Serotype features of group B Streptococcus vaginal colonization in late pregnant women and their correlation with early -onset neonatal infection / 中华围产医学杂志

ABSTRACT

Objective:To investigate the serotype features of group B Streptococcus (GBS) vaginal colonization in late pregnancies and their relationship with early-onset neonatal GBS disease (GBS-EOD). Methods:Thirty-two strains were isolated from neonates delivered by GBS-positive mothers and hospitalized for GBS-EOD in Xiamen Maternal and Child Care Hospital from June 2016 to June 2018. Another 266 strains were isolated from vaginal samples from randomly selected late pregnant women who received antenatal screening and delivered in the same hospital during the same period with an allocation ratio of 12∶1. A total of 298 strains from mothers and 32 strains from neonates were involved. Every isolate was serotyped with latex agglutination assay. GBS infection caused by eleven serotypes and the correlation between GBS serotypes in late pregnant women and neonatal GBS-EOD were analyzed. Qualitative variables were compared using Chi-square or Fisher's exact test. A correlation analysis was presented by the column contact number C. Multiple analysis of multiple sample rates was performed with Post hoc testing. Differences between groups were analyzed according to the adjusted standardized residual. Results:A total of nine serotypes were identified among the 298 strains isolated from the mothers. The most prevalent serotype wasⅢ [55.0% (164/298)], followed byⅠb [16.4% (49/298)], Ⅰa [11.1% (33/298)], Ⅴ [9.4% (28/298)], Ⅱ [5.0% (15/298)], non-typable [NT, 1.0% (3/298)], and Ⅵ, Ⅷ and Ⅸ [0.7% (2/298) in each]. Neither Ⅳ nor Ⅶ serotype was identified. The 32 strains isolated from neonates with GBS-EOD belonged to five serotypes, which were Ⅲ [18/32 (56.3%)], Ⅰa [8/32 (25.0%)], Ⅰb [3/32 (9.4%)], Ⅱ [2/32 (6.2%)] and Ⅴ [1/32 (3.1%)]. The positive rates of GBS Ⅲ serotype in neonates with pneumonia, sepsis, and meningitis were 6/13, 7/14, and 5/5. However, no statistically significant difference was observed in the distribution of the five serotypes in GBS-EOD neonates ( P=0.654). Thirty neonates (93.7%) were cured, while two (6.3%) died. There were statistically significant differences among neonatal GBS-EOD caused by vertical transmission with Ⅰa, Ⅰb, Ⅱ, Ⅲ and Ⅴ, Ⅵ, Ⅷ, Ⅸ and NT serotypes ( P=0.046, contingency coefficient 0.183). Further analysis showed that the adjusted absolute value of the standardized residual of serotype Ⅰa was 2.7 (>2), and the difference was statistically significant. However, the adjusted absolute value of the standardized residual of serotype Ⅲ was only 0.1, which was not statistically significant. Conclusions:Serotype Ⅲ is the most prevalent GBS serotype in late pregnant women and GBS-EOD neonates, and also the predominant serotype in infants with early-onset meningitis. Serotype Ⅰa could be highly vertically transmitted, while the virulence of serotypes Ⅲ and Ⅰa strains of GBS are the strongest.