Antimicrobial susceptibility and serotype distribution of Streptococcus agalactiae rectovaginal colonising isolates from pregnant women at a tertiary hospital in Pretoria, South Africa: An observational descriptive study.

BACKGROUND: Streptococcus agalactiae or group B streptococcus (GBS) is a significant cause of neonatal sepsis. Intrapartum antibiotic prophylaxis is recommended for pregnant women identified to be rectovaginally colonised between 34 and 37 weeks' gestational age to decrease the risk of invasive disease in their newborns. An effective multivalent GBS vaccine may prevent a broader scope of GBS-associated diseases, such as GBS early-onset disease, GBS late-onset disease, spontaneous abortion, stillbirth and maternal bacteraemia. Serotype distribution of GBS isolates is essential to determine the efficacy of such a vaccine. OBJECTIVES: To investigate serotype distribution and antimicrobial susceptibility patterns of GBS isolates cultured from rectovaginal specimens during pregnancy. METHODS: Sixty-nine archived maternal colonising isolates were tested against penicillin, erythromycin, clindamycin, vancomycin and levofloxacin. Minimum inhibitory concentration testing was performed using the ETEST method. Serotyping was performed by the latex agglutination method. RESULTS: The most common serotypes detected were Ia (54%), III (20%), V (16%), II (6%), IV (2%) and Ib (1%). All isolates were fully susceptible to penicillin, vancomycin and levofloxacin. Eight (11%) and 50 (56%) isolates showed intermediate resistance to erythromycin and clindamycin, respectively, and 1 isolate was resistant to erythromycin. The macrolide-lincosamide-streptogramin B (MLSB) phenomenon was noted in 3 (4%) of the isolates. CONCLUSIONS: GBS-colonising isolates remain susceptible to penicillin, which remains the drug of choice for intrapartum antibiotic prophylaxis and treatment of invasive disease in newborns. Macrolides should only be used if clinically indicated due to the high prevalence of intermediate resistance. A pentavalent GBS vaccine currently in phase I trials should provide coverage for 97% of the isolates identified in this study.

Measles seroprevalence in pregnant women in Soweto, South Africa: a nested cohort study.

OBJECTIVES: Measles infection causes particularly severe disease in young children who, prior to vaccination, are dependent on maternal antibodies for protection against infection. Measles vaccination was introduced into the South African public immunization programme in 1983 and became widely available in 1992. The aim of this study was to determine measles-specific immunoglobulin G (IgG) levels in pregnant women living with and without HIV born before and after measles vaccine introduction in South Africa. METHODS: Measles IgG antibody level from blood obtained at the time of delivery was compared between women who were born before 1983 (n = 349) and since 1992 (n = 349). Serum samples were tested for measles IgG antibody using an enzyme-linked immunosorbent assay. Geometric mean titres (GMTs) and the proportion with seronegative (<200 mIU/mL) or seropositive titres (≥275 mIU/mL) were compared. RESULTS: Women born since 1992 had lower GMTs [379.7 mIU/mL (95% CI 352.7-448.6)] and fewer were seropositive (55.9%, 195/349) than women born before 1983 [905.8 mIU/mL (95% CI 784.7-1045.5); 76.8%, 268/349], for both comparisons p < 0.001. CONCLUSIONS: We found an association between measles vaccine implementation into the public immunization program in South Africa and peri-partum maternal measles immunity, where women born before vaccine introduction had higher measles IgG antibody titres and were more likely to be seropositive. These findings suggest a need to reconsider the infant measles immunization schedule in settings where women have derived immunity mainly from measles vaccine rather than wild-type virus exposure.

Natural acquired humoral immunity against serotype-specific group B Streptococcus rectovaginal colonization acquisition in pregnant women.

Group B Streptococcus (GBS) rectovaginal colonization in pregnant women is associated with invasive GBS disease in newborns, preterm delivery and stillbirths. We studied the association of GBS serotype-specific capsular polysaccharide (CPS) antibody on new acquisition and clearance of rectovaginal GBS colonization in pregnant women from 20 weeks until 37 to 40 weeks' gestation. Serum serotype-specific CPS IgG antibody concentration was measured by multiplex enzyme-linked immunosorbent assay and opsonophagocytic activity (OPA) titres. Rectovaginal swabs were evaluated for GBS colonization, using standard culture methods and serotyping by latex agglutination, at five to six weekly intervals. Higher serotype III CPS antibody concentration was associated with lower risk of rectovaginal acquisition of serotype III during pregnancy (p 0.009). Furthermore, serotype-specific OPA titres to Ia and III were higher in women who remained free of GBS colonization throughout the study compared to those who acquired the homotypic serotype (p <0.001 for both serotypes). Serum CPS IgG values of ≥1µg/mL for serotype V and ≥3µg/mL for serotypes Ia and III were significantly associated with protection against rectovaginal acquisition of the homotypic serotype. A GBS vaccine that induces sufficient capsular antibody in pregnant women, including high OPA titres, could protect against rectovaginal colonization during the latter half of pregnancy.