Group B Streptococcus (GBS) Infections

Group B streptococcus (GBS), also known as Streptococcus agalactiae, was once considered a pathogen of domestic animals only, causing mastitis in cows. S agalactiae is now best known as a cause of postpartum infection and as the most common cause of neonatal sepsis. More recently, numerous series have described S agalactiae as a cause of infection in nonpregnant adults, providing descriptions of the clinical spectrum of disease, including clinical features, risk factors, therapy, and outcomes of GBS infection in nonpregnant adults.

Group B streptococci colonize the vaginal and gastrointestinal tracts in healthy women, with carriage rates ranging from 15% to 45%. Neonates can acquire the organism vertically in utero or from the maternal genital tract during delivery. Although the transmission rate from mothers colonized with S agalactiae to neonates delivered vaginally is approximately 50%, invasive GBS disease develops in only 1% to 2% of colonized neonates.[1]

GBS neonatal sepsis is rare, but it is more common in the setting of prematurity and prolonged rupture of the membranes. Rates of mortality and morbidity are increased in preterm newborns with early-onset GBS disease.[2]  Because of the ubiquity of S agalactiae colonization in women and the rarity of GBS neonatal sepsis, prevention of the disease is difficult. Many pregnant women require treatment to prevent a single neonatal infection. Immunoprophylaxis and chemoprophylaxis have both been studied as solutions to this problem.

Neonatal GBS disease is divided into early and late disease. Early GBS neonatal sepsis often presents within 24 hours of delivery but can become apparent up to 7 days afterward. No specific clinical features differentiate early GBS disease from infections caused by other pathogens. Pneumonia with bacteremia is common, whereas meningitis is less likely.

Late GBS neonatal sepsis is defined as infection that presents between 1 week post partum and the age of 3 months. Late disease commonly involves GBS serotype III, typically characterized by bacteremia and meningitis.

The absence of antibody to GBS in infants is a risk factor for infection. Because antibodies to GBS provide protection against disease in animal models, there is an ongoing interest in vaccination as an approach to reducing the incidence of GBS colonization in healthy women. Vaccine development was once promising; however, shifting serotypes of GBS responsible for clinical disease have limited this approach. Other factors that have made this approach less attractive include problems related to access to vaccination by women of childbearing age and the emotional responses and possible litigation associated with vaccination during pregnancy.

The current approach to the prevention of GBS infection during pregnancy requires intrapartum antimicrobial prophylaxis in women at term who have culture evidence of recent vaginal or rectal GBS infection. This has become the standard owing to the efforts of the American College of Obstetrics and Gynecology and the Centers for Disease Control and Prevention in 2010 and 2020.[3, 4]  Women without a known GBS status delivering before 37 weeks' gestation with premature rupture of the membranes or intrapartum fever are also candidates for intrapartum antimicrobial prophylaxis. Administration of penicillin or ampicillin is the initial approach. Clindamycin and erythromycin used to be the standard in individuals with penicillin allergy, but group B streptococci are no longer always sensitive to these 2 drugs. Because of increasing resistance to clindamycin and erythromycin,[5]  vancomycin is now the agent of choice for pregnant women with high-risk penicillin allergy. Clindamycin should only be used if testing for resistance to clindamycin has been performed on GBS isolated cultures.[3]

Only in the last 3 decades has the role of group B streptococci as a serious pathogen in nonpregnant adults been well defined. Numerous studies have allowed description of the clinical spectrum of disease, including clinical features, risk factors, therapy, and outcomes.

Streptococcus agalactiae infection is becoming more common in nonpregnant adults and is almost always associated with underlying abnormalities. In published series, diabetes mellitus, obesity, and malignancy have been consistently reported as the most common underlying diseases associated with infection.[6] Other conditions associated with GBS infection in adults include HIV, cirrhosis, advanced kidney disease, cardiovascular and genitourinary abnormalities, neurologic deficits, steroid therapy, and peripheral vascular disease.[7]  Relapse is not uncommon, with approximately 5% of nonpregnant adults eventually experiencing a second episode of GBS disease.[8]

GBS infection in elderly people (≥70 years) is strongly linked to congestive heart failure and being bedridden; urinary tract infection, pneumonia, and soft-tissue infection are the most common manifestations of infection.[9]  Neurologic disease is associated with pneumonia in elderly people, possibly resulting from aspiration of group B streptococci from the upper respiratory tract. Nosocomial GBS infection is common in this group and is described in other series. The source of this infection is not always clear, but the genitourinary tract and skin are thought to be the sources of some nosocomial infections.

Group B streptococci are commonly found in the gastrointestinal tract and have been found to colonize the urethra in both men and women without causing infection. Group B streptococci can also colonize the upper respiratory tract. Colonization is also observed in wound and soft tissue cultures in the absence of obvious infection. Determining the site of origin of acquisition and transmission of S agalactiae can be puzzling because these bacteria are very invasive but produce little inflammation at the point of entry.

Primary GBS bacteremia without an obvious source is a common presentation in adults. Although one study suggests that GBS bacteremia is a low-grade infection and easily controlled with little morbidity, results of other studies suggest that the clinical presentation may be the same as that of classic sepsis with shock and may carry a high mortality rate. Sustained bacteremia may indicate endocarditis or an infected catheter. Group B streptococci can cause acute destructive endocarditis, which may require emergency valve replacement.

Urinary tract infections are a common manifestation of GBS disease and are observed in both pregnant and nonpregnant adults. Other presentations of GBS infection include pneumonia, skin and soft-tissue infections, septic arthritis, osteomyelitis, meningitis, peritonitis, and endo-ophthalmitis.

Group B streptococci remain sensitive to penicillin and ampicillin and were once also sensitive to cefazolin, erythromycin, and clindamycin. Although penicillin is the treatment of choice, it is unclear whether use of penicillin provides a better outcome than use of other antibiotics.

Streptococcus agalactiae is a gram-positive coccus that, when cultured on sheep blood agar, forms glistening gray-white colonies with a narrow zone of β hemolysis. It is an invasive encapsulated organism capable of producing severe disease in immunocompromised hosts. GBS infection in the absence of associated comorbid medical conditions is rare.

The virulence of S agalactiae is related to the polysaccharide toxin it produces. Immunity is mediated by antibodies to the capsular polysaccharide and is serotype specific. Several serotypes are known—Ia, Ib, Ic, II, III, IV, V, VI, VII, and VIII. In the United States, serotypes Ia, Ib, II, III, and V have been shown to be associated with invasive disease.[9]

Group B streptococci colonize the vagina, gastrointestinal tract, and the upper respiratory tract in healthy humans. The portal of entry is not apparent, but possible areas include the skin, genital tract, urinary tract, and respiratory tract.

Frequency

United States

GBS neonatal sepsis occurs in 1.8 to 3.2 per 1000 live births. In 2005, early GBS neonatal sepsis was observed in 0.35 per 1000 births, whereas late sepsis was observed in 0.33 per 1000 births.[10] The incidence has decreased from 1.8 per 1000 births in the 1990s to 0.23 in 2015, likely because of the implementation of the American College of Obstetricians and Gynecologists and Centers for Disease Control and Prevention guidelines for antibiotic prophylaxis for pregnant women with colonization with group B streptococci.[11]

Although the incidence of GBS disease in neonates appears to be decreasing, the rate in nonpregnant adults appears to be increasing, with an overall increase of 32% between 1999 and 2005 and an incidence of 8 cases per 100,000 population.[10]  In studies, investigators have estimated that in 2016, the rate for nonpregnant adults in the general public was approximately 11 cases per 100,000 population.[12]

International

The role of group B streptococci in the developing world is not well defined. However, a meta-analysis of GBS disease in 53 countries, published in 2017, showed a pooled incidence of invasive GBS disease of 0.49 per 1000 live births.[13]  The meta-analysis also showed the incidence of early-onset GBS disease to be 0.41 per 1000 births and the incidence of late-onset GBS disease to be 0.26 per 1000 births.[13]  Carriage rates and serotypes in women in underdeveloped countries are similar to those observed in the industrial world.

Mortality and Morbidity

GBS disease results in significant mortality in both neonates and adults. Although the mortality rate ranges from 947% in published reports, most studies have revealed it to be approximately 20%.[8] The case fatality rate in the United States between 2008 and 2016 was found to be, on average, 6.5% for invasive GBS infection.[12]  The mortality rate is highest in elderly patients with comorbid medical conditions, and the manifestations most likely to result in death include endocarditis, meningitis, and pneumonia. The high mortality rate in elderly people with GBS infection may not reflect the organism itself but the predisposing condition or conditions that put the individual at risk for GBS infection.

The mortality rate for neonatal GBS infection is much lower than that for GBS infection in nonpregnant adults. An increasing awareness of GBS infection in infants has led to improved outcomes in recent years.

Postpartum GBS infection is associated with a low mortality rate because the group at risk is composed of healthy young or middle-aged women.

Race

GBS infection is more common in Black individuals than in White individuals and is much more common in older Black adults than in older White adults. These differences are probably due to socioeconomic factors rather than race.[12]

Sex

Young and middle-aged women who undergo obstetric and gynecologic manipulation have an increased risk for GBS infection.

Among nonpregnant patients, GBS infection has no sexual predilection. Incidence has been increasing in men compared with women in the United States.[12]

Age

The mean age of adult patients with GBS infection is 64 years.

A bimodal distribution is well recognized. Young and middle-aged healthy women with GBS infection secondary to obstetric or gynecologic manipulation is one group, and the second group is elderly persons with GBS infection as a complication of preexisting illness.

History

GBS infection in healthy adults is becoming more prevalent in nonpregnant adults and is almost always associated with underlying comorbidities, with diabetes and obesity being the most common in some series.[12] This association, which the authors have observed over the last 25 years, is unexplained. Malignancy was the most common association in a study from an institution with a large population of patients with cancer.

Cardiovascular and genitourinary abnormalities have also been identified as major factors that predispose individuals to GBS infection. Other conditions associated with GBS infection in adults include neurologic deficits, cirrhosis, steroids, AIDS, renal dysfunction, and peripheral vascular disease. In elderly people aged 70 years or older, GBS infection is strongly linked with congestive heart failure and being bedridden.

GBS pneumonia is rare and has few unique features. It is observed in elderly people with diabetes or with neurologic deficits and may result from aspiration of group B streptococci that colonize the upper airway. In one study, GBS pneumonia appeared to be associated with a high rate of bacteremia.

GBS meningitis, a common manifestation of neonatal infection, is uncommon in adults. It is almost always associated with anatomic abnormalities contiguous with, or of, the central nervous system, usually as a result of neurosurgery.

Multiple studies have shown that GBS bacteremia is one of the most common clinical manifestations of invasive GBS disease.[9] Although a genitourinary, soft-tissue, or line-related source of infection is possible, no source of infection can be identified in most cases. Bacteremia with an unknown source accounts for approximately 25% of all cases of invasive GBS disease in some studies.[8] GBS pneumonia in elderly people has been associated with bacteremia. Endocarditis should always be strongly considered in patients with bacteremia without an identified source. Often, the diagnosis becomes obvious because GBS endocarditis is very destructive and frequently necessitates valve replacement for valve insufficiency.

Other manifestations of GBS infection include skin and soft-tissue infection, osteomyelitis, arthritis, diskitis, and colonization of foot infections and decubitus ulcers in patients with diabetes. Although medical therapy should resolve many GBS infections, those involving skin, soft tissue, and bone may not be resolved with antibiotics alone and may require surgical intervention. GBS infections leading to necrotizing fasciitis and toxic shock syndrome have been documented.[8, 14]

Chorioamnionitis, endometritis, and the full spectrum of urinary tract infections (from asymptomatic bacteriuria to cystitis and pyelonephritis with bacteremia) are observed with GBS infection. These are common complications often related to childbirth in young and middle-aged women. Urinary tract infections with group B streptococci are also observed in elderly men and women, often those with diabetes or genitourinary abnormalities.

Pneumonia may occur in bedridden elderly patients with neurologic deficits and fever, shortness of breath, chest pain, pleuritic pain, or cough.

Meningitis may be seen in the neurosurgical patient with fever, headache, nuchal rigidity, or confusion.

Bacteremia, line-related infection, sepsis, or endocarditis may develop in patients with fever, malaise, confusion, chest pain, shortness of breath, myalgia, or arthralgia

Skin and soft-tissue infection, osteomyelitis, or septic arthritis may occur in patients with diabetes or in elderly patients with fever, malaise, localized pain, cellulitis, arthralgia, arthritis, or weakness.

Urinary tract infection or pelvic abscess may develop in the postpartum woman or older man or woman with fever, dysuria, flank pain, or pelvic pain.

Physical examination may reveal the following conditions:

• Pneumonia in bedridden elderly patients with neurologic deficit and fever, lung consolidation, pleural effusion, tachypnea, tachycardia, or hypotension
• Meningitis in the neurosurgical patient with fever, confusion, hypotension, headache, nuchal rigidity, or changing mental status
• Bacteremia, line-related sepsis, or endocarditis in the patient with fever, murmur, evidence of an embolic event, hypotension, phlebitis, tachycardia, tachypnea, splenomegaly, or evidence of heart failure
• Skin and soft tissue infection, osteomyelitis, septic arthritis, or discitis in elderly patients or those with diabetes who have fever, cellulitis, arthritis, arthralgia, localized pain, decubitus ulcer, vascular insufficiency of the lower extremity, back pain, wound infection, or neurologic dysfunction
• Urinary tract infection or pelvic abscess in the postpartum woman or older man or woman with fever, flank pain, pelvic pain, or abdominal pain

For pregnant women, both vaginal and rectal swabs should be obtained at 36 0/7 and 37 6/7 weeks of gestation.[3, 4]  A single swab is used for culture; first a specimen is obtained from the lower vagina, then a specimen is obtained from the rectum. This method increases the culture yield significantly when compared with either sampling from the cervix or rectum alone or a single vaginal swab without a rectal swab.[15] Samples can be collected by the patients themselves, and studies have shown that self-collected samples are as accurate as those collected by physicians.[16]

Gram staining of an appropriate specimen is a useful first test because it can reveal early streptococcal infection.

Isolation of group B streptococci from blood, cerebrospinal fluid, and/or a site of local suppuration is the only method for diagnosing invasive GBS infection.

GBS antigen may be detected in blood, cerebrospinal fluid, and/or urine and may aid in diagnosis in certain circumstances.

Consider pneumonia in the elderly bedridden patient with fever and other relevant symptoms and neurologic deficits. Radiographs may show infiltrate or effusion in such patients.

Consider meningitis in a patient who has undergone a neurosurgical procedure and has  fever and other relevant symptoms. CT scanning of the head may reveal an abscess or contiguous infection. Rule out increased intracranial pressure so lumbar puncture can be performed safely.

Consider bacteremia, endocarditis, and line-related sepsis in a patient with a fever. Echocardiography may reveal vegetations or evidence of valve destruction.

In a patient who is elderly, bedridden, or has diabetes with fever and relevant symptoms, consider soft-tissue infection, osteomyelitis, diskitis, epidural abscess, wound infection, necrotizing fasciitis, and decubitus ulcer. Radiography of the involved area may reveal evidence of gas or bone destruction. CT scans or MRI of the involved area may reveal phlegmon, abscess, or osteomyelitis.

In a postpartum woman or older man or woman with fever and relevant symptoms, consider urinary tract infection and pelvic abscess. Ultrasonography of the genitourinary tract or pelvis may reveal evidence of genitourinary obstruction or abscess. CT scans and MRI may show evidence of obstruction or abscess.

Although rapid tests are available for assessment of maternal GBS colonization at the onset of labor, a study of 2 rapid tests by Daniels et al revealed that neither was sufficiently accurate to recommend their routine use in clinical practice. Of the 2 tests, polymerase chain reaction proved significantly more accurate than optical immunoassay; nevertheless, when combined vaginal and rectal swabs were obtained, polymerase chain reaction had a sensitivity of 84% and a specificity of 87%. The authors concluded that screening using a rapid test was not cost effective based on its current sensitivity, specificity, and cost, and that intravenous antibiotic prophylaxis directed by screening with enriched culture at 35 to 37 weeks' gestation (timing base on old American College of Obstetricians and Gynecologists guidelines) is likely to be the most acceptable cost-effective strategy.[17]

Another study revealed that although intrapartum antibiotic prophylaxis was effective in preventing mother-to-newborn transmission of group B streptococci, prenatal cultures obtained by health care providers during routine care did not accurately predict the occurrence of infection found during labor.[18]

Schwope et al advise that, when collecting samples for GBS screening during a pelvic examination, practitioners should obtain the sample before using a bacteriostatic surgical lubricant. In a prospective cohort study of 168 patients, 20 patients had positive GBS test result before the pelvic examination, but only 10 of those had a positive GBS test result after a pelvic examination was performed with a chlorhexidine-based surgical lubricant.[19]

A patient with GBS pneumonia may require diagnostic and therapeutic thoracentesis if a pleural effusion is present; empyema requires drainage by thoracentesis, chest tube, or surgery.

A patient with GBS bacteremia, endocarditis, or line-related sepsis may require valve replacement because of destructive endocarditis.

A patient with a GBS soft-tissue infection, arthritis, osteomyelitis, diskitis, or epidural abscess may require diagnostic aspiration and curative surgery. Necrotizing fasciitis and septic arthritis are surgical emergencies. A patient with an epidural abscess may require emergency surgery.

A patient with a GBS urinary tract infection or pelvic abscess may require aspiration with ultrasonography or CT scan guidance for a diagnostic tap to isolate the organism, relieve obstruction, or drain an abscess.

Group B streptococci are likely to be sensitive to penicillin and ampicillin. However, resistance to penicillin has been increasing, as documented in studies done in Hong Kong and Japan.[20, 21] Group B streptococci have never been as exquisitely sensitive to penicillin as group A β-hemolytic streptococci; therefore, the initial therapy for GBS infection has always been high-dose parenteral penicillin or ampicillin. Cephalosporins, such as cefazolin and ceftriaxone, can often be used for the treatment of penicillin-sensitive infections.

Although clindamycin and erythromycin were at one time uniformly active against group B streptococci, resistance has been increasing. One large study that examined the susceptibility patterns of more than 4800 GBS isolates showed that 32% were resistant to erythromycin and 15% were resistant to clindamycin and that 99% of clindamycin-resistant strains were also resistant to erythromycin.[10] According to Centers for Disease Control and Prevention reports published between 2006 and 2009, GBS resistance to clindamycin ranged from 13% to 20%, and resistance to erythromycin ranged from 25% to 32%.[4]

In another study conducted in an upstate New York community hospital, investigators reported 38.4% resistance to clindamycin and 50.7% resistance to erythromycin in 688 GBS-positive cultures.[5]  Therefore, sensitivity testing should be done before these agents are used. Oral clindamycin remains an excellent agent for use after a course of parenteral therapy for bone, soft-tissue, and lung infections, if the isolate is susceptible.

Because of possible resistance to clindamycin, vancomycin remains the initial treatment of choice for GBS infection in patients who are allergic to penicillin. Penicillin, ampicillin, and vancomycin remain the treatments of choice for endocarditis. Although vancomycin may be adequate for treatment of GBS meningitis in patients who are allergic to penicillin, skin testing and desensitization for penicillin therapy might be considered. Penicillin has not been demonstrated to be superior to vancomycin for treatment of GBS endocarditis. There have been rare case reports of vancomycin-resistant strains of GBS.[22]

Although fluoroquinolones appear to have efficacy against isolates of group B streptococci, resistance to fluoroquinolones has recently been reported.[23]

In general, if ampicillin, penicillin, vancomycin, or ceftriaxone cannot be used, consultation with an infectious diseases specialist is strongly recommended. In situations in which an empiric antibiotic must be chosen, referring to the local antibiogram can be extremely helpful.

Consultation with a surgeon and surgical intervention are important.

Patients with pneumonia may require empyema drainage.

Patients with endocarditis, bacteremia, and sepsis may require heart valve replacement.

Patients with soft-tissue infection, septic arthritis, osteomyelitis, diskitis, and epidural abscess caused by GBS infection often require surgery combined with parenteral antibiotic therapy for resolution.

Necrotizing fasciitis and septic arthritis are surgical emergencies.

A patient with an epidural abscess may require emergency surgery.

Urinary tract infections and pelvic abscesses may require relief of genitourinary obstruction and abscess drainage for resolution.

Various consultations may be required for optimal outcomes in patients with GBS infection. An infectious diseases specialist can often be helpful in choosing the antibiotic and duration of therapy, especially if the susceptibility report shows resistance to penicillins, vancomycin, and cephalosporins.

Appropriate surgical support is critical for a good outcome.

Patients with pneumonia may require a pulmonologist or surgeon for empyema drainage.

Patients with bacteremia, endocarditis, or line-related sepsis may require a cardiovascular surgeon for valve replacement.

Patients with soft-tissue infections, osteomyelitis, epidural abscess, diskitis, or arthritis require a rheumatologist for arthrocentesis and an orthopedic surgeon or neurosurgeon for possible surgical opinion and intervention.

Patients with a urinary tract infection or pelvic abscess may require a urologist or gynecologist for surgical opinion and possible relief of obstruction and abscess drainage.

 The American College of Obstetricians and Gynecologists has updated guidelines on the prevention of early-onset GBS infection in newborns, which have replaced the third set of GBS prevention guidelines from the Centers for Disease Control and Prevention published in 2010.[3, 4]

In summary, the recommendations are to perform a universal GBS screening between weeks 36 0/7 and 37 6/7 of gestation, regardless of the planned mode of delivery. This provides a 5-week window for valid cultures, which increases the accuracy of predicting GBS colonization status at the time of delivery.[24, 25, 26]  Screening is best done with vaginal-rectal cultures. For patients with positive cultures, it is best to offer early intrapartum intravenous antibiotics because 2 hours of antibiotic administration has been shown to be effective in decreasing the frequency of neonatal sepsis by decreasing the GBS vaginal colonies.[27]

For prevention of early-onset GBS infection, penicillin G remains the agent of choice. For women with penicillin allergy in whom the risk for anaphylaxis is considered to be low and/or in whom the severity of a reaction is uncertain, first-generation cephalosporins can be used. For women with penicillin allergy in whom the risk for anaphylaxis is high, penicillin allergy testing should be performed, if available, and cultures should include testing for susceptibility to clindamycin. Intravenous vancomycin remains the agent of choice for patients with high-risk penicillin allergy and also for those with GBS isolates not susceptible to clindamycin.

The following scenarios are indications for intrapartum prophylaxis:

• Maternal history of delivery of a neonate with invasive GBS disease
• Positive GBS cultures obtained at 36 0/7 weeks of gestation or later during pregnancy
• GBS bacteriuria during any trimester of current pregnancy
• Unknown GBS status at onset of labor and any of the following:

            -Delivery before 37 0/7 weeks of gestation

            -Amniotic rupture of membranes 18 hours or more before delivery

            -Maternal fever (≥38 °C) during labor

            -Positive result of nucleic amplification testing for GBS

            -Negative result of nucleic amplification testing   for GBS but patient has 1 of the first 3 risk factors listed

• Known GBS-positive status in a previous pregnancy.

Intrapartum antibiotics are not required for GBS carriers who are having a planned cesarean delivery with intact membranes and no labor.[28]

The goals of pharmacotherapy are to reduce morbidity and to prevent complications.

Class Summary

Empiric antimicrobial therapy must be comprehensive and should cover all likely pathogens in the context of the clinical setting. Therapy should begin immediately after blood cultures are obtained.

Penicillin G (Pfizerpen)

Interferes with synthesis of cell wall mucopeptide during active multiplication, resulting in bactericidal activity against susceptible microorganisms. Penicillin remains the drug of choice for group B streptococcal infection.

Ampicillin (Ampi, Omnipen, Penglobe)

Interferes with synthesis of cell wall mucopeptide during active multiplication, resulting in bactericidal activity against susceptible microorganisms. Ampicillin  remains a drug of choice for group B streptococcal infection

Ceftriaxone (Rocephin)

Third-generation cephalosporin that arrests bacterial cell wall synthesis, inhibiting bacterial growth. Primarily active against skin flora, including most streptococcus and stahylococcus species. It also provides good gram-negative coverage

Ceftriaxone is alternative therapy to penicillin for group B streptococcal infection. Ceftriaxone would be effective for meningitis

Cefazolin (Ancef, Kefzol, Zolicef)

First-generation semisynthetic cephalosporin that arrests bacterial cell wall synthesis, inhibiting bacterial growth. Primarily active against skin flora, including Staphylococcus aureus. Typically used alone for skin and skin structure coverage. IV and IM dosing regimens are similar.

Cefazolin is alternative therapy to penicillin for group B streptococcal infection. Cefazolin would not be effective for meningitis.

Vancomycin (Vancocin)

Potent antibiotic directed against gram-positive organisms. Useful in the treatment of septicemia and skin structure infections. Indicated for patients who cannot receive or who have failed to respond to penicillins and cephalosporins or who have infections with resistant staphylococci.

To avoid toxicity, the current recommendation is to assay vancomycin trough levels after the third dose drawn 0.5 h prior to next dosing. Use creatinine clearance to adjust dose in patients diagnosed with renal impairment.

May need to adjust dose in renal impairment. Vancomycin is the initial treatment of choice for group B streptococcal infection in the penicillin-allergic individual.

Clindamycin (Cleocin)

Not for use as initial therapy because a small percent of group B streptococci will be resistant to clindamycin. Should not be used for endocarditis, bacteremia, or meningitis. If bacteria are sensitive, it can be used for pneumonia, osteomyelitis, and soft tissue infection. May also be useful as oral therapy to follow a course of parenteral therapy or if access becomes an issue.

Gentamicin (Gentacidin, Garamycin)

Aminoglycosides show synergy when used with penicillin for group B streptococcus. In neonates, the ill patient with sepsis and in certain situations, such as endocarditis, adding an aminoglycoside as a second drug may be helpful. The possible benefit must be weighed against the toxicity of renal and eighth nerve dysfunction, particularly in elderly people. The benefit of 2-drug therapy for group B streptococci has not been proven in terms of a better clinical outcome compared to penicillin therapy alone. The aminoglycoside needs to be tested against the isolate because only sensitive isolates can provide synergy.

Both chemoprophylaxis and immunoprophylaxis have been studied as a means to prevent group B streptococcal infection in neonates.

Although a group B streptococcal vaccine to prevent infection in women of childbearing age has been studied, an FDA–licensed vaccine is not yet available. Investigational vaccine studies are underway.

Chemoprophylaxis has been shown to be efficacious in neonates. A significant decline in neonatal infections over the past decade may be a result of this national standard.

The only approach for preventing group B streptococcal infection in nonpregnant adults is to adhere to infection control practices, as a significant number of these infections are nosocomial. The percentage of infections that can be prevented is unknown, as single nosocomial cases are common but a clustering of cases is rare.

Group B streptococcal infection in healthy women is usually amenable to therapy without major sequelae.

Neonatal infection, which still results in significant morbidity and mortality, has become less common and is more likely to have a better outcome because of chemoprophylaxis and early recognition of infection in infants.

Group B streptococcal infection in the nonpregnant adult carries a high risk for morbidity and mortality, even with early and appropriate therapy. The prognosis may be improved with a high index of clinical suspicion, initiation of early therapy after cultures are obtained, and procurement of an appropriate surgical opinion and adequate surgical intervention, when necessary.

Group B streptococcal infection in healthy women carries an excellent prognosis. In neonates, the infection carries a better prognosis than it once did but still results in significant morbidity and mortality. Nonpregnant adults with group B streptococcal infection are typically elderly with comorbid conditions; therefore, high mortality rates are inherent in those who develop infection.

Nonpregnant adults who survive group B streptococcal infection typically retain the underlying risk factor that originally placed them at risk for infection; therefore, the long-term prognosis in these patients is still poor.