Transcript Group B Streptococcus

Group B Streptococcus
Streptococcus agalactiae
Reproductive Infectious Disease Seminars
September 28, 2004
Natali Aziz, MD, MS
Reproductive Infectious Disease and Maternal-Fetal Medicine Fellow
Department of Obstetrics, Gynecology and Reproductive Sciences
University of California, San Francisco
Microbiology
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Gram-positive cocci
Chains
Encapsulated
Non-motile
Facultative anaerobes
Lactic acid production
Multiple nutritional
requirements
• 1-4 mm diameter, greywhite, flat, mucoid
• Selective Broth Media
(SBM) or Lim broth
http://medicine.ucsd.edu/NizetLab
• β-hemolysis
Classification
– RBCs surrounding the colony are
completely lysed
– “Hemolysin" toxins
– Orange pigment
– Narrow hemolysis zones
– CAMP factor enhances hemolysis
• Carbohydrate Antigens (C
substance)
– Lancefield Group B
– Group specific antigen
• Polysaccharide Capsule Serotypes
– 150 oligosaccharide subunits with
mono-, di-, tri- side chains
– Ia, Ib, II-VIII
– III and V completely sequenced
http://medicine.ucsd.edu/NizetLab
Epidemiology
• Humans (and cattle)
• Genitourinary and
gastrointestinal tracts in
adults
• Upper respiratory tract
in young infants
• Pregnant women,
neonates, and nonpregnant adults
Bovine Mastitis
Epidemiology
Pregnant Women and Neonates
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Pregnant women:
20-30% rectovaginal colonization
Pregnant women infection 0.3 per 1000
live births
50-70% infants born to colonized
mothers will become colonized
1-2% infants develop early-onset
invasive disease (EOID)1
Heavy colonization associated with PTD
Colonization rates differ by ethnic
groups, geographic locales, and age in
pregnant women2
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Risk factors neonatal EOID:
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GBS maternal colonization (x29)
Maternal age < 20 yo
African American race
Heavy colonization (>105 cfu/ml)
Low anti-GBS capsular Abs
Parity
Intrapartum fever, chorioamnionitis,
GBS bacteriuria, prematurity,
prolonged rupture of membranes
(>18 hours), PPROM, prior infant
with GBS infection
– NY Hispanics, Af AM> Caucasians>
Hispanics, Asians
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Serotypes differ by geographic locales in
pregnant women
– Japan VI, VIII
– Denmark VIII
1Prevention
2Regan,
of perinatal group B streptococcal disease: a public health perspective. MMWR ;45(RR-7):1-24.
et al. The epidemiology of GBS colonization in pregnancy. Obstet Gyn 1991;77:604-10.
Epidemiology
Non-pregnant Adults
• Emergence in 1980-90’s
– Atlanta: Incidence 2.4, 4.4,
5.9 per 100,000 in 1982,
1990, 19921
– > 7600 adult GBS infections
annually2
• ?Virulent strains
• ?Chronic diseases / more
immunosuppression
• ? Loss of barrier of
protection in chronically
colonized site
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• 29% serotype V (<Ia, Ib, III)
• Risk factors
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African American Race
Increasing age
Institutionalization
Chronic illness
HIV
Alcoholism
Trauma
• Bimodal Distribution
– Mid 20’s and mid 60’s
• Mortality 15-38%
Farley, et al. A population-based assessment of invasive disease due to group B streptococcus in non-pregnant
adults. NEJM 1993;328:446.
2 Zangwill, et al. GBS disease in the US, 1990:report from a multi-state active surveillance system. MMWR CDC
Surveil Sum 1992;41:25.
Epidemiology
Adult GBS infection: ¾ of invasive disease and 90% of mortality in US
Up To Date: Group B streptococcal infections in non pregnant adults.
Adult Clinical Manifestations
• Pregnant Women Infections
– Urinary tract infections
• Asymptomatic bacteriuria
• Cystitis
• Pyelonephritis
– Chorioamnionitis
• Heavy 2nd trimester colonization
– Puerperal sepsis
(<12 hours post delivery)
– Endometritis
(> 24 hours after delivery)
• Non-pregnant Adult Infections
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Skin and soft tissue (15-40%)
Bacteremia (30-40%)
UTIs (5-15%)
Pneumonia (6-12%)
Bone and joint(2-15%)
Cardiac (2-9%)
• Endocarditis on native valves, Lsided
– CNS (4%)
– Toxic shock-like syndrome
– Meningitis, endocarditis,
abdominal abscess, necrotizing
fasciitis
Treatment: PCN G; vancomycin if allergic; gentamicin for synergy in endocarditis
Neonatal Clinical Manifestations
• Acquired in-utero or at delivery
• Serotypes III, Ia, >II, V account
for 85% of infections in infants
• Early-onset disease:
– Up to 7th day of life
– Usually within 12-24 hours of
life
– Serotypes I and II
– Bacteremia
– Sepsis
– Pneumonia
– Meningitis (10-15%)
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Late-onset disease:
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7-89 days old
50% attributable to vertical transmission
Serotype III
Meningitis (35%)/seizures
Pneumonia, septic arthritis,
osteomyelitis, cellulitis, adenitis, and
others
– Current Treatment
• Amp/Gent PCN G once dx confirmed
– PCN at high dose as has higher
MIC; more selective
– Resistance to erythromycin,
clindamycin, TMP-SMX, and
gentamicin
• IVIG and GBS hyperimmune globulin
GBS Neonatal Infection
Incidence Trends1
Incidence of EOID
1990: 1.8 per 1000 live births
1999: 0.5 per 1000 live births
2000: 0.6 per 1000 live births
1Prevention
of perinatal group B streptococcal disease: revised guidelines from CDC. MMWR 2002;51(RR-11):1-24.
Guidelines for Prevention of
Perinatal GBS Disease
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Schrag, et al 2002
– Antenatal screening strategy prevented 55% more cases of EOID than riskbased approach
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Prevention of Perinatal GBS Disease: Revised Guidelines form CDC. MMWR 2002;51 (RR-11):1-24.
Guidelines for Prevention of
Perinatal GBS Disease
Prevention of Perinatal GBS Disease: Revised Guidelines form CDC. MMWR 2002;51 (RR-11):1-24.
Intrapartum Antibiotic Prophylaxis
Prevention of Perinatal GBS Disease: Revised Guidelines form CDC. MMWR 2002;51 (RR-11):1-24.
Pathogenesis
Neonatal Disease
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Vaginal colonization in pregnant women
– Adherence to epithelial cells and
resisting mucosal immune defenses
Fetus aspirates infected fluid as organism
ascends into the amniotic cavity by
penetration of placental membranes or at
time of delivery with ROM
Bacteria enter the fetal lung through
aspiration of infected amniotic fluid.
Pneumonia with lung epithelial and
endothelial cell injury are characteristic of
early onset disease,
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cytotoxic properties of ß-hemolysin and the
influx of host neutrophils.
GBS invade alveolar epithelial and
pulmonary endothelial cells within
membrane-bound vacuoles
Newborn infants, particularly premature
infants, have fewer alveolar macrophages
than adults and exhibit poor neutrophil
chemotaxis.
GBS are inefficiently phagocytosed in the
absence of opsonization by specific antibody
or complement, diminished in neonatal
serum.
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Polysaccharide capsule of GBS has a marked
inhibitory effect on phagocytic clearance by
preventing complement deposition on the
bacterial surface.
Components of GBS surface protein C may
both retard opsonization and decrease killing
of GBS taken up by neutrophils
Cell wall-associated components of
circulating GBS induce a sepsis syndrome
characterized by severe systemic hypotension,
pulmonary hypertension, hypoxemia and
acidosis.
Effects of a host inflammatory response
mediated by release of tumor necrosis factor
(TNFalpha), interleukins, prostaglandins and
thromboxane.
Bloodstream dissemination allows GBS to
reach multiple body sites, and invasion of
brain microvascular endothelial cells may be
the first step in production of meningitis.
Pathogenesis
Fig. 1. Stages in the molecular and cellular pathogenesis of neonatal group B Streptococcal (GBS) infection.
Doran, Kelly S. & Nizet, Victor. Molecular pathogenesis of neonatal group B streptococcal infection:
no longer in its infancy. Molecular Microbiology 2004;54:23-31.
Pathogenesis
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Maximal cell adherence at acidic pH of vaginal mucosa
Selective fibronectin adherence mediated by RogB and FbsA
Rib protein expressed by invasive isolates
Traverses chorionic, not amniotic, cells by generation of oxygen radicals
and PGE2
– Suspected association with membrane rupture and preterm delivery
• Infant lung damage: intracellular invasion, direct cytolytic injury, and
damage induced by the inflammatory response
• Loss of pulmonary and blood-brain barrier integrity loss due to βhemolysin/cytolysin promoting IL-8 release
• Effects can be neutralized by major surfactant phospholipid constituent
• CAMP factor triggers cell lysis by creating discrete pores
• Conserved GBS surface proteins (ScpB, Sip, BSP)
Virulence Factor
GBS Surface Polysaccharide Capsule
• Antiphagocytic properties
• Capsule-deficient mutants
diminished virulence in animal
models
• Sialic acid residues on capsule
inhibit the binding of opsonicallyactive C3 component of
complement to the cell surface
– blocking activation of the
alternative pathway
• Transplacental passage of typespecific anticapsular IgG antibody
from mother to infant is an
important protective factor against
invasive disease
http://medicine.ucsd.edu/NizetLab
Virulence Factor
GBS β-hemolysin
• Cytotoxic to pulmonary epithelial and endothelial cells
– Pulmonary injury and alveolar protein exudate in early-onset
pneumonia
• Activity is blocked by surfactant phospholipid
– Increased risk of premature, surfactant-deficient neonates for severe
pneumonia
• Induces cytokine release and nitric oxide production in
macrophages
– Stimulate elements of the sepsis cascade
Virulence Factor
C5a-peptidase
• Cleaves and inactivates the complementderived neutrophil chemoattractant C5a
• C5a-peptidase-deficient mutants are more
rapidly cleared from the lungs of infected
animals when compared to the isogenic wildtype strain
Immune Mechanism
and Pregnancy
• Smith, et al 2001
– Purpose:
• To evaluate functional capacity of granulocytes and monocytes
from pregnant and non-pregnant women in relation to GBS
colonization status
– Methods:
• Engulfment of fluorescent GBS by peripheral phagocytes in GBS
colonized and uncolonized women measured by flow cytometry
– Conclusions:
• Monocytes from pregnant, GBS colonized women engulfed more
GBS and released significantly more superoxide into the
extracellular milieu than did granulocytes from the same women.
• Unlikely effective defense mechanism against intracellular bacteria
• Components of innate immune system may function suboptimally,
contributing to the colonization process by GBS
Smith JM, et al. Differences in innate immunologic response to group B streptococcus between colonized and
noncolonized women. Infect Dis Obstet Gynecol 2001;9:125-32.
Immune Mechanism
and Pregnancy
• Campbell, et al 2000
– Objective:
• To investigate relationship between
serum concentration of GBS capsular
polysaccharide-specific IgG,
colonization status, race or ethnicity,
and age in pregnant women
– Results/Conclusion:
• Women aged <20 yo had lowest median
serum concentrations of CPS IgG
• Colonization with GBS may elicit a
systemic immune response, with
increased prevalence of CPS IgG with
increasing age.
• Low IgG levels in teenagers may
account for increased risk of GBS
disease in neonates born to these
Figure 4. Distribution of group B streptococcal capsular
polysaccharide–specific immunoglobulin G (Ig) G
concentrations in delivery sera of 294 colonized women
categorized by age. Distribution is illustrated as the
percentage of each age group with less than 0.5 (white
bars), 0.5–1.0 (dotted bars), or more than 1.0 (black bars)
mcg/mL of specific IgG.
Campbell JR, et al. GBS colonization and serotype-specific
immunity in pregnant women at delivery. Obstet Gyn 2000
96:498-503.
Diagnosis and Screening
• Culture– Gold Standard
– Selective broth medium (SMB or
Lim Broth)
• PCR (Berger, et al 2000)
– Comparable in sensitivity to
culture in extremely controlled
laboratory environment
– Limited studied of clinical
practice
• Immunoassay
– Enzyme and Optical
– Poor sensitivity
– Antigen detection may assist with
diagnosis of CSF infection
Bergeron MG, et al. Rapid detection of GBS in pregnant
women at delivery. NEJM 2000;343:175.
Rapid Screening: Clinical Experience
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• Objectives
– To compare the efficacy of the
rapid optical immunoassay
(OIA) and real-time
polymerase-chain reaction
(PCR) screening techniques to
the standard enrichment broth
culture for the detection of
GBS colonization in pregnant
women during labor.
– To evaluate real-time PCR
screening technique in an
intrapartum setting.
– To reexamine prior OIA
performance studies
conducted at Stanford/Lucile
Packard Hospital
Methods
– Double vaginal swabs collected from
315 patients at time of presentation for
delivery
– OIA performed with one swab within
2 h of collection per our current stat
protocol.
– PCR performed on second swab-placed in buffer, 50 µl of which was
used for the real-time PCR protocol,
performed on a Cepheid Smartcycler
once every 24 h.
– Another 500 µl of buffer and swab
were incubated in Lim broth for
culture detection of GBS.
– For 75% of samples yielding
discrepant PCR and culture results,
another larger volume extraction and
subsequent amplification were done
using remaining cell eluate.
– Sensitivity/specificity/confidence
intervals calculated.
Rapid Screening: Clinical Experience
GBS vaginal colonization rate: 17.8%
SENS
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PPV
NPV
OIA
0.071
0.981
0.444
0.830
PCR
0.625
0.973
0.833
0.923
Alternate
PCR
0.821
0.973
0.868
0.962
Aziz N, et al. Comparison of OIA and PCR for GBS rapid intrapartum screening. Manuscript in preparation .
Rapid Screening: Clinical Experience
• Conclusions
– Rapid OIA technique is not a reliable method for GBS
screening in an intrapartum setting.
– Although real-time PCR technique is a more reliable
method than the rapid OIA technique for GBS screening in
an intrapartum setting, it was not as sensitive as Bergeron
findings in intrapartum setting.
– Real-time PCR technique may have a useful role in the
management of women whose GBS status is unknown at
time of presentation for delivery.
– Laboratory technique may significantly impact OIA results.
– “Research Method” tends to yield better results than “Routine
Laboratory” application for both techniques.
Immunoprophylaxis
• Maternal antibody against typespecific capsular polysaccharide
protective
– May not be sufficient and infants <
32 wks do not benefit from placental
transport of maternal IgG
• Limitations with current
guidelines
– Administration of unnecessary
antibiotics
– Late to care and unknown status
– RF strategy not good enough
– Antibiotic adverse effects
– Increased E coli Amp-resistance in
infants <1500gm
– No change in late onset disease
– Invasive (IV)
• Targets for vaccine
– Group B carbohydrate Ab’s not protective
(not virulent factor)
– Capsular polysaccharide confers
specificity except two cases
– Others: Sialic acid, protein antigens, Beta
C protein, Alpha C protein
• Vaccine Formulations
– Polysaccharide (CPS)
• Phase I study promising for serotype
III, even in pregnant patients
• Studies for Ia and II variable results
– Polysaccharide-protein conjugate
• Animal studies more immunogenic
with coupling
– Potential GBS protein vaccines
• Difficulty finding conservation
among serotypes
Immunoprophylaxis Challenges
• Proving vaccine efficacy is going to be very difficult.
– To demonstrate an 80% reduction in risk, from 0.5 per 1000 to 0.2 per 1000 births with
an alpha of 0.05 and beta of 0.8, will require enrollment of 125,000 women who deliver
babies during the follow-up period.
– Will likely need an even larger number, since some women may not end up (or stay)
pregnant
– Will require large and expensive trial.
• Organisms such as pneumococcus and GBS have polysaccharide
antigens that are poor immunogens.
– Coupling them to haptens like pertussis or tetanus toxoids often works for individual
polysaccharides,
– However, when combining into polyvalent vaccines, the responses are often
inconsistent.
– Constructing a vaccine to all of the common serotypes (now at least Ia, Ib, II, III, and V)
is a challenging task.
– Antigen drift in the population of colonizing organisms may make today's vaccine
obsolete tomorrow, as those serotypes disappear and type VIII and/or others become
predominant.
• Women whose infants are at greatest risk are characterized by heavy
GBS colonization and the absence of effective opsonizing antibody.
– The latter is clearly not a consequence of a lack of exposure to the antigens -- they're
heavily colonized, after all; likely that these women may have some immunogenetic
impediment to development of protective antibodies, and it is not clear that they would
do that better after exposure to a vaccine than they do after natural exposure.