Group B Streptococcus (GBS), also known as Streptococcus agalactiae, is best known as a cause of postpartum infection and as the most common cause of neonatal sepsis. This organism is also causes infection in nonpregnant adults. Group B streptococcal infection in healthy adults is extremely uncommon, except in young and middle-aged women, and is almost always associated with underlying abnormalities, with diabetes most commonly associated with infection in some series.
The GBS organism colonizes the vagina, GI tract, and the upper respiratory tract of healthy humans. GBS infection is almost always associated with underlying abnormalities. In elderly persons aged 70 years or older, GBS infection is strongly linked with congestive heart failure and being bedridden.
Signs and symptoms of GBS infection include the following:
See Clinical Presentation for more detail.
Examination in patients with GBS infection may demonstrate the following findings:
Lab tests
Laboratory studies in a patient with suspected GBS infection may include the following:
Imaging tests
The following imaging studies may be obtained in a patient suspected of having GBS infection:
Procedures
The following are procedures that may be performed in cases of suspected GBS infection:
See Workup for more detail.
Pharmacotherapy
GBS infection is primarily managed with antibiotics, including the following:
Penicillin, ampicillin, or vancomycin remains the treatment of choice for endocarditis.
If addition of an aminoglycoside to penicillin or ampicillin is under consideration to treat GBS infection, it is important to test for aminoglycoside sensitivity, because synergy is not observed if the organism is not sensitive to aminoglycosides. Keep in mind that group B streptococcal isolate can be resistant to one aminoglycoside and sensitive to another.
Surgery
Although medical therapy should cure many GBS infections, those involving skin, soft tissue, and bone may not be cured with antibiotics alone and may require surgical intervention, such as the following:
See Treatment and Medication for more detail.
Group B Streptococcus, also known as Streptococcus agalactiae, was once considered a pathogen of only domestic animals, 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 outcome of group B streptococcal infection in nonpregnant adults.
Group B streptococci colonize the vaginal and gastrointestinal tracts in healthy women, with carriage rates ranging from 15%-45%. Neonates can acquire the organism vertically in utero or during delivery from the maternal genital tract. Although the transmission rate from mothers colonized with S agalactiae to neonates delivered vaginally is approximately 50%, only 1-2% of colonized neonates go on to develop invasive group B streptococcal disease.[1]
Group B streptococcal neonatal sepsis is rare, but it is more common in the setting of prematurity and prolonged rupture of the membranes. Because of the ubiquity of S agalactiae colonization in women and the rarity of group B streptococcal 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 group B streptococcal disease is divided into early and late disease. Early group B streptococcal neonatal sepsis often presents within 24 hours of delivery but can become apparent up to 7 days postpartum. No specific clinical features differentiate early group B streptococcal disease from that caused by other pathogens. Pneumonia with bacteremia is common, while meningitis is less likely.
Late group B streptococcal neonatal sepsis is defined as infection that presents between one week postpartum and age 3 months. Late disease commonly involves group B Streptococcus serotype III, typically characterized by bacteremia and meningitis.
The absence of antibody to group B streptococci in infants is a risk factor for infection. Because antibodies to group B streptococci provide protection against disease in animal models, there is an ongoing interest in vaccination as an approach for reducing the incidence of group B streptococcal colonization in healthy women. Vaccine development was once promising, but shifting serotypes of group B streptococci 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 emotion and possible litigation associated with vaccination during pregnancy.
The current approach to the prevention of group B streptococcal infection in pregnancy approach requires intrapartum antimicrobial prophylaxis in term women with culture evidence of recent vaginal or rectal group B streptococcal infection. This has become a national standard owing to efforts by the Centers for Disease Control and Prevention (CDC) in 1995.[2] Women without a known group B streptococci status delivering before 37 weeks' gestation with premature rupture of the membranes or intrapartum fever are also candidates for intrapartum antimicrobial prophylaxis. Penicillin or ampicillin is the initial approach. Clindamycin and erythromycin are standard in individuals with penicillin allergy, but group B streptococci are no longer always sensitive to these two drugs.
Only in the last 3 decades has the role of group B streptococci as a serious pathogen in the nonpregnant adult been well defined. Numerous studies have allowed description of the clinical spectrum of disease, including clinical features, risk factors, therapy, and outcomes.
S agalactiae infection is extremely rare in healthy individuals and is almost always associated with underlying abnormalities. Among published series, diabetes mellitus and malignancy are consistently the most common underlying diseases associated with infection.[3] Other conditions associated with group B streptococcal infection in adults include cardiovascular and genitourinary abnormalities, neurologic deficits, cirrhosis, steroids, AIDS, renal dysfunction, and peripheral vascular disease. Relapse is not uncommon, with approximately 5% of nonpregnant adults eventually experiencing a second episode of group B streptococcal disease.[4]
Group B streptococcal infection in elderly people (≥70 y) is strongly linked to congestive heart failure and being bedridden, with urinary tract infection, pneumonia, and soft-tissue infection as the most common manifestations of infection. Neurologic illness is associated with pneumonia in elderly people, possibly due to aspiration of group B streptococci from the upper respiratory tract. Nosocomial group B streptococcal infection was 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 found commonly 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 also is observed in wound and soft tissue cultures in the absence of obvious infection. Determining the acquisition and transmission of S agalactiae can be puzzling, as it is very invasive but produces little inflammation at the entry site.
Primary group B streptococcal bacteremia without an obvious source is a common presentation in adults. While one series suggests that group B streptococcal bacteremia is low-grade and easily controlled with little morbidity, other authors suggest that the clinical presentation may be that of classic sepsis with shock and may carry a high mortality. 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 group B streptococcal disease and are observed in both pregnant and nonpregnant adults. Other presentations of group B streptococcal infection include pneumonia, skin and soft-tissue infections, septic arthritis, osteomyelitis, meningitis, peritonitis, and endo-ophthalmitis.
Group B Streptococcus remains sensitive to penicillin and ampicillin and was once also sensitive to cefazolin, erythromycin, and clindamycin. Although penicillin is the treatment of choice, it is unclear whether penicillin therapy provides a better outcome than other antibiotics.
S agalactiae is a gram-positive coccus that, when cultured on sheep blood agar, forms glistening gray-white colonies with a narrow zone of beta hemolysis. It is an invasive encapsulated organism capable of producing severe disease in immunocompromised hosts. Group B streptococcal infection in the absence of associated comorbid medical conditions is rare.
The virulence is 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.
Group B streptococci colonize the vagina, gastrointestinal tract, and the upper respiratory tract of healthy humans. The portal of entry is not apparent, but possible areas include the skin, genital tract, urinary tract, and respiratory tract.
United States
Group B streptococcal neonatal sepsis occurs in 1.8-3.2 per 1000 live births. In 2005, early group B streptococcal neonatal sepsis was observed in 0.35 per 1000 births, while late sepsis was observed in 0.33 per 1000 births.[5] The incidence of early disease has decreased over the past decade, likely because of the CDC guidelines for the prevention of neonatal colonization with group B streptococci.
While the incidence of group B streptococcal 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.[5] A recently published study of surveillance data from 10 states found that the incidence of group B streptococcal infection in persons aged 15-64 years increased from 3.4 per 100,000 population in 1999 to 5 per 100,000 in 2005. In adults aged 65 years and older, the incidence increased from 21.5 per 100,000 population in 1999 to 26 per 100,000 in 2005.[5]
International
The role of group B streptococci in the developing world is not well defined. Carriage rates and serotypes in women in underdeveloped countries are similar to those observed in the industrial world. However, for unknown reasons, early group B streptococcal disease in infants is not documented in less-developed countries.
Group B streptococcal disease results in significant mortality in both neonates and adults. While the mortality rate ranges from 9-47% in published reports, most studies find it to be approximately 20%.[4] 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 group B streptococcal infection may not reflect the organism itself but the predisposing condition or conditions that put the individual at risk for group B streptococcal infection.
The mortality rate of neonatal group B streptococcal infection is much less than that in nonpregnant adults. An increasing awareness of group B streptococcal infection in infants has led to improved outcomes in recent years.
Postpartum group B streptococcal infection is associated with a low mortality rate because the group at risk is composed of healthy young or middle-aged women.
Group B streptococcal infection is more common in African Americans than in whites and is much more common in older African Americans than in older whites. These differences are probably due to socioeconomic differences rather than race.
Young and middle-aged women who undergo obstetrical and gynecological manipulation are at an increased risk of group B streptococcal infection.
Among nonpregnant patients, group B streptococcal infection has no sexual predilection.
The mean age for group B streptococcal infection is 64 years.
A bimodal distribution is well recognized. Young and middle-aged healthy women with group B streptococcal infection secondary to obstetrical or gynecological manipulation is one group, while the second group is elderly persons with group B streptococcal infection as a complication of preexisting illness.
Group B streptococcal infection in healthy adults is extremely uncommon, except in young and middle-aged women. Group B streptococcal infection is almost always associated with underlying abnormalities, with diabetes most commonly associated with infection in some series. This association, which the authors have observed over the last 25 years, is unexplained. Malignancy was the most common association in a series from an institution with a large population of patients with cancer. Cardiovascular and genitourinary abnormalities have also been identified as major factors that predispose to group B streptococcal acquisition. Other conditions associated with group B streptococcal infection in adults include neurologic deficits, cirrhosis, steroids, AIDS, renal dysfunction, and peripheral vascular disease. In elderly people aged 70 years or older, group B streptococcal infection is strongly linked with congestive heart failure and being bedridden.
Group B streptococcal pneumonia is rare and has few unique features. It is observed in elderly people with diabetes and with neurologic deficits and may result from aspiration of group B streptococci that colonize the upper airway. In one series, group B streptococcal pneumonia appeared to be associated with a high rate of bacteremia.
Group B streptococcal meningitis, a common manifestation of neonatal infection, is uncommon in adults. It is almost always associated with anatomical abnormalities contiguous with, or of, the CNS, usually as a result of neurosurgery.
Group B streptococcal bacteremia is common. While 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 group B streptococcal disease in some studies.[4] Group B streptococcal pneumonia in elderly people has been associated with bacteremia. Endocarditis should always be strongly considered in cases of bacteremia without an identified source. Often, the diagnosis becomes obvious because group B streptococcal endocarditis is very destructive and frequently necessitates valve replacement for valve insufficiency.
Other manifestations of group B streptococcal infection include skin and soft-tissue infection, osteomyelitis, arthritis, discitis, and colonization of diabetic foot infections and decubitus ulcers. For an unclear reason, many patients who develop such manifestations have diabetes. Although medical therapy should cure many group B streptococcal infections, those involving skin, soft tissue, and bone may not be cured with antibiotics alone and may require surgical intervention. Group B streptococcal infections leading to necrotizing fasciitis and toxic shock syndrome have been documented.[4, 6]
Chorioamnionitis, endometritis, and the full spectrum of urinary tract infections (from asymptomatic bacteruria to cystitis and pyelonephritis with bacteremia) are observed with group B streptococcal infection. These are common complications often related to childbirth in young and middle-aged women. Urinary tract infections with group B streptococci also are observed in elderly men and women, often those with diabetes or genitourinary abnormalities.
Pneumonia in bedridden elderly patients with neurologic deficits and fever, shortness of breath, chest pain, pleuritic pain, or cough
Meningitis in the neurosurgical patient with fever, headache, nuchal rigidity, or confusion
Bacteremia, line-related infection, sepsis, or endocarditis in the patient with fever, malaise, confusion, chest pain, shortness of breath, myalgia, or arthralgia
Skin and soft-tissue infection, osteomyelitis, or septic arthritis in patients with diabetes or in elderly patients with fever, malaise, localized pain, cellulitis, arthralgia, arthritis, or weakness
Urinary tract infection or pelvic abscess in the postpartum woman or older man or woman with fever, dysuria, flank pain, or pelvic pain
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 diabetic or elderly patients with 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
Gram stain of an appropriate specimen is a useful first test. It can show early streptococcal infection.
Isolation of group B streptococci from blood, cerebrospinal fluid (CSF), and/or a site of local suppuration is the only method for diagnosing invasive group B streptococcal infection.
Group B streptococcal antigen may be detected in blood, CSF, and/or urine and may aid in diagnosis in certain circumstances.
Consider pneumonia in the elderly bedridden patient with fever and other appropriate symptoms and neurologic deficits. Radiographs may show infiltrate or effusion in such patients.
Consider meningitis in the neurosurgical patient with fever and other appropriate symptoms. CT scanning of the head may reveal an abscess or contiguous infection. Exclude increased intracranial pressure so lumbar puncture (LP) can be performed safely.
Consider bacteremia, endocarditis, and line-related sepsis in a patient with fever. Echocardiography may reveal vegetation or evidence of valve destruction.
In a patient who is elderly, bedridden, or diabetic with fever and appropriate symptoms, consider soft-tissue infection, osteomyelitis, discitis, 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 MRIs of the involved area may reveal phlegmon, abscess, or osteomyelitis.
In a postpartum woman or older man or woman with fever and appropriate symptoms, consider urinary tract infection and pelvic abscess. Ultrasonography of the genitourinary system or pelvis may reveal evidence of genitourinary obstruction or abscess. CT scans and MRIs may show evidence of obstruction or abscess.
Although rapid tests are available for assessment of maternal group B streptococcal colonization at labor, a study of two rapid tests by Daniels et al found that neither was sufficiently accurate to recommend their routine use in clinical practice. Of the two tests, polymerase chain reaction (PCR) proved significantly more accurate than optical immunoassay (OIA); nevertheless, when combined vaginal and rectal swab tests were used, PCR had a sensitivity of 84% (95% confidence index [CI], 79-88%) and a specificity of 87% (95% CI, 85-89%). 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 35-37 weeks' gestation is likely to be the most acceptable cost-effective strategy.[7]
Another study found that while intrapartum antibiotic prophylaxis was effective in preventing mother-to-newborn transmission of group B streptococcal colonization, prenatal cultures obtained from health care providers during routine care did not accurately predict the occurrence of infection found during labor.[8]
Schwope et al (2010) advise that, when collecting samples for group B Streptococcus screening during a pelvic examination, practitioners should collect the sample before using a bacteriostatic surgical lubricant. In a prospective cohort study in 168 patients, 20 patients tested positive for group B Streptococcus before the pelvic examination, but only 10 of those tested positive after the pelvic examination with a chlorhexidine-based surgical lubricant.[9]
Group B streptococcal pneumonia may require diagnostic and therapeutic thoracentesis if pleural effusion is present; empyema requires drainage by thoracentesis, chest tube, or surgery.
Group B streptococcal bacteremia, endocarditis, and line-related sepsis may require valve replacement because of destructive endocarditis.
Group B streptococcal soft-tissue infection, arthritis, osteomyelitis, discitis, and epidural abscess may require diagnostic aspiration and curative surgery. Necrotizing fasciitis and septic arthritis are surgical emergencies. Epidural abscess may require emergency surgery.
Group B streptococcal urinary tract infection or pelvic abscess may require aspiration with ultrasonography or CT scan guidance for a diagnostic tap to isolate the organism, to relieve obstruction, or to drain an abscess.
Group B streptococci are uniformly sensitive to penicillin and ampicillin. Although resistance to penicillin or ampicillin has not be documented, some isolated have shown minimum inhibitory concentrations (MICs) approaching the upper limits of susceptibility for some of the beta-lactam agents.[5] Group B streptococci have never been as exquisitely sensitive to penicillin as group A beta-hemolytic streptococci; therefore, the initial therapy for group B streptococcal infection has always been high-dose parenteral penicillin or ampicillin.
Penicillin or ampicillin plus an aminoglycoside has demonstrated synergy but has not been shown to provide a better clinical outcome than penicillin or ampicillin alone. Testing for aminoglycoside sensitivity is important because synergy is not observed if the organism is not sensitive to aminoglycosides. Keep in mind that given group B streptococcal isolate can be resistant to one aminoglycoside and sensitive to another.
While 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 over 4800 group B streptococcal isolates found that 32% were resistant to erythromycin, 15% were resistant to clindamycin, and 99% of clindamycin-resistant strains were also resistant to erythromycin.[5] As a result, sensitivity testing is important before these agents are used. Oral clindamycin remains an excellent agent to follow a course of parenteral therapy for bone, soft-tissue, and lung infections if the isolate is susceptible.
Because of possible resistance with clindamycin, vancomycin remains the initial treatment of choice for group B streptococcal infection in patients who are allergic to penicillin. Penicillin, ampicillin, or vancomycin remains the treatment of choice for endocarditis. While vancomycin may be adequate in group B streptococcal meningitis in patient 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 group B streptococcal endocarditis.
While fluoroquinolones appear to have efficacy against isolates of group B streptococci, resistance to fluoroquinolones has recently been reported.[10]
Similarly, linezolid, a new antibiotic with efficacy for aerobic gram-positive cocci, should have activity against group B streptococci. It is available in parenteral or oral form. However, no clinical studies have evaluated linezolid in group B streptococcal infections.
Surgical opinion and intervention is important.
Pneumonia may require empyema drainage.
Endocarditis, bacteremia, and sepsis may require heart valve replacement.
Soft-tissue infection, septic arthritis, osteomyelitis, discitis, and epidural abscess often require surgery combined with parenteral antibiotics for cure.
Necrotizing fasciitis and septic arthritis are surgical emergencies.
Epidural abscess may require emergency surgery.
Urinary tract infection and pelvic abscess may require relief of genitourinary obstruction and abscess drainage for cure.
Group B streptococcal infection may require various consultations for an optimal outcome. An infectious disease specialist is often helpful in choosing the antibiotic and duration of therapy. Appropriate surgical support is critical for a good outcome.
Pneumonia may require a pulmonologist or surgeon for empyema drainage.
Bacteremia, endocarditis, and line-related sepsis may require a cardiovascular surgeon for valve replacement.
Soft-tissue infection, osteomyelitis, epidural abscess, discitis, and arthritis require a rheumatologist for arthrocentesis and an orthopedic surgeon or neurosurgeon for possible surgical opinion and intervention.
Urinary tract infection or pelvic abscess may require a urologist or gynecologist for surgical opinion and possible relief of obstruction and abscess drainage.
The Royal College of Obstetricians and Gynaecologists (RCOG) has issued guidelines on the prevention of group B streptococcal disease in preterm labor.[29, 30]
For prevention of early-onset GBS (EOGBS) infection, offer intrapartum intravenous antibiotics (penicillin G, a cephalosporin in women with penicillin allergies, or vancomycin in women with severe penicillin allergies) in the following scenarios:
Although RCOG recommends against universal GBS screening for all pregnant women, if performed, testing should occur at 35-37 weeks of pregnancy or 3-5 weeks prior to the anticipated delivery date (eg, 32-34 weeks’ gestation in women with twins). In particular, this may apply to women who have had GBS in a previous pregnancy, because results may guide decision-making about the need for intrapartum antibiotics.
Intrapartum antibiotics are not required for GBS carriers who are having a planned cesarean with intact membranes and no labor.
The goals of pharmacotherapy are to reduce morbidity and to prevent complications.
Clinical Context: 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.
Clinical Context: 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.
Clinical Context: 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.
Clinical Context: Oritavancin is lipoglycopeptide antibiotic that inhibits cell wall biosynthesis and disrupts bacterial membrane integrity that leads to cell death. It is indicated for treatment of acute bacterial skin and skin structure infections caused by gram-positive bacteria including S aureus (including methicillin-susceptible S aureus and MRSA), S pyogenes, S agalactiae, S dysgalactiae, S anginosus group (S anginosus, S intermedius, S constellatus) and E faecalis (vancomycin-susceptible isolates only).
Clinical Context: Lipoglycopeptide antibiotic that is a synthetic derivative of vancomycin. Inhibits bacterial cell wall synthesis by interfering with polymerization and cross-linking of peptidoglycan. Unlike vancomycin, telavancin also depolarizes the bacterial cell membrane and disrupts its functional integrity. Indicated for complicated skin and skin structure infections caused by susceptible gram-positive bacteria, including Staphylococcus aureus (both methicillin-resistant and methicillin-susceptible strains), Streptococcus pyogenes, Streptococcus agalactiae, Streptococcus anginosus group, and Enterococcus faecalis (vancomycin-susceptible isolates only).
Clinical Context: Dalbavancin is lipoglycopeptide antibiotic that prevents cross-linking by interfering with cell wall synthesis. It is bactericidal in vitro against Staphylococcus aureus and Streptococcus pyogenes at concentrations observed in humans at recommended doses. It is indicated for treatment of acute bacterial skin and skin structure infections caused by Gram-positive bacteria including Staphylococcus aureus (including methicillin-susceptible and methicillin-resistant S aureus [MRSA]), S pyogenes, Streptococcus agalactiae, and the Streptococcus anginosus group (including S anginosus, S intermedius, S constellatus).
Clinical Context: Tedizolid is an oxazolidinone antibiotic indicated for skin and skin structure infections caused by susceptible isolates of Gram-positive bacteria including Staphylococcus aureus (including methicillin-resistant [MRSA] and methicillin-susceptible [MSSA] isolates), Streptococcus pyogenes, S agalactiae, S anginosus Group (including S anginosus, S intermedius, and S constellatus), and Enterococcus faecalis. Its action is mediated by binding to the 50S subunit of the bacterial ribosome resulting in inhibition of protein synthesis.
Clinical Context: 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.
Clinical Context: 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.
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.
Both chemoprophylaxis and immunoprophylaxis have been studied as a means to prevent group B streptococcal infection in neonates.
While a group B streptococcal vaccine to prevent infection in women of childbearing age has been studied, an FDA–licensed vaccine in 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 of 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.