In 2002, the Centers for Disease Control and Prevention (CDC) updated the guidelines for screening pregnant women in the United States for the risk of Streptococcus agalactiae, or group B Streptococcus (GBS) colonization.1 The former guidelines from 1996 established screening based on a pregnant mother's risk of developing GBS colonization. Risk was associated with age, race, amount of prenatal care, previous colonization with GBS, and preterm delivery. Women at risk for GBS were given intrapartum antimicrobial prophylaxis (IAP), or antimicrobial therapy during pregnancy. The 1996 guidelines lowered the rate of GBS colonization from 1.7 cases per 1,000 live births in 1993 to 0.6 cases per 1,000 live births in 1998.2 The updated guidelines issued in 2002 recommended universal screening for GBS of all pregnant women. This strategy decreased the amount of GBS colonization by 27%.2
The guidelines were revised again in 2010. 1 In this article we will highlight the guidelines of the 2010 document and examine the effect the guidelines are expected to have on the GBS colonization of pregnant women and the incidence of neonatal GBS infections.
Significance of GBS
In the United States, GBS is one of the most common causes of morbidity and mortality in infants. Currently, GBS infection occurs in 0.3 - 0.4 cases out of 1,000 live births.1 Neonatal group B streptococcal disease presents in two clinical syndromes: early-onset, which affects the infant at less than a week old or late-onset, which affects the infant greater than a week old. The disease is transmitted vertically from a GBS colonized mother to her infant either during pregnancy or around birth. GBS vaginal or rectal colonization occurs in 10% to 30% of pregnant women3, leading to neonatal sepsis, pneumonia, meningitis, chorioamnionitis, myonecrosis of the uterus, neonatal pneumonia, premature delivery, bacteremia, and other serious complications during pregnancy.4
An infant's risk of early-onset disease is greatest with maternal colonization during pregnancy; other risk factors include black race, young age, previous GBS colonization during pregnancy, long membrane rupture, or a gestational age of less than 37 weeks.1 Identifying GBS early in the pregnancy and administering IAP in the form of antibiotics, such as penicillin or Cefazolin, reduces the incidence of GBS.2 The CDC's updated 2010 guidelines are meant to decrease the incidence of GBS in pregnant women by identifying and treating GBS infection with IAP early in the pregnancy.1
The 2002 guidelines were based on the data at the time about effective GBS treatments. These guidelines reduced the number of GBS infections by 27% since the release of the 1996 guidelines.2 New data and evidence available since the 2002 update concerning the prevention of GBS disease led the CDC to revise the guidelines. The 2010 revised guidelines were developed by a working group established by the CDC that included representatives from several professional medical societies. Updates to the guidelines include extended information regarding the laboratory diagnosis of GBS, including colony-count; updates to the recommended penicillin-G dosage for affected mothers; revisions to the prophylaxis protocols for women with penicillin allergies; and updates to the recommended care for newborns at risk for early-onset disease.1 The CDC guidelines are based on the idea that universal screening and IAP are the keys to preventing early-onset GBS in newborns.
GBS Specimen Processing
The procedures for GBS specimen collection and processing are presented with the revised 2010 guidelines. GBS specimen collection consists of swabbing the lower vagina and then rectum using a single swab or two different swabs at 35-37 weeks gestation. The swab is placed in a nonnutritive transport medium, such as Stuart's or Amies medium and kept at room temperature or in a refrigerator if available. Samples can be kept and bacteria remain viable at room temperature; however, GBS recovery declines after 1-4 days after the initial collection if the sample is not refrigerated.
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