Include Group B Streptococcus Screening in Prenatal Care Visits
How to prevent a leading cause of neonatal morbidity and mortality
By Jacob Curtis, DO and Paula Mackrides, DO, FAAFP
Introduction
Group B streptococcus remains the single most common cause of neonatal sepsis and a major cause of neonatal disease and death in the United States. Although neonatal mortality has changed very little in the last 30 years, collectively speaking, Group B streptococcus (GBS) treatment has made a significant impact in reducing preventable neonatal deaths.1
Invasive Group B streptococcus disease emerged in the 1970’s as a leading cause of neonatal morbidity and mortality in the United States. In the 1980’s, clinical trials demonstrated that administering antimicrobials intrapartum to those with GBS colonization protected their newborns from early-onset disease.
In 1996, the CDC, in collaboration with ACOG, AAFP and AAP formally recommended intrapartum antimicrobial prophylaxis. In 2002, endorsed revised guidelines were issued that favored universal screening of pregnant women.2
The purpose of this article is to review the most recent literature concerning GBS as it applies to prenatal care, and to present practical applications in approaching questions we may be regularly asked in the outpatient setting.
Why the Osteopathic
Family Physician?
Osteopathic family physicians are in a unique position to play a primary role in the prevention of this disease. Among the tenets of osteopathic medicine is the commission to look beyond the disease. We can effectively do so as we focus upon the host.
According to a membership survey, nearly 20 percent of family physicians currently deliver babies. Another 15-20 percent provide at least some component of prenatal care. Also, 40 percent of family physicians report that they have provided obstetric care at some point in their practice.
Moreover, greater than 90 percent of family physicians regularly care for pediatric patients within their practice. This reminds each of us that we have a significant opportunity to educate our patients regarding prevention of this potentially deadly disease.3
Epidemiology
Group B streptococcus colonizes the gastrointestinal and genital tracts in humans. Approximately 30 percent of women are
GBS carriers.4
The carriage rate is the most critical determinant of risk for early-onset GBS infection in newborns. GBS colonization in and of itself is not harmful and is usually not treated, except at the time of delivery. However, there is suggestion that an asymptomatic GBS bacteriuria is associated with an increased risk of preterm birth (see treatment below for recommendations).
Non-GBS asymptomatic bacteriuria has previously been well established as a contributing cause of preterm birth and low birth weight infants.5
Among colonized women, there is a 50 percent probability of transmitting the bacteria to the newborn. Infants who are colonized have a 1-2 percent risk of developing infection. Infected babies can develop pneumonia, septicemia, or meningitis.
Prior to 1996, the incidence of newborn infections was 1-3/1000 within the first six days of life, of whom, 5-10 percent would die from the disease. For newborns seven days to three months, there was a .5-1.7/1000 incidence of developing infections. Following release of the 1996 guidelines, the incidence was reduced by 75 percent.
Diagnosis
In the 2002 guidelines, the CDC, in collaboration with ACOG, AAFP, and AAP recommended that all pregnant women should be screened for GBS colonization with swabs of both the lower vagina and the perirectal area at 35 to 37 weeks of gestation.6, 7
This recommendation was influenced by a large study from 1999 that demonstrated that routine screening and prophylaxis for carriers prevented more cases of early-onset disease than the obstetrical risk factor-based method that was used previously.8
The only patients who are excluded from screening are those with GBS bacteriuria (including asymptomatic disease) earlier in the current pregnancy or those who gave birth to a previous infant with invasive GBS disease. These latter patients are not included in the screening recommendation because they should receive intrapartum antibiotic prophylaxis (IAP) regardless of the colonization status.6
Screening for asymptomatic bacteriuria is standard practice at the first prenatal visit. However, it is important to note that presently the literature is unclear as to how often women should be screened. The literature is also unclear as to whether or not a simple urine dip is sufficient for screening purposes.9
Treatment
Oral antepartum treatment of colonized women is not effective because colonization cannot be eliminated with antenatal antibiotic administration.10 Antepartum antibiotics are only indicated for treatment of GBS-related infection, such as cystitis and asymptomatic bacteriuria.
Intravenous IAP are the mainstay of standard treatment. Penicillin G (5 million units IV initially, then 2.5 million units IV every 4 hours) is deemed universally sensitive because of its narrow spectrum of activity and remains the gold standard in treatment. Ampicillin (2g IV initially, then 1 g IV every 6 hours) is an acceptable alternative.
The risk for neonatal penicillin allergies is rare. When an allergic response does occur in a newborn, most often it presents as a self-limited rash. Newborn anaphylaxis to penicillin has been accepted as essentially non-existent.6
The greatest efficacy is achieved if the antibiotic used is administered ≥ 4 hours before delivery.11, 12 In a study of 4,535 women, the relationship between timing of ampicillin administration and rate of neonatal group B streptococcal transmission was as follows: less than 1 hour before delivery, 46 percent; 1-2 hours, 29 percent; 2-4 hours, 2.9 percent; and more than 4 hours, 1.2 percent.
Among the 253 mothers who received no intrapartum prophylaxis, colonization was found in 120 of their newborns (47 percent).13
Patients recommended for IAP
After screening has been performed, IAP is recommended for the following patients:
Among women with a history of non-immediate-type penicillin-allergy (i.e., at low risk for anaphylaxis), cefazolin (2 g initial dose, then 1 g every 8 hours) is recommended.
Antibiotic sensitivity testing of GBS cultures has been suggested in women with contraindications to receiving penicillin or cefazolin therapy. Clindamycin (900 mg IV every 8 hours) or erythromycin (500 mg IV every 6 hours) is recommended for patients at high risk for anaphylaxis to penicillin, only if their GBS culture screening isolate is documented to be susceptible to one of these agents.
It is important to note that the physician should notify the lab if the patient is penicillin allergic when the initial GBS culture is sent. Also, the physician must specifically ask the lab to check for clindamycin and erythromycin sensitivity, as this is not routine protocol. If high risk and resistant to Clindamycin and Erythromycin, Vancomycin (1gram every 12 hours) should be given.14
IAP is not recommended for the following patients:
Treatment Effectiveness
Since the introduction of the revised IAP guidelines in 2002, there has been a further reduction in the incidence of GBS disease to 0.34/1000 live births in 2003. This is consistent with the 2004 and 2005 data. This is a 75 percent decrease in the infection rate prior to the initial 1996 guidelines.15
Despite the success there is significant room for improvement. A 2003 study assessing GBS testing rates in eight different states discovered only 52 percent of 600,000 live births had been tested.16 Also, a 2002 survey of 306 obstetricians revealed that only 57 percent of providers appropriately cultured women for BS in both the vaginal and anorectal region.17
The Future of Intrapartum
GBS Prophylaxis?
Rapid Screen at Delivery
The findings of a retrospective review of live births at a large urban tertiary center suggest that traditional screening misses a small but significant subset of GBS positive mothers. This strongly suggests that methods of detection with greater sensitivity would be useful.18
One possible suggestion is to perform a rapid screen at the time of presentation in labor. Researchers from Stanford University performed a cost-benefit analysis using a new rapid PCR (45 minute results with 100 percent sensitivity and 98 percent specificity). Their results suggested that use of a rapid screen would result in fewer maternal courses of antibiotics, fewer perinatal infections, and a reduction in infant deaths.19 This has yet to be demonstrated in randomized controlled trials.
Antibiotic Resistance
An additional question raised is whether or not the extensive use of IAP could result in increased antibiotic resistance. A few cohort studies have explored this issue and have noted neither an increased rate of GBS infection, nor a change in the antibiotic resistance patterns after the recommendations were introduced.20-21
To the contrary, other studies have found an increase in the incidence of early onset neonatal sepsis with non-GBS organisms, and an increase in pathogens resistant to the antibiotic that was administered. Case control studies have also yielded conflicting results.22-24 The next several years will play a critical role in providing further information concerning this topic.
Vaccines
Several GBS multi-valent vaccine trials are currently underway to contribute to the reduction of GBS in the neonate. The theory is that women could be vaccinated prior to pregnancy to prevent vertical transmission at the time of delivery.
Improving Communication
It is important to note that diagnosis without clear communication hampers success in appropriate treatment. The author has found it helpful to write down on a prescription paper the patients GBS status, (including PCN allergy if appropriate), which she is then encouraged to keep in her purse.
This action has tremendously increased success in communication with the labor and delivery department when prenatal records are not readily available. Specifically, this small measure has been responsible in avoiding unnecessary antibiotics where GBS status would have other been unknown.
In conclusion, although GBS screening and treatment at delivery has now become the standard of care, those providing obstetrical care on
the maternity floor remain far from 100 percent adherent to these straightforward recommendations. As we take strides within our individual practices to further educate, test, and appropriately treat our patients, we will contribute significantly to the reduction of the morbidity and mortality associated with this preventable disease.
Jacob Curtis is a 2004 graduate of the Kirksville College of Osteopathic Medicine, Kirksville, Missouri. He received his certification at the KCOM/SIU Quincy Family Medicine Residency program in 2007. He is currently completing an obstetrics fellowship in South Bend, Indiana.
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