A study on early-onset neonatal group B streptococcal infection, Bulgaria, 2007-2011

This study examines neonatal group B streptococcal (GBS) colonization and its relation to early-onset GBS disease (EOGBSD), based upon the experience of leading obstetrics and gynecology centers in Bulgaria. The objectives of the study were to update neonatal colonization rates and to assess relationships between clinically differentiated cases (culture-proven GBS newborns) and risk factors inherent to the infant and mother, using a computerized file. The neonatal GBS colonization rate ranged from 5.48 to 12.19 per 1000 live births. Maternal-fetal infection (MFI, a provisional clinical diagnosis in culture-proven colonized infants with initial signs of infection that is usually overcome with antibiotic treatment) and/or intrapartum asphyxia (IA) have been demonstrated as the most frequent clinical manifestations, with significant correlations for the primary diagnosis, but not affirmative for the final diagnosis at discharge, resulting from adequate treatment of neonates. MFI and IA were significantly related to prematurity, and reciprocally, prematurity was associated with the risk of MFI, indirectly suggesting that preterm birth or PPROM (preterm premature rupture of membranes, an obstetric indication associated with early labor and delivery, one of the major causes of preterm birth) is a substantial risk factor for EOGBSD. The regression analysis indicated that in the case of a newborn with MFI, a birth weight 593.58 g lower than the birth weight of an infant without this diagnosis might be expected. Testing the inverse relationship, i.e., the way birth weight influences a certain diagnosis (logistic regression) established the presence of a relationship between birth weight categories (degree of prematurity) and the diagnosis of MFI. The proportions and odds ratios, converted into probabilities that a baby would develop MFI, indicate the particularly high risk for newborns with extremely low and very low birth weight: extremely low birth weight (≤1000 g), the probability of developing a MFI is 66%; very low birth weight (1001-1500 g), 81%; low birth weight (the birth weight category including premature and small for gestational age term infants: 1501-2500 g), 40%; normal birth weight (term infants) (>2500 g), 32%. In conclusion, the need to introduce separate categories for early- and late-onset GBS disease in the registration nomenclature of neonatal infectious diseases is highlighted by these results. Drawing up intrapartum antibiotic prophylaxis (IAP) guidelines is also strongly recommended.