Obgyno Wino Podcast Episode 23 - Prevention of Group B Streptococcal Early-Onset Disease in Newborns
Updated: Aug 16, 2019
"In training a child to activity of thought, we must beware of what I will call 'inert ideas'--that is to say, ideas that are merely received into the mind without being utilised, or tested, or thrown into fresh combinations...Every intellectual revolution which has ever stirred humanity into greatness has been a passionate protest against inert ideas. Then, alas, with pathetic ignorance of human psychology, it has proceeded by some educational scheme to bind humanity afresh with inert ideas of its own fashioning." - Alfred North Whitehead, "Aims of Education"
CO#782 - Published July 2019
Group B streptococcus (GBS) is the leading cause of newborn infection, with the primary risk factor being maternal colonization of the genitourinary and gastrointestinal tracts
10-30% of women are colonized by GBS; colonized women have a 50% chance of passing the bacteria to their newborn during a vaginal delivery; of colonized newborns, 1-2% will develop early-onset GBS disease (EOGBSD)
Antibiotic prophylaxis intrapartum can reduce risk of EOGBSD from 1-2% to 0.25% (though no great studies have been published)
EOGBSD is nasty and carries 2-3% mortality among term infants and up to 30% for infants born at < 33 wga
Pregnant women should be universally screened for GBS colonization prior to the onset of labor. In the absence of a positive screen, patients who are preterm, who have prolonged ROM, who have a history of GBS colonization in a prior pregnancy, or who had a prior infant affected by GBS sepsis
What is GBS (aka Strep agalactiae)?
- colonizes the GU or GI tract of 10-30% of women
- if GBS ascends to the uterus from the vagina, it could infect the newborn and cause serious infection
- prenatal care providers will recommend culturing the vagina/perineum/anus at 36-37w6d weeks to detect colonization; if present, antibiotic prophylaxis will be recommended in labor to prevent vertical transmission to the newborn
- cultures are viable for 5 weeks
- it can also be detected in the urine; in any quantity in the urine, there's a greater chance of colonization at 36-37w6d, which is why a culture isn't indicated in the presence of a positive urine culture resulted at any point in pregnancy (P.s. Don't treat the bacteriuria unless 100,000 CFUs or more. Treatment doesn't eliminate colonization.)
Note: This is a subtle change from the CDC's guidelines in 2010, which recommended screening between 35-36w6d. The reason for the change was to extend the life of the culture to 41 wga
What is the risk that the newborn gets sick?
- two types of infection: early-onset (within 7 days of birth) and late-onset
- 50%: the risk that a newborn born to a mother colonized with GBS will become colonized themselves
- 1-2%: percentage of colonized newborns who will develop EOGBSD
- the risk of EOGBSD is reduced to 0.25% - 0.5% if mom is treated with intrapartum antibiotic prophylaxis
- this is all fine and dandy, but Cochrane reviewed this topic and concluded that "Intrapartum antibiotic prophylaxis appeared to reduce EOGBSD, but this result may well be a result of bias as we found a high risk of bias for one or more key domains in the study methodology and execution. There is lack of evidence from well designed and conducted trials to recommend IAP to reduce neonatal EOGBSD."
- incidence of EOGBSD has dropped, though, from 1.8 newborns per 1000 live births in the 90s to 0.23 per 1000 live births in 2015, presumably secondary to antibiotic prophylaxis
- EOGBSD can be scary: sepsis, pneumonia, meningitis (rare); usually manifests within the first 12-48 hrs after birth
- EOGBSD carries higher morbidity and mortality w/ preterm infants
- reports from the CDC are old, but they suggest a mortality rate of 2-3% among term infants diagnosed with EOGBSD and as high as 30% for preterm infants < 33 wga
- survivors of neonatal GBS meningitis will also likely have long-term morbidity
- also of note, there's an increased risk of PTD in women colonized by GBS (risk even higher in GBS bacteriuria compared to those with GBS detected on rectovaginal culture)
Will the antibiotics affect my newborn's gut microbiome?
Who should receive antibiotic prophylaxis in labor?
- women with a urine culture that grows GBS (any number of CFUs qualifies!)
- women with a positive rectovaginal culture during universal screening between 36-37w6d
- If GBS status is unknown, prophylaxis is recommended if:
preterm labor (<37 wga)
prolonged ROM (>18 hours) or intrapartum fever
history of neonatal GBS sepsis
- reasonable to offer prophylaxis if GBS status unknown and patient was colonized in a prior pregnancy (50% chance of colonization)
- prophylaxis is not recommended for pre-labor c-section
A quick note on the rectovaginal culture
- in order to guide antibiotic selection (below), specimens requisitions should indicate pregnancy status, known pencillin allergies
- the specimen will be testing for clindamycin susceptibility as well as a D-zone test, which indicates the presence of inducible resistance to erythromycin
- nucleic acid amplification testing (NAAT) may be more sensitive, but it doesn't provide the opportunity to test for susceptibilities
Note: Penicillin is better than ampicillin because it has a narrower, more targeted spectrum of antimicrobial activity against gram-positive bacteria and lower likelihood of inducing resistance in other vaginal organisms
More on PCN allergies and cross-tolerance with cephalosporins
- most people who claim to be allergic to PCN are actually tolerant
- sensitivity is lost over time
- severe reactions are immediate type 1 IgE-mediated immune reactions that develop within the first few hours of administration
- it was previously reported that 8-10% of individuals with PCN-induced anaphylaxis would have a similar reaction to cephalosporins
- more recent data suggests that it's closer to 4% (1st or 2nd gen cephalosporins) or even <1% (3rd or 4th gen cephalosporins)
- if you have any doubt, you can recommend PCN allergen testing
- if type 1 reaction ruled out in this testing, you will improve their ability to treat PCN-sensitive infections for the rest of their life
- Clindamycin is an alternative for patients with true anaphylaxis, but resistance is rising and susceptibility testing should be completed; if it's not completed, vancomycin is the recommended alternative (20 mg/kg IV q8hr w/ maximum of 2 g per single dose)
Duration of antibiotic prophylaxis in labor
- the more doses, the less likely the neonate will require neonatal diagnostic evaluations for sepsis and the lower the risk of empiric antibiotic administration to the neonate
- 1.6% risk if less than 2 hrs of antibiotics prior to delivery
- 0.9% risk if between 2 and 4 hrs
- 0.4% risk if at least 4 hrs of antibiotics
What do you do in PPROM?
- if PPROM occurs between 34w0d and 36w6d, induce labor and provide GBS prophylaxis (unless GBS bacteriuria was detected prior)
- if PPROM occurs at <34 wga, collect a GBS rectovaginal culture and begin latency antibiotics
- the standard latency antibiotic regimen is 48 hrs of ampicillin + 1 dose of azithromycin followed by 5 days of amoxicillin OR 48 hrs of IV ampicillin + erythromycin follows by 5 days of oral amoxicillin + erythromycin) --> these regimens cover GBS
- in the event of PCN allergy, 1st-gen cephalosporin (e.g. cephalexin) or clindamycin/azithromycin alone for patients w/ anaphylactic reaction
Is membrane sweeping OK if my patient is colonized with GBS?
Are frequent vaginal exams associated with greater risk of EOGBSD?