Group B streptococcal (GBS) is one of the leading infectious causes of death and disease in newborns. GBS bacteria are common in adults – nearly one in four women in the United States is a carrier, which merely means that the bacteria may come and go within her body without actively causing infection. Most women will carry GBS at some point in their lifetime. While carrying the bacteria in the vagina and/or rectum is usually not problematic for women, the bacteria can be transmitted either shortly before or during childbirth, causing severe disease in infants. The majority of these infections in newborns occur within the first week of life, and are known as “early-onset” GBS disease. Infected newborns may become seriously ill with sepsis (blood infection) or pneumonia, or less often, the bacteria may cause meningitis – which can lead to hearing loss and deafness in surviving children. “Late-onset” GBS disease occurs in infants one week to several months after birth. Unfortunately, about three babies out of every 10,000 may appear healthy at birth and develop symptoms of late-onset GBS after the first week of life. Meningitis, a common cause of deafness and hearing loss, is more often a result of late-onset GBS disease than early-onset GBS disease.
An Historical Perspective
While the number of women who are asymptomatic carriers of GBS seems remarkably high, nearly 98 percent of the infants born to mothers who carry GBS at the time of labor will be without symptoms. Sadly, without intervention, one to two percent of infants will develop early-onset disease. During the 1970s, around half of the infants who developed early-onset GBS died of their illness. During that time, it is estimated that 7,500 cases of GBS disease in infants occurred each year.
Epidemiologic studies – broad-based studies that look at disease patterns across populations – were conducted in the 1980s, demonstrating that women who were carriers of GBS during pregnancy were 25 times more likely than women who were not carriers to deliver infants with early-onset GBS disease. Learning to recognize the symptoms early and improved treatment of newborns helped bring down the fatality rate from 50 percent to 15 percent but more significant prevention efforts were still needed. Clinical trials in the 1980s showed that giving at-risk women antibiotics through the vein during labor was highly effective at preventing early-onset GBS infections in their newborns.
In the 1990s, collaboration among medical groups, researchers, professional organizations and public advocacy groups brought about clinical guidelines to help prevent early-onset disease. At that point, two methods of identifying candidates for receiving antibiotics during labor were available for doctors to choose from – a “risk-based approach” or a “culture-based” screening method. The risk-based approach helped identify women who might be candidates for antibiotics during labor based upon some factors known to be associated with early-onset disease, including delivery before term, fever during labor or rupture of membranes (the amniotic sac surrounding the fetus) more than eighteen hours before the actual delivery. The “culture-based” approach relied on screening pregnant women to look for the GBS bacteria late in pregnancy and administering antibiotics during labor to carrier women. While the screening method would, in theory, prevent more cases, it wasn’t known at the time if it was truly more effective because of the real-life challenges of getting screening results to the delivery ward on time.
A New Generation of Prevention
Fast-forward to 2001. A new millennium provided new opportunities for prevention. Both clinical and public health experts had data collected from the 1990s and it warranted a fresh review of prevention strategies. Thanks to the 1996 guidelines, rates of newborn infection saw a large decline; however, in the U.S. in 2001, there were still about 1,700 babies less than one week old who suffered from the serious and sometimes deadly early-onset GBS disease.
In 2002, after a meeting of clinical and public health experts, the Centers for Disease Control and Prevention (CDC) issued new guidelines for the prevention of perinatal GBS disease. While there were several aspects of earlier recommendations which were updated (especially addressing premature labor, penicillin allergies and management of newborn infants), the highlight was a new recommendation for universal screening: culturing all pregnant women for GBS late in pregnancy.
The new guidelines were endorsed by the American Academy of Pediatrics and are consistent with guidelines released in 2002 by the American College of Obstetricians and Gynecologists, among other groups, helping to ensure that this strong message about screening every pregnant woman gets to the physicians in a position to do just that. In addition, a clear and united message about screening helps pregnant women partner with their doctors and be proactive in seeking preventive care. Because a woman may see one provider for prenatal care then a different clinician during the actual delivery, it is important for women to know their own status – and whether to expect antibiotics during labor.
The screening test is not invasive – it is a quick swab of the vagina and rectum during the 35th to 37th weeks of pregnancy – and it is covered by most insurance policies. While no screening test can prevent every case of GBS disease, a universal screening policy helps take the guesswork out of what should be routine care for all expectant mothers.
Unfortunately, trends in late-onset disease have remained stable, suggesting that antibiotics during labor are not effective at preventing infections with onset after the first week of life, when the risk of meningitis and consequent hearing loss is greater. Nelson’s Textbook of Pediatrics (17th edition) reports that studies from the 1970s and 1980s demonstrated that up to 30 percent of infants surviving GBS meningitis had major long-term neurological problems, including hearing loss. While the new screening policy should help further reduce the number of early-onset GBS cases, research on a GBS vaccine is still greatly needed to help prevent late-onset cases and the severe consequences of this terrible infection. With enhanced screening practices and new research, there is hope that future generations might never even need to ask the question “What is group B strep?”
The complete CDC recommendations as well as free resources for patients, clinicians and laboratorians are available at the CDC’s GBS Web site: www.cdc.gov/ groupbstrep.
