Group B streptococcal carriage in Sweden: a national study on risk factors for mother and infant colonisation

Abstract

Background: To study group B streptococcus (GBS) colonisation in parturients and infants in relation to obstetric outcome and to define serotypes and antibiotic resistance in GBS isolates acquired.

Methods: A population-based, national cohort of parturients and their infants was investigated. During 1 calendar week in 2005 all women giving birth (n=1,754) were requested to participate in the study.

Results: A total of 1,569 mother/infant pairs with obstetric and bacteriological data were obtained. Maternal carriage rate was 25.4% (95% confidence interval (CI): 23.3-27.6). In GBS-positive mothers with vaginal delivery and no intrapartum antibiotics, the infant colonisation rate was 68%. Some 30% of infants were colonised after acute caesarean section, and 0% were colonised after an elective procedure. Duration of transport of maternal recto/vaginal swabs of more than 1 day impeded culture sensitivity. Infant mMales were more frequently colonised than females (76.9 versus 59.8%, odds ratio (OR): 2.16; 95% CI: 1.27-3.70), as were infants born after rupture of membranes > or =24 h (p =0.039). Gestational age, birth weight and duration of labor did not significantly influence infant colonisation. Some 30% of parturients with at least one risk factor for neonatal disease received intrapartum antibiotics. The most common GBS serotypes were type III and V. Some 5% of the isolates were resistant to clindamycin and erythromycin, respectively.

Conclusions: Maternal GBS prevalence and infant transfer rate were high in Sweden. Males were more frequently colonised than females. The sensitivity of maternal cultures decreased with the duration of sample transport. Clindamycin resistance was scarce. The use of intrapartum antibiotics was limited in parturients with obstetric risk factors for early onset group B streptococcal disease.