Assessment of different methods for detection of group B streptococci carriage among pregnant females

ABSTRACT

Group B streptococci [GBS] cause serious life threatening infections in the newborn. Mortality of GBS sepsis may exceed 50%, and preterm infants are especially at risk. The ability to intervene in the intrapartum transmission of GBS from mother to infant is based on either the recognition of maternal risk factors at the time of delivery or on direct identification of maternal GBS carriers through prenatal screening of cultures obtained at 35 to 37 weeks of gestation. In either case, the institution of appropriate antimicrobial prophylaxis has been shown to reduce the incidence of early onset GBS neonatal sepsis by 69 - 86%. The present study aimed at comparing different methods for detection of GBS colonization. The study also aimed at evaluating urine specimens in comparison to vaginal swabs as effective samples for screening GBS carriage among pregnant females. 134 females at 35-37 weeks of pregnancy were included in the study. Two vaginal swabs and one urine sample were collected from each female. One of the vaginal swabs was directly inoculated onto sheep blood agar and the other swab was immersed into Lim broth to be incubated for 24 hours followed by subculture onto sheep blood agar as well as direct testing for GBS antigen by agglutination. The urine samples on the other hand, were divided into two parts. The first part was cultured on sheep blood agar plates and the second part was inoculated into Lim broth and processed in the same way as the vaginal swabs. GBS was detected in the vaginal swabs and urine specimens of 21 [15.67%] and 11 [7.4%] females respectively. Direct GBS antigen detection in Lim broth was positive in all cases of GBS carriage, whether vaginal or urine. Whereas, only 11 and 19 out of the 21 positive vaginal samples were positive for GBS by direct plating and subculture methods respectively. Direct antigen detection from Lim broth is an effective method for GBS detection. Although urine samples are easier to collect, yet they are not as effective as vaginal swabs in detection of GBS. However, their mere detection raises the question of reporting positive GBS in urine samples of women in the childbearing period, even in insignificant counts, by laboratories when such samples are sent for culture