ABSTRACT: Group B streptococcus (GBS) is a leading infectious cause of neonatal morbidity and mortality, with maternal GBS colonization a critical risk factor for early-onset disease. Two strategies used to prevent early-onset GBS disease are universal culture-based screening at 35- to 37-week gestation for all pregnant women with intrapartum antibiotic prophylaxis (usually penicillin) given to those with positive results and prophylactic antibiotics provided to all women with obstetric risk factors for GBS transmission, without previous screening. A new commercial real-time polymerase chain reaction (PCR) test for the rapid detection of GBS may accurately reflect intrapartum GBS colonization. This prospective study was designed to compare the intrapartum PCR test with the standard antepartum culture for detecting GBS colonization.
A total of 445 women in labor were enrolled, who had documented antepartum GBS cultures, who did not receive either antepartum or intrapartum antibiotics, and who delivered their infant after the 4-hour threshold of 2 antibiotic doses. On labor and delivery, before the start of antibiotic prophylaxis, a vaginal specimen was collected, using double swabs, 1 swab for each testing method. With the use of intrapartum GBS culture as the criterion standard test, the results of intrapartum PCR tests were compared with the results of antepartum culture to detect GBS colonization. Early-onset GBS sepsis in newborns was diagnosed by clinical signs of infection plus positive blood culture, neonatal C-reactive protein value of greater than 10 mg/L, or chest radiography showing pulmonary infection. Data were analyzed using SPSS version 15. The χ2 test was used for comparisons between groups. P < 0.05 indicated statistical significance.
The 445 women delivered 464 neonates; 12 neonates (2.7%) were admitted to the neonatal intensive care unit owing to GBS sepsis. Mean (SD) gestational age was 39.6 (7.2) weeks. The mean (SD) time for the results of PCR test to be available was 87.8 (12.3) minutes. Group B streptococcus vaginal colonization was detected in 117 women (26.3%) by intrapartum cultures, in 113 (25.4%) by intrapartum PCR tests, and in 73 (16.4%) by antepartum cultures. The sensitivity and specificity of antepartum culture to diagnose GBS colonization were 73% and 95.5%, respectively, compared with 98.3% and 99%, respectively, for the intrapartum PCR test (P > 0.05). The positive and negative predictive values of antepartum cultures to diagnose GBS colonization were 83.9% and 91.6%, respectively, compared with 97.4% and 99.4%, respectively, for the PCR test (P > 0.05). The intrapartum PCR test and antepartum culture had accuracy rates for detecting colonization of 98.8% and 90%, respectively (P > 0.05). The number of neonates admitted to the neonatal intensive care unit was more strongly associated with positive intrapartum cultures and intrapartum PCR tests as compared with positive antepartum cultures (P < 0.05). This can be explained by the antibiotics given to the antepartum-positive mothers, which reduced GBS colonization and sepsis in the neonates.
These results suggest that the intrapartum molecular-based PCR test can be used to screen for GBS colonization. Future trials examining direct costs and outcomes are needed to determine the long-term health benefits of widespread use of the intrapartum PCR test.