Prevalence of type-specific group B streptococcal antibody in pregnant women

Risk factors for group B streptococcal disease in neonates of mothers with negative antenatal testing

OBJECTIVE

The aim of this study was to identify risk factors for early-onset group B Streptococcus (EOGBS) disease in neonates of mothers with negative antenatal screening.

STUDY DESIGN

We performed a retrospective cohort study of neonates born to mothers with negative antenatal GBS screening between 2002 and 2012. Our primary outcome was EOGBS infection. We used multivariable logistic regression to assess factors associated with EOGBS.

RESULTS

EOGBS was confirmed in 492 of the 179 818 neonates that met the study inclusion criteria. Risk factors for EOGBS included black race (reference: white, odds ratio (OR) =1.81 (95% confidence interval: 1.43, 2.31)), maternal age <18 years (reference: >35 years, OR=2.63 (1.54, 4.51)) and maternal age 18 to 35 years (reference: >35 years, OR=1.94 (1.30, 2.88)).

CONCLUSION

Maternal age <18 years and black race were the strongest predictors of EOGBS. Further research investigating contributors to the discordance between screening results and neonatal outcomes in these populations is needed.

Group B streptococcal disease in infants: progress in prevention and continued challenges

The burden of early-onset disease caused by group B Streptococcus (GBS) has decreased dramatically in the United States over the past 20 years. Universal culture-based screening at 35 to 37 weeks gestational age and use of intrapartum antibiotic prophylaxis are the cornerstones of prevention measures that have led to this decline. GBS, however, remains the leading cause of early-onset neonatal sepsis in the United States. Revised guidelines for prevention of perinatal GBS are planned for issuance in 2010. This article discusses implementation challenges for clinicians caring for pregnant women and newborns and presents an updated algorithm for neonatal management.

Cervical secretions in pregnant women colonized rectally with group B streptococci have high levels of antibodies to serotype III polysaccharide capsular antigen and protein R

Group B streptococci (GBS) colonizing the female genital tract will often infect newborn infants during delivery. In 200 pregnant women studied, 14% were colonized with GBS in the cervix, 12% in the rectum, and 9% in both cervix and rectum. We have previously reported that antibody levels to GBS serotypes Ia, II, and III in sera and cervical secretions were increased in women colonized in the rectum and/or cervix, when analyzed by a whole-cell ELISA. Here, we report the levels of antibodies to GBS serotype III capsular polysaccharide antigen (CPS III) and to protein antigen R4, which are present in most GBS III strains. Compared to culture-negative women, the group of women colonized rectally had markedly elevated levels of immunoglobulin (Ig)A and IgG antibodies in cervical secretions to both CPS III and protein R4 (P < 0.01 and P < 0.001, respectively). In sera, the corresponding differences between culture-negative and culture-positive women were less pronounced, or not present. In contrast to antibody levels to whole-cell GBS, antibody levels to CPS III and protein R4 in cervical secretions were not significantly increased in women colonized only in the cervix, except that IgA antibodies to protein R4 were slightly elevated (P < 0.05). These findings suggest that capsular type-specific polysaccharides and protein R4 in a mucosal vaccine might induce protective antibodies against GBS colonization of the uterine cervix.

Safety and immunogenicity of a tetravalent group B streptococcal polysaccharide vaccine in healthy adults

Proposed strategies for prevention of neonatal group B streptococcal (GBS) infection have included active immunization of pregnant women and passive immunization of high-risk infants with hyperimmune GBS globulin derived from vaccinated plasma donors. To explore the feasibility of a program for generating hyperimmune GBS globulin, we evaluated the safety and immunogenicity of a candidate multivalent GBS vaccine containing purified polysaccharide from types Ia, Ib, II, and III among subjects most likely to develop an immune response following vaccination, i.e. those with pre-existing antibody to GBS. Thirty volunteers prescreened for serum antibody to type III GBS were immunized with a single subcutaneous injection of vaccine containing either 10, 25, or 50 micrograms of each polysaccharide type (Group 1). An additional ten volunteers prescreened for antibody to type Ia were vaccinated with the 50 micrograms dose (Group 2). Vaccination was generally well tolerated with minor reactions occurring in 27% of subjects. Using a quantitative enzyme-linked immunosorbent assay (ELISA), the seroconversion rates (> or = fourfold rise) and geometric mean antibody concentration (GMC in microgram IgG ml-1) 6 weeks after vaccination in Group 1 to type Ia, II, and III were 33% (GMC 5.2), 17% (GMC 3.6), and 70% (GMC 43.4), respectively. Quantitative titers were not available for type Ib, but a fourfold rise in ELISA units was seen in 13% of subjects. In Group 2, seroconversion rates to type Ia and III were 90% (GMC 73.4) and 40% (GMC 22.2), respectively. No significant dose-response effect was detected. Combined analysis of Groups 1 and 2 demonstrated that subjects with prevaccination antibody concentrations > 2 micrograms IgG ml-1 had significantly higher type-specific antibody concentrations following vaccination compared with subjects possessing lower levels of antibody before immunization. We conclude that our tetravalent GBS polysaccharide vaccine is safe but only modestly immunogenic in healthy seropositive adults. More potent vaccines will be required for public health use.

Group B streptococcus and pregnancy

Group B streptococcus is a significant pathogen for both mother and child. routine urine culture in pregnancy will identify and allow treatment of women with asymptomatic bacteriuria. An optimal protocol for the prevention of neonatal sepsis has not yet been developed. While intrapartum antimicrobial prophylaxis appears to provide the best potential, each of the currently suggested protocols has significant drawbacks. Drawbacks include the potential for missing high-risk carriers, failure to treat a significant proportion of those destined to deliver an affected infant because no risk factors are present, and empirical treatment of a large proportion of the population in order to present significant disease in a few. Until an effective program of immunization becomes available, intrapartum prophylaxis of group B streptococcal carriers appears to offer the best hope of reducing the incidence of neonatal disease. Caregivers should adopt a uniform practice with regard to screening and prophylaxis. It is essential that any broad-based screening program include an evaluation of efficacy as well as complications including the development of new etiologic agents as causes of neonatal sepsis and the emergence of resistant bacteria. Further, mothers and newborns should be evaluated for drug adverse reactions and the impact of intrapartum prophylaxis on the use of prolonged empirical broad-spectrum antimicrobial therapy on the asymptomatic infant. Additional research is necessary regarding the required duration of therapy for optimal effect of intrapartum prophylaxis, the need for postnatal prophylaxis of the asymptomatic neonate, and the optimal agent for neonatal prophylaxis (penicillin versus broad-spectrum agents) if neonatal therapy is necessary after intrapartum prophylaxis.

Risk factors for perinatal group B streptococcal disease after amniotic fluid colonization

A group of 1031 parturient women at high risk for intraamniotic infection were studied. Women in whom group B streptococci grew from cultures of the amniotic fluid did not differ in clinical risk factors when compared with similar parturient women without group B streptococcal colonization of amniotic fluid. Patients who had perinatal group B streptococcal disease (maternal or neonatal bacteremia) did not differ from those without disease, by maternal or neonatal acute antibody levels or antibody response, inoculum size, or serotype of the colonizing strain.

Role of circulating complement and polymorphonuclear leukocyte transfusion in treatment and outcome in critically ill neonates with sepsis

We examined the effects of early administration of polymorphonuclear leukocyte (PMN) transfusions in neonates with sepsis by prospectively randomizing 35 consecutive critically ill infants with sepsis, 21 of whom received PMN transfusions in addition to supportive care, one transfusion every 12 hours for a total of five transfusions. Each transfusion consisted of 15 mL/kg containing 0.5 to 1.0 X 10(9) PMN with less than 10% lymphocytes, and was subjected to 1500 rads. PMNs were obtained by continuous-flow centrifugation leukopheresis. Pretreatment values that did not significantly affect survival included weight, gestational age, sex, prematurity, C-reactive protein, initial hematocrit, platelet count and absolute granulocyte count (AGC less than or equal to 1500/mm3), IgM, IgG, IgA, neutrophil supply pool depletion, hypoxia, acidosis, and hypotension. Postnatal age was significantly lower in the nontransfused group than in the transfused group; 2.3 +/- 0.6 vs 6.1 +/- 2.2, (P less than 0.001). Positive blood cultures were obtained in 80% of both groups. Low circulating levels of total hemolytic complement were associated with a poor outcome and higher mortality: 56 +/- 4.0 IU in survivors vs 31 +/- 4.4 IU in nonsurvivors (P less than 0.01). Survival was significantly greater in the PMN transfused group than in the nontransfused group: 20 (95%) of 21 vs nine (64%) of 14 (P less than or equal to 0.05). No untoward effects were attributable to PMN transfusions, either during the study or on subsequent follow-up visits. These preliminary data suggest that early treatment with PMN transfusions improves survival in neonates with overwhelming sepsis. In addition, depleted or low circulating levels of complement may influence prognosis and thus future treatment strategies for neonatal sepsis.

Maternal immunoglobulin allotype (Gm and Km) and neonatal group B streptococcal infection

Gm and Km(1) allotypes in 37 mothers of neonates with severe Group B streptococcal (GBS) infection were compared with 115 mothers of non-infected infants, 36 of whom were known to be colonized with GBS. Deficits in G1m(1) and Km(1), and an increased incidence of G2m(23), were found in mothers of infected infants. Km(1) was associated mainly with the phenotype Gm(1, (2), 3, 17; 23; 5, 10, 11, 21) in mothers of infected infants while being uniformly distributed in mothers of non-infected infants. This study would seem, therefore, to support reports of Gm and Km(1) allotype involvement in maternal response to GBS infection and immunity in the new-born.

Immunotherapy of neonatal septicemia

This chapter has reviewed the deficiencies in immune defense that place the neonate, particularly the premature infant, at increased risk of invasive bacterial disease. We also have reviewed the literature on the rationale for exchange transfusion, granulocyte transfusion, intravenous immunoglobulin, and fibronectin administration as immunotherapeutic agents in infected infants. There have been no randomized controlled trials of exchange transfusion, immunoglobulin, or fibronectin administration in human infants with infection. Granulocyte transfusion in the infected newborn infant has been studied in a controlled fashion, but the results of clinical trials are conflicting. Thus, all of these interventions appear to need further evaluation. We therefore recommend that in the septic newborn infant with neutropenia and an I/T ratio greater than or equal to 0.8, who fails to demonstrate a favorable response to conventional antibacterial chemotherapy and cardiopulmonary support, the administration of approximately 1 X 10(9) irradiated granulocytes per kg may be beneficial. In the absence of equipment to isolate the granulocytes, a double-volume exchange transfusion with fresh heparinized whole blood will provide a similar quantity of functional phagocytes.

Prevalence of type-specific group B streptococcal antibody in human sera: a study of 405 pregnant women

Presence of immunoglobulin G antibody against the five standard serotypes of group B streptococcus was measured by means of indirect immunofluorescence in the sera of 405 women at the time of delivery in the obstetric hospital in Vancouver. Antibody to all five serotypes was present in 22% of women whereas only 9.6% had no detectable antibody to any serotype. Among 47 women with group B streptococcus vaginal colonization, IgG antibody was detected against the homologous colonizing serotype in 100%, 75%, 78%, 89%, and 100% of sera for serotypes Ia, Ib, Ic, II, and III, respectively. This contrasted with the women who had heterologous group B streptococcal vaginal colonization or no colonization in whom 71% had serum IgG antibody to serotype Ia, 36% to Ib, 51% to Ic, 66% to II, and 60% to III. Overall the serum antibody titers were low, and few women had titers greater than 1:20 for any of the five standard serotypes.

Immunoprophylaxis and immunotherapy of neonatal group B streptococcal infections

With emphasis on work from our laboratory, this paper briefly reviews previous studies which have established the basis for immunity to group B streptococcal infections. Quantitative data are presented on the concentration of antibody to the type-specific polysaccharides of group B streptococci in normal adults and infected infants, the protective level in experimental animals, and the influence of prematurity on transplacental passage of antibody. The role of the polymorphonuclear leukocyte in immunity to group B streptococcal infections is critical as supported by in vitro and in vivo experiments as well as clinical observations. Strategies for prevention include antimicrobial chemoprophylaxis and active immunization. Alternative approaches to adjunctive therapy such as administration of specific immune globulin, polymorphonuclear leukocytes, and exchange transfusions are discussed.

Intravenous administration of human IgG to newborn infants: changes in serum antibody levels to group B streptococci

A human IgG preparation was given intravenously to 36 newborn infants admitted to the neonatal intensive care unit because of suspected septicaemia. IgG was given as a single dose of 0.4 g/kg body weight. Patient serum was obtained immediately before and 30 min after terminating the infusion. Blood was also withdrawn 2 days after giving the IgG in eight of the infants. The sera were tested by radioimmunoassay for IgG antibody levels to surface antigens of group B streptococci (GBS) types Ia, Ib, II and III and to R-protein. The mean increases in anti-type Ia, Ib, II, III and R-protein antibodies 30 min after the end of infusion were 81%, 73%, 49%, 60% and 69% of the preinfusion levels, respectively. This was followed by a rapid decrease during the following 2 days to 25%-32% of the initial increases. Based on the above findings, a controlled trial of passive immunisation in the management of neonatal GBS septicaemia seems justified. The rapid decline in antibody levels would necessitate a second infusion 24 h after the initial immunoglobulin administration if the suspicion of septicaemia persists.

Protective levels of human immunoglobulin G antibody to group B streptococcus type Ib

We studied the concentration of circulating human immunoglobulin G (IgG) antibody to the native capsular polysaccharide of group B streptococcus (GBS) type Ib necessary to protect mice against lethal challenge by laboratory and clinical GBS Ib strains. Antibody was measured by an enzyme-linked immunosorbent assay in which native polysaccharide antigen coupled to human serum albumin was used. The assay was standardized by a quantitative precipitation test, using native antigen and specific human IgG antibody purified by affinity chromatography. IgG anti-GBS Ib antibody level-protection curves for 90% lethal dose challenge of mice were sigmoidal. The curves of whole serum and affinity-chromatographed IgG anti-GBS Ib were superimposable. The serum concentrations of human antibody required for complete protection of mice varied with the infecting strain and ranged from 0.038 to 0.175 microgram/ml. Protective levels of human IgG anti-GBS Ib were lower than those we found previously for homologous protection against GBS Ia challenge (range, 0.25 to 1.0 microgram/ml).

Type-specific capsular antigen is associated with virulence in late-onset group B Streptococcal type III disease

Strain differences have been postulated to explain the observation that group B Streptococcus type III (GBS III) late-onset disease occurs in only a fraction of colonized infants. To determine the distribution of type-specific polysaccharide antigen (Ag) in GBS III, Ag was measured by rocket immunoelectrophoresis in both supernatant fluids and EDTA extracts and by radial immunodiffusion in multiple HCl extracts of the pellet from cultures of 10 strains of GBS III. Capsular Ag was defined as the sum of Ag in EDTA extracts + Ag in multiple HCl extracts. Both Ag in EDTA extracts and Ag in supernatant fluids correlated with capsular Ag (r = 0.94). GBS III strains were obtained from the blood of 19 infants with late-onset sepsis, from the cerebrospinal fluid or blood of 22 infants with late-onset meningitis, and from mucosal surfaces of both 18 infants and 12 mothers of infants with low levels of type-specific antibody and asymptomatic colonization. Mean values of Ag in supernatant fluids in strains from infants with late-onset sepsis (1.50 +/- 0.08 micrograms/ml) and late-onset meningitis (1.67 +/- 0.09 micrograms/ml) were significantly greater than those in asymptomatic colonization strains (1.14 +/- 0.05 micrograms/ml; P less than 0.001). The number of organisms required for a 50% lethal dose in the chick embryo, determined in 29 strains, was inversely related to Ag in supernatant fluids (r = -0.60). The demonstration that the quantity of capsular Ag produced by GBS III strains is related to their virulence in chick embryos and to their invasiveness in susceptible infants supports the hypothesis that Ag is a virulence factor in humans.

Immunoprophylaxis and immunotherapy of neonatal group B streptococcal infections

With emphasis on work from our laboratory, this paper briefly reviews previous studies which have established the basis for immunity to group B streptococcal infections. Quantitative data are presented on the concentration of antibody to the type-specific polysaccharides of group B streptococci in normal adults and infected infants, the protective level in experimental animals, and the influence of prematurity on transplacental passage of antibody. The role of the polymorphonuclear leukocyte in immunity to group B streptococcal infections is critical as supported by in vitro and in vivo experiments as well as clinical observations. Strategies for prevention include antimicrobial chemoprophylaxis and active immunization. Alternative approaches to adjunctive therapy such as administration of specific immune globulin, polymorphonuclear leukocytes, and exchange transfusions are discussed.

Immunospecificity and quantitation of an enzyme-linked immunosorbent assay for group B streptococcal antibody

Type-specific antigen was purified from the supernatant of type III group B streptococcal cultures, tyrosylated, and bound to microtiter wells for an enzyme-linked immunosorbent assay. The immunological specificity of the antigen and the assay was shown by (i) reaction only with homologous unabsorbed rabbit sera and (ii) inhibition after incubation of human serum with homologous but not heterologous purified antigen. The assay was quantitated by relating optical density readings to absolute amounts of human immunoglobulin G bound to the microtiter wells.

Association between maternal Gm allotype and neonatal septicaemia with group B streptococci

Thirty-four mothers to infants seriously infected with group B streptococci (GBS) were investigated for G1m (1) and G3m(5) allotype markers. The frequency of Gm (1, -5) was 14.7%, of Gm(1,5) 20.6% and Gm (-1, 5) 64.7%. There was a marked deficit Gm (1) individuals and the distribution significantly differed from that in the normal Swedish populations.

Obstetrical care in future pregnancies after fetal loss in group B streptococcal septicemia. A prevention program based on bacteriological and immunological follow-up

Among 22 mothers of infants infected with group B streptococci (GBS), 19 showed markedly low levels of antibodies against the infecting type. Three of the patients with low antibody levels went through a new pregnancy within 1 yr after they had lost an infant (2 patients) or experienced fetal death due to GBS (1 patient). They were still urogenital carriers of the type of GBS causing the previous infection, and their serum levels of type-specific antibodies remained low. All three went through a successful pregnancy following a prevention program comprising antibiotic treatment from the 28th wk of pregnancy.

Hypersusceptibility of penicillin-treated group B streptococci to bactericidal activity of human polymorphonuclear leukocytes

Pretreatment of serotype Ib group B streptococci with benzylpenicillin, other beta-lactam antibiotics, or vancomycin increased the susceptibility of these bacteria to the bactericidal activity of a mixture of human polymorphonuclear leukocytes and normal human serum. Increased susceptibility of the bacteria to killing by phagocytes was elicited even by exposure to subinhibitory levels of the beta-lactam antibiotics. Inhibitors of protein synthesis did not induce such susceptibility. We investigated the possible biochemical basis of penicillin-induced susceptibility to phagocytosis. Penicillin treatment induced the release of substantial quantities of group B streptococcal surface components into the growth medium (lipoteichoic acid, lipid, and capsular polysaccharide). Labeling of the live streptococci with 3H-labeled penicillin was used to evaluate the effect of exposure to subinhibitory concentrations of this antibiotic on the penicillin-binding proteins. Our results suggested that beta-lactam antibiotics and components of the immune system may act in concert to eliminate invading bacteria.

Antibody response to group B streptococcus type III and AB blood group antigens induced by pneumococcal vaccine

The effect of pneumococcal vaccination on antibodies to Streptococcus pneumoniae type 14, group B streptococcus type III, and AB blood group antigens was studied in 40 vaccinated adults. Fourfold or greater increases in type-specific IgG antibody to Pn-14 were found in 26 of 40 vaccines (mean increase 6.4-fold) and against GBS-III in 16 of the 40 (mean increase 2.9-fold) by an indirect immunofluorescence assay. However, only six of the 26 vaccinees with low levels (titers less than or equal to 20) of GBS-III antibody in prevaccination sera developed titers greater than 20 after vaccination. Thus, vaccination with polyvalent pneumococcal vaccine does not reliably induce high levels of IF antibody to GBS-III. Fourfold or greater increases in IgG isohemagglutinins against blood group A cells were also found in 22 of 27 vaccines (mean increase 4.5-fold) and against blood group B cells in nine of 34 (mean increase 1.7-fold) using the indirect anti-human globulin test. Chromatographic fractionation of selected sera confirmed that the anti-A isohemagglutinins stimulated in group O subjects were of the IgG class. Thus, pneumococcal vaccination during incompatible pregnancy could potentiate AO hemolytic disease of the newborn infant.