In the November 19, 2010 Morbidity and Mortality Weekly Report, the Centers for Disease Control and Prevention (CDC) published updated guidelines for screening, detecting, and treating Group B streptococcus (Group B strep) during pregnancy. Some of the changes to the guidelines, which were first recommended in 1996, address ways in which laboratories can improve detection and determine who requires prophylaxis.
Group B strep are bacteria commonly found in the urinary, digestive, and reproductive tracts of men and women. The bacteria colonize these areas in people, meaning they are present but usually do not cause symptoms. However, if Group B strep are present in the genital and rectal areas of pregnant women during labor and delivery, the bacteria can be passed to the newborns and possibly cause serious infections such as pneumonia, sepsis, or meningitis in the newborn.
Group B strep colonize about 10% to 30% of pregnant women. Since the majority of pregnant women are not colonized, it is not practical to treat all with an antibiotic. This could potentially lead to bacterial resistance to the antibiotic.
Screening is the most realistic means of determining who requires treatment, and current practices have helped to minimize the number of infections in newborns. The primary test is a culture of vaginal and rectal sites performed between 35 and 37 weeks of pregnancy. The test is done close to a woman's due date because the number of bacteria that are present can change over time. Screening is performed earlier if a woman goes into premature labor or if her "water breaks" early (premature rupture of membranes). Those who test positive for Group B strep are given an intravenous antibiotic during labor.
Though existing testing procedures have been successful in preventing many infections, Group B strep is still the number one infectious cause of disease and deaths in newborns in the US. To further reduce these infections, the CDC outlined new ways to test for the bacteria. New culture media have been developed to make it easier to identify the presence of Group B strep when the swabs are cultured in the laboratory. Molecular tests can be used to speed detection of the bacteria in women already in labor who have not been tested previously and have no known risk factors for transmitting the bacteria. Examples of risk factors include premature labor, fever and prolonged rupture of membranes. The molecular method, however, is not as sensitive as culture, so it should not be used to replace culture for routine screening of women at 35 to 37 weeks of pregnancy. Susceptibility testing is recommended on Group B strep cultured from women who are allergic to penicillin and have a high risk for anaphylaxis. The susceptibility results will determine which alternative antibiotic will be most effective for prophylaxis.
With additional options for testing, more GBS colonization may be detected and pregnant women may get treated appropriately, and the rate of newborn infections may be reduced further. Women who are pregnant should ask their doctor about Group B strep testing and know their status as their due date approaches.
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NOTE: This article is based on research that utilizes the sources cited here as well as the collective experience of the Lab Tests Online Editorial Review Board. This article is periodically reviewed by the Editorial Board and may be updated as a result of the review. Any new sources cited will be added to the list and distinguished from the original sources used.
Centers for Disease Control and Prevention. Prevention of Perinatal Group B Streptococcal Disease. Revised Guidelines from CDC 2010 Recommendations and Reports, November 19, 2010 / 59(RR10);1-32. Available online at http://www.cdc.gov/mmwr/preview/mmwrhtml/rr5910a1.htm?s_cid=rr5910a1_e through http://www.cdc.gov. Accessed January 2011.
Centers for Disease Control and Prevention. Group B Strep Information Page. Available online at http://www.cdc.gov/groupbstrep/index.html through http://www.cdc.gov. Accessed January 2011.
Mitchell, David. CDC Updates Guidelines on Prevention of Perinatal Group B Streptococcal Disease. American Academy of Family Physicians. 12/15/2010. Available online at http://www.aafp.org/online/en/home/publications/news/news-now/clinical-care-research/20101215gbsguidelines.html through http://www.aafp.org. Accessed January 2011.