To determine the value of prenatal cultures in defining maternal colonization status at delivery, 5,586 pregnant women were screened at prenatal visits for vaginal and rectal carriage of group B streptococci (GBS). GBS were isolated from 1,272 (22.8%). At delivery, semiquantitative cultures were obtained from 393 prenatal carriers, of whom 264 (67.2%) retained carriage at delivery. Seventeen (8.5%) of 200 women with negative prenatal cultures acquired carriage. The predictive value of a positive prenatal culture was highest (72.5%) in women with prenatal vaginal and rectal colonization and lowest (59.7%) in women with only rectal colonization. The predictive value varied inversely with the interval between prenatal sampling and delivery. In mothers with prenatal carriage, density of colonization at parturition was not predicted by the sites of prenatal colonization. Density of colonization, however, strongly influenced rates of vertical transmission to neonates and rates of heavy infant colonization. Ten infants born to prenatally cultured mothers developed group B streptococcal early-onset disease; the mothers of eight (80%) of the 10 had prenatal colonization with the homologous GBS serotype.

The effect of intrapartum ampicillin treatment on vertical transmission of group B streptococci (GBS) was examined in 575 prenatally colonized parturient women and their 580 newborn infants. Eighty women (43 receiving ampicillin) with premature labor and/or prolonged rupture of amniotic membranes were randomized. The other 495 were stratified into groups of 358 (31 receiving ampicillin) with no perinatal risk factors; 119 (28 receiving ampicillin) with premature labor and/or prolonged membrane rupture; and 23 (18 receiving ampicillin) with intrapartum fever. Ampicillin virtually eliminated vertical transmission in the treatment group with no risk factors and in both treatment groups with premature labor and/or prolonged membrane rupture. GBS colonization of neonates was detected only in women with intrapartum fever or brief (less than 1 hr) duration of treatment prior to delivery. Ampicillin treatment was associated with a highly significant reduction in maternal postpartum vaginal colonization by GBS. There were six group B streptococcal early-onset infections in infants of untreated subjects and no cases in treated subjects.

SummaryI'he protective value of pooled human gamma globulin (GG) and a group B streptococcal immune globulin (GBSIG) was studied in a chick embryo and a murine model of group B streptococcal (GBS) infection. Chick embryos were protected by the I V administration of 0.4 to 0.8 mg of GG from three manufacturers against I V challenge with type l a GBS. Two of three G G preparations at doses of 0.4 to 1.65 mg protected chick embryos against type 111, but 1.65 mg of all three preparations failed to protect against GBS types I b and 11. Mice were protected from lethal I P challenges with types l a and I b by the prior IM inoculation of three and two of the three GG preparations at doses of 0.5 to 1.0 mg, respectively. Administration IM of 1 mg of GG failed to protect mice against types 11 and 111.The I V administration of 0.2 mg of GBSIG protected chick embryos against I V inoculation with GBS types la, Ib, 11, and 111. Administration IM of 0.5 mg of GBSIG protected mice against I P challenges with types la, Ib, and 11, but not with type 111. The I P administration of 0.25 mg of GBSlC simultaneously with type 111 GBS protected mice, whereas GG was not protective. GBSIG should undergo clinical trials for the prevention of GBS infections and their recurrences and as a possible adjunct to antibiotic and supportive therapy of severe GBS infections.