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January 19, 2009

Group B Strep: The Preventable Infection
By Kim M. Norton
For The Record
Vol. 21 No. 2 P. 24

The most common infection in newborns can be prevented with prenatal screening.

Group B streptococcus (GBS) bacteria lives in adults’ gastrointestinal tracts, bladders, bowels, vaginas, and throats. It is a naturally occurring bacterium that comes and goes—“carriers” often never know whether they have GBS nor do they necessarily display symptoms associated with the bacteria.

However, for women who are pregnant and test positive for GBS, the bacteria pose serious risks, including death, for their newborns if antibiotics are not given intravenously at birth.

In 2002, the Centers for Disease Control and Prevention (CDC) updated its guidelines from an earlier 1996 risk-based strategy. The current recommendation calls for universal prenatal screening for vaginal and rectal GBS colonization of all pregnant women between 35 and 37 weeks gestation. According to the CDC, risk factors associated with GBS colonization at the onset of labor are a fever of 100.4˚F or higher, the bag of waters has been broken for more than 18 hours, and preterm labor at less than 37 weeks.

“Culturing is by far better than waiting for risk factors to appear, because in some cases, they never do,” says Elizabeth A. Deckers, MD, an obstetrician and gynecologist with Aurora Healthcare in Wisconsin.

In 2001, according to the CDC, approximately 1,600 newborns in the United States developed early onset disease, defined as the presentation of a GBS infection in a newborn less than 1 week old. “A GBS infection in a newborn can be devastating because it affects multiple systems,” says Charles F. Potter, MD, SC, a neonatologist with Aurora Healthcare in Milwaukee. Symptoms of a GBS infection in a newborn generally develop within the first 24 hours, and 99% of cases show up by 48 hours, he says.

“Giving antibiotics to the pregnant woman reduces exposure to the bacteria but does not eliminate the risk,” Potter says. “[Physicians should] observe the baby for 24 to 48 hours and avoid early discharge. In cases where the baby shows any abnormality, treatment should be started immediately just in case of exposure.”

GBS colonization not only poses serious complications for the newborn but also for the mother. Pregnancy-related infections due to GBS range from sepsis and amnionitis (infection of the uterus) to urinary tract infections and possible stillbirth, according to the CDC.

What Is GBS?
GBS is not a sexually transmitted disease. Rather, it is a naturally occurring bacterium in the body that can appear periodically. Because of this characteristic, it is not uncommon for a woman who was GBS positive during her first pregnancy to be GBS negative in subsequent pregnancies. However, precautions must be taken if the mother is GBS positive to safeguard against possible infection in the newborn.

Intrapartum chemoprophylaxis (antibiotics) are administered intravenously during delivery to protect the baby from possible infection. The CDC indicates that a woman with GBS has a one in 200 chance of delivering a baby with the bacteria if no antibiotics are administered. However, that drops to one in 4,000 when they are given.

Should a child contract GBS from the mother, the antibiotics will kill the bacteria in the short term. “However, GBS is a serious infection in a newborn that can cause serious life-long effects such as asthma, arthritis, and possible development of a neurological disease,” says Brenna Anderson, MD, a maternal-fetal specialist at Women & Infants Hospital in Providence, R.I.

There are two forms of GBS infection in newborns: early onset and late onset. Infants who develop a GBS infection when they are less than 1 week old have early onset and those older than 1 week have late onset. A late-onset GBS infection is not limited to infants; the bacteria can affect the elderly and adults with other illnesses, such as diabetes or liver disease, according to the CDC. Of the two forms of the disease, early onset is the most devastating and deadly for newborns.

C-Section vs. Vaginal Delivery
Generally, the type of birth (Caesarean section vs. vaginal delivery) does not affect how a doctor will proceed with regards to GBS. What is most important is whether the baby is exposed to the bacteria and how best to protect him or her from possible infection. “If the bag of water remains intact, the baby is not exposed to the bacteria. And if it is broken, the baby is exposed,” says Anderson. The antibiotics will wipe out the bacteria in the vagina, plus they will transfer to the baby to help him or her fight a possible infection, she adds.

According to CDC guidelines, a C-section should not be used to prevent early-onset GBS infection in infants. Also, if the C-section is planned and the mother is identified as having GBS, antibiotics need not be given unless labor has begun or the water breaks prior to the surgery.

No matter what birthing option a GBS-infected mother chooses, it’s essential that she be aware of her condition. “If [the mother knows] she is GBS colonized and her water breaks, it is important she gets to the hospital immediately to protect the baby from infection,” says Anderson. It is recommended that antibiotics be administered at least four hours prior to birth to be most effective against infection, she adds.

Warning Signs
“The risk factors for a GBS colonization are not yet known, but 20% to 30% of women will have it when pregnant,” says Deckers. “If the results of the screening culture are not available, then treatment will depend on risk factors present during labor.”

Should a newborn be exposed to GBS, there are signs parents can monitor to determine whether their child may be infected, including difficulty breathing or respiratory disease, poor color, tachycardia, hypoglycemia, shock, poor feeding, seizures, and apnea.

“If the symptoms of the infection are left untreated, GBS can cause sepsis, meningitis, neurological disability, and possibly even death,” says Potter. In the majority of cases, the infection is categorized as being early onset. Rarely, late-onset disease occurs, with the most common symptom being meningitis. Other signs may include inconsolable screaming, fever, lack of appetite, or grunting, or the baby may be stiff, limp, or floppy.

“In infants younger than one week, GBS infection can result in sepsis, pneumonia, and meningitis, with mortality rates reported between 4.7 percent and 9 percent. GBS infection that becomes clinically apparent after one week of age is most likely to present as meningitis and occurs in 0.2 per 1,000 live births, with a mortality rate of 2 percent to 2.8 percent,” according to American Family Physician.

To determine whether a baby has been infected with GBS, a blood or spinal fluid sample is tested for infection. If infected, the newborn is generally treated with intravenous antibiotics, says Potter. However, by following the CDC’s guidelines for proper prenatal screening, the condition can be prevented, says Potter.

— Kim M. Norton is a New Jersey-based freelance writer specializing in healthcare-related topics for various trade and consumer publications.

Incidence of Group B Strep Has Decreased Among Newborns But Increased Among Adults
Group B streptococcus (GBS), a major cause of serious infections, declined about 25% among infants younger than 7 days old from 1999 to 2005 but increased nearly 50% among those aged 15 to 64, according to a study published last spring in The Journal of the American Medical Association.

In the 1970s, GBS emerged as the leading cause of sepsis and meningitis during the first week of life. Subsequent prevention strategies resulted in substantial declines in disease in infants younger than 7 days old. Guidelines for preventing this disease near the time of birth were revised in 2002. Disease trends following the release of these guidelines have not yet been well studied.

In addition to illness during the first week of life, GBS also causes invasive disease in older infants, pregnant women, children and young adults with underlying medical conditions, and older adults. “The epidemiology of group B streptococcal disease is dynamic, and continued surveillance to monitor trends across age groups is necessary. For example, an increase in disease incidence among nonpregnant adults has been documented in past decades, but whether that trend has continued is unknown,” the authors wrote. In the United States in 2005, GBS caused an estimated 21,500 cases of invasive disease and 1,700 deaths, according to the article.

Christina R. Phares, PhD, of the Centers for Disease Control and Prevention, and colleagues evaluated trends and characteristics over a recent period among cases of laboratory-confirmed invasive GBS disease identified by population-based surveillance in 10 states participating in the Active Bacterial Core Surveillance of the Emerging Infections Program Network.

From 1999 through 2005, surveillance identified 14,573 cases of invasive GBS disease, of which 1,232 were early-onset disease. Disease incidence decreased 27% after the 2002 release of revised early-onset disease prevention guidelines, from 0.47 per 1,000 live births from 1999 to 2001 to 0.34 per 1,000 live births from 2003 to 2005. Incidence remained stable among infants aged 7 to 89 days and pregnant women.

GBS incidence increased 48% for those aged 15 to 64, while those aged 65 and older experienced a 20% increase. Among persons aged 15 to 64, incidence increased from 3.4 per 100,000 population in 1999 to 5 per 100,000 in 2005; among those aged 65 and older, incidence increased from 21.5 per 100,000 to 26 per 100,000. These values translate to a 32% increase in the overall incidence of adult disease, which reached 7.9 per 100,000 in 2005. The proportion with known outcome who dies was highest in the oldest age groups.

All 4,882 isolates tested were susceptible to the antibiotics penicillin, ampicillin, and vancomycin, but 32% and 15% were resistant to erythromycin and clindamycin, respectively.

“Maternal group B streptococcus vaccination trials should be a public health priority, followed by expanded vaccine development to target disease among elderly and younger adults with chronic underlying conditions,” the authors concluded.