schrag suggested, “The best we can do now is to focus efforts on strong implementation of the perinatal GBS prevention recommendations. Potential further reductions in disease burden are possible through improved implementation, particularly for preterm deliveries and for women with penicillin allergy.” She pointed out that the Centers for Disease Control and Prevention has developed an app called Prevent Group B Strep to aid with the implementation of the guidelines. “Some healthcare systems are developing clinical decision support tools within their electronic medical records to further assist with guidelines implementation,” Dr Schrag said. Her team has been working on a program called the System to Prevent GBS Infections (SToP GBS), a tool embedded in electronic medical records designed to offer clinicians patient-specific recommendations to prevent the spread of GBS from mother to child during labor and delivery.
Source: Infectious Disease Advisor