Mothers of infants with neonatal group B streptococcal septicemia are poor responders to bacterial carbohydrate antigens

Group B Streptococcus vaccine development: present status and future considerations, with emphasis on perspectives for low and middle income countries

Globally, group B Streptococcus (GBS) remains the leading cause of sepsis and meningitis in young infants, with its greatest burden in the first 90 days of life. Intrapartum antibiotic prophylaxis (IAP) for women at risk of transmitting GBS to their newborns has been effective in reducing, but not eliminating, the young infant GBS disease burden in many high income countries. However, identification of women at risk and administration of IAP is very difficult in many low and middle income country (LMIC) settings, and is not possible for home deliveries. Immunization of pregnant women with a GBS vaccine represents an alternate pathway to protecting newborns from GBS disease, through the transplacental antibody transfer to the fetus in utero. This approach to prevent GBS disease in young infants is currently under development, and is approaching late stage clinical evaluation. This manuscript includes a review of the natural history of the disease, global disease burden estimates, diagnosis and existing control options in different settings, the biological rationale for a vaccine including previous supportive studies, analysis of current candidates in development, possible correlates of protection and current status of immunogenicity assays. Future potential vaccine development pathways to licensure and use in LMICs, trial design and implementation options are discussed, with the objective to provide a basis for reflection, rather than recommendations.

Naturally occurring antibodies for the group B streptococcal surface immunogenic protein (Sip) in pregnant women and newborn babies

Sip is a surface-exposed protein of GBS, which causes severe neonatal disease. Because Sip elicits a protective immune response in mice, we assessed whether pregnant women and newborns have Sip antibodies. Sera were collected from 644 pregnant women and 176 of their healthy newborns, and 10 newborns with GBS disease and their mothers. Using ELISA, most (99%) women and newborns (97%) had serum Sip antibodies, as did most newborns followed through 6 months. This suggests that naturally occurring Sip antibodies cross the placenta and persist into infancy, which underscores the need to study Sip further as a potential vaccine candidate.

Association between low concentrations of antibodies to protein alpha and Rib and invasive neonatal group B streptococcal infection

BACKGROUND

Infection with group B streptococci (GBS) is a serious neonatal disease. The GBS cell surface proteins alpha and Rib elicit protective immunity in animal models and have been suggested as potential antigens in a vaccine against human GBS disease.

AIMS

To test the hypothesis that transplacentally transferred maternal antibodies to GBS proteins contribute to the protection of the neonate from GBS infection.

METHODS

Thirty neonates with invasive infection were included in a case-control study. IgG antibody concentrations were measured in sera from these neonates, their mothers, and from 60 non-infected controls, neonates as well as mothers.

RESULTS

A clear association was found between concentrations of antibody to proteins alpha and Rib in neonatal and maternal sera, indicating that transplacental transfer had occurred. Moreover, low concentrations of antibodies to alpha and Rib in neonatal sera were associated with invasive GBS infection caused by strains expressing the Rib protein. The odds ratio was 0.0007 (95% confidence interval 0.000 to 0.54) for antibodies to alpha and 0.002 (95% confidence interval 0.000 to 0.57) for antibodies to Rib.

CONCLUSION

These findings support the notion that antibodies to GBS surface proteins contribute to the protection against neonatal infection.

Colonization with Group B streptococci in pregnancy and outcome of infected neonates in Trinidad

BACKGROUND

The present study took place at the antenatal clinics of the San Fernando General Hospital located in the south and the Mount Hope Maternity Hospital located in the north-west of the West Indies, respectively. Participants were from the lower socioeconomic group that included representatives from the two major ethnic groups, East Indians and people of African descent.

METHODS

We prospectively analyzed data on 201 third trimester pregnant women. All had singleton pregnancies. Culture specimens for group B streptococcus (GBS) were obtained from the rectum and anterior one-third of the vagina, and inoculated directly onto selective media. Blood culture from neonates (born to GBS carrier mothers) suspected of sepsis was also screened for GBS. Group B streptococci were identified via colonial morphology, beta-hemolysis, and biochemical reactions, and confirmed via latex agglutination tests. Antimicrobial susceptibility testing was done. Data were computerized and statistically analyzed using the Statistical Package for the Social Sciences. Associations between age, ethnicity and gravidity were evaluated using Pearson's chi2 test.

RESULTS

The prevalence of vaginal and rectal GBS colonization was 32.9%. Group B streptococci were isolated more frequently from women >24 years (36.6%) than those younger than 24 years (26.9%), and more so, from women of East Indian descent (37.3%) than women of African descent (27.2%). Colonization rates were significantly greater among multigravid women than primigravid women (P < 0.001). Of the 13 infants admitted after delivery, five were confirmed cases of sepsis. Group B streptococci were isolated from the blood of three of these infants, and one case was fatal. Although all GBS were fully sensitive to ampicillin and amoxicillin-clavulanic acid, 94% were resistant to tetracycline and approximately 88% to co-trimoxazole. Only approximately 8% were resistant to erythromycin.

CONCLUSION

The carriage rate of GBS among pregnant women in the present and a previous study, remain high. Attempts to establish and implement a program aimed at GBS disease prevention have met with repeated failure. Data on the prevalence of GBS neonatal disease, preventative measures and outcome of infected infants are greatly needed.

Prevention of neonatal group B streptococcal sepsis: is routine antenatal screening appropriate

Four strategies for prevention of early onset neonatal group B streptococcal (GBS) sepsis were considered: A: routine antenatal screening for GBS vaginal carriage at 26-28 weeks' gestation and intrapartum antibiotic prophylaxis for all carriers; B: screening as above and prophylaxis only for carriers with risk factors for sepsis; C: prophylaxis for all women with risk factors; D: as for C plus screening at 37 weeks' gestation and prophylaxis for carriers. The outcomes considered for each option were: the proportion of women given prophylaxis; the risk of anaphylaxis; cases of neonatal GBS sepsis and deaths prevented; costs of screening, prophylaxis and of acute care of remaining cases. Published local and overseas studies of neonatal GBS sepsis, effectiveness of antenatal screening and prophylaxis and estimated costs were evaluated. Any of the proposed strategies can prevent a significant proportion of cases of neonatal GBS sepsis and a strategy for prevention of neonatal group B streptococcal sepsis should be part of routine obstetric practice. Strategy C is simple, effective, inexpensive and avoids unnecessary antibiotic use; it is recommended particularly when antenatal care is provided mainly in community or private practice. Strategy A (using vaginal and rectal swabs for screening) could prevent more cases, but at greater cost which could be justified only if protocols can be properly implemented and monitored.

Prevalence of group B streptococcal colonization in pregnant third trimester women in Trinidad

A study of colonization by group B streptococcus was conducted in 204 pregnant women in their third trimester. Positive cultures were obtained from vaginal and rectal swabs in 64 (31.4%) of these women. No significant differences in colonization rates were noted on the basis of ethnicity (race) and gravidity. However, there was a significant difference in the rate of colonization of vagina and rectum. Fifty-two (25.5%) women had positive isolates from vaginal swabs compared with 26 (12.7%) women with positive rectal isolates (P < 0.05). There was a significant trend of increasing prevalence with increasing age. Colonization was not significantly greater in multigravid than in primigravid women. There was no significant difference between colonization in Negro (black) women and colonization in East Indian women.

Prevention of excess neonatal morbidity associated with group B streptococci by vaginal chlorhexidine disinfection during labour. The Swedish Chlorhexidine Study Group

Streptococcus agalactiae transmitted to infants from the vagina during birth is an important cause of invasive neonatal infection. We have done a prospective, randomised, double-blind, placebo-controlled, multi-centre study of chlorhexidine prophylaxis to prevent neonatal disease due to vaginal transmission of S agalactiae. On arrival in the delivery room, swabs were taken for culture from the vaginas of 4483 women who were expecting a full-term single birth. Vaginal flushing was then done with either 60 ml chlorhexidine diacetate (2 g/l) (2238 women) or saline placebo (2245) and this procedure was repeated every 6 h until delivery. The rate of admission of babies to special-care neonatal units within 48 h of delivery was the primary end point. For babies born to placebo-treated women, maternal carriage of S agalactiae was associated with a significant increase in the rate of admission compared with non-colonised mothers (5.4 vs 2.4%; RR 2.31, 95% CI 1.39-3.86; p = 0.002). Chlorhexidine reduced the admission rate for infants born of carrier mothers to 2.8% (RR 1.95, 95% CI 0.94-4.03), and for infants born to all mothers to 2.0% (RR 1.48, 95% CI 1.01-2.16; p = 0.04). Maternal S agalactiae colonisation is associated with excess early neonatal morbidity, apparently related to aspiration of the organism, that can be reduced with chlorhexidine disinfection of the vagina during labour.

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.

Protective activity of Vi capsular polysaccharide vaccine against typhoid fever

The protective efficacy against typhoid fever of a single intramuscular injection of 25 micrograms of the Vi capsular polysaccharide (CPS) was assessed in a randomised double-blind controlled trial. Vaccination of 11,384 children was followed by 21 months' surveillance. 47 blood-culture-proven cases of typhoid occurred in children who received meningococcal A + C CPS vaccine and 19 cases in those vaccinated with Vi CPS. Protective efficacy was 60% calculated from the day of vaccination and 64% from 6 weeks after vaccination. Surveillance also included 11,691 unvaccinated children; 173 cases occurred in this group. Protective efficacy in relation to the unvaccinated group was 77.4% and 81.0% after 21 months, calculated immediately and 6 weeks after vaccination, respectively. Vaccination was associated with minimum local side-effects, and an increase in anti-Vi antibodies occurred, as measured by radioimmunoassay and enzyme-linked immunosorbent assay. Antibody levels remained significantly raised at 6 and 12 months post vaccination. Vi CPS is thus a safe and effective means of typhoid vaccination.

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.