Dr Mayra Bermudez Martinez: Group B Streptococcus (GBS) is one of the most common causes of severe neonatal infections. Early-onset GBS disease (GBS EOD) occurs during the first seven days after delivery; the majority of cases present in the first 24 hours of life, with symptoms of respiratory disease, sepsis and meningitis. Late-onset GBS disease (GBS LOD) develops after seven days to the third month of life.
Mortality of GBS EOD is about 10-30%, with the highest risk in preterm neonates. The most important factor predicting GBS EOD in neonates is GBS contact during vaginal delivery. The maternal colonisation rate is 10-30% in most European countries, and the transmission rate to newborns during delivery is 40-60%. Of those, 1-2% of term infants and 8% of preterm infants develop GBS EOD.
It is important to know that the GBS colonisation of the maternal genital tract can be transient, persistent or intermittent during pregnancy and most of the women colonised with GBS are asymptomatic. A timely and accurate identification of mothers with GBS colonisation at delivery is required, so that intrapartum antibiotics prophylaxis (IAP) can be administrated appropriately to reduce the risk of GBS transmission and related GBS EOD of the neonate.
The closer to delivery a bacteriological screening is performed, the greater its utility. However, on-site testing directly before delivery cannot be achieved by culture-based analysis, due to prolonged turnaround time, which is 24-48 hours. Now, a universal intrapartum screening using a fast and sensitive real-time PCR test can be achieved, identifying GBS-colonised women at the time of delivery, which is crucial for implementation of IAP.
Implementing IAP for GBS-colonised mothers can prevent more than 80% of GBS EOD. Beta-lactam antibiotics such as penicillin G, ampicillin and cefazolin remain the first-line drugs of choice for intrapartum prophylaxis. Penicillin-allergic women at high risk of anaphylaxis should receive alternative drugs such as clindamycin or vancomycin following antibiotic resistance testing. IAP should be initiated at least four hours before labour, to prevent mother-to-newborn transmission. Antepartum antibiotic prophylaxis several days before delivery is not recommended.
Until now, the strategies for prevention of GBS EOD were different between European countries. They included a riskbased strategy offering IAP to all women with recognised risk factors during labour; a screening strategy based on antenatal GBS culture analysis during the last trimester of pregnancy, generally between 35-37 weeks of gestation, and combinations of these two strategies. In 2013, the European consensus conference recommended a new strategy for IAP based on universal intrapartum GBS screening using a pointof- care nucleic acid amplification test (POCT).
A screening-based strategy with a universal intrapartum GBS screening using POCT real-time PCR allows exact identification of GBS-colonised women during labour and subsequent implementation of appropriate IAP. Antenatal culture-based testing several weeks before delivery can detect the majority of GBS-colonised patients; however, colonisation status varies throughout pregnancy, resulting in under and overestimation of GBS-colonised women at delivery. Always, a risk-based strategy for IAP is recommended; however, a risk-based strategy alone will miss approximately 40-60% of GBS-colonised patients.
Universal intrapartum GBS screening by POCT PCR is the base for sensitive identification of colonised women directly before delivery. Focusing on GBS-colonised women directly before labour can avoid under and overdiagnosis of GBS colonisation at the critical delivery time.