Group B streptococci in pregnancy: New perspectives for old challenges.

Abstract

Colonization with group B streptococci during pregnancy has been a long-standing global challenge in maternal-fetal medicine. More than 170 years after Ignaz Semmelweis's seminal observation that handwashing in an obstetric clinic drastically reduced maternal deaths, puerperal sepsis remains a leading cause of maternal morbidity and mortality worldwide.1, 2 In more recent years, group B streptococci (GBS; Streptococcus agalactiae) were isolated from 25% of the obstetric patients with clinically significant bacteremia examined in Ireland 3 and from 15% to 20% of hospitalised women with puerperal bacteremia in the United States.4 GBS is part of the normal intestinal and vaginal flora. It colonises up to 40% of adults5, 6 and between 3% and 41% of the pregnant women worldwide.7-9 GBS carriage in the anorectal or vaginal flora can be intermittent, transient or persistent.10 Conditions during pregnancy allow bacterial multiplication in the vagina, with potential consequences for both the mother and the infant.10 Vaginal colonisation is a risk factor for chorioamnionitis, membrane rupture, preterm labor and stillbirth.11, 12 In immune-compromised populations, including neonates, pregnant women and the elderly people, GBS may become invasive and cause life-threatening conditions such as sepsis, arthritis, pneumonia and meningitis.5 The bacterium was first linked to life-threatening infections in infants under 3 months of age in the 1960s.13 Early-onset disease most often results from the ascending spread of the microorganism into the amniotic fluid, even in the presence of intact membranes.14, 15 The bacterium may also be transmitted from the vagina to infants during delivery.15, 16 GBS is currently the most common aetiological agent of early-onset neonatal sepsis, defined as sepsis that starts within 72 hours or the first week of life,13, 14, 17-19 and is one of the leading causes of morbidity and mortality in preterm and term infants.20 While GBS during pregnancy has historically attracted considerable interest, and advances in antiseptic interventions and antimicrobial therapies improved outcomes, it has been challenging to develop strategies to identify women at high risk for colonisation.10, 21 A better understanding of these risk factors and improved clinical management are ideally positioned to develop targeted efforts to reduce maternal and fetal morbidity and mortality. In the current issue of the IJCP, Chen et al22 had reported a hospital-based cross-sectional survey on pregnant women who were undergoing routine prenatal testing. Obstetric data and bacteriological cultures were available for 2121 participants. The study found a prevalence of 4.9% for vaginal colonisation with GBS, lower than the anogenital colonisation reported in the Caribbean, Europe and North America, and comparable to rates previously found in southern and eastern Asia.7, 23, 24 Women with a BMI over 28 kg/m2 before pregnancy had a significantly higher rate of colonisation as compared to those with a BMI under 28 kg/m2. GBS colonisation increased significantly with gestational age and, for the first time, was higher in participants with a history of lotion use before pregnancy. Interestingly, in a study conducted in Nigeria, pregnant women who reported douching were more likely to be colonised with GBS,26 and previous studies linked douching to disruption of the vaginal flora27 and bacterial vaginosis,28, 29 even though establishing a cause-effect relationship has been challenging.31 A study conducted in Spain between 2013 and 2015 found that performing genital hygiene twice or more daily was associated with a higher risk of GBS colonisation during pregnancy.32 In the study by Chen et al, a history of induced abortions, but not of spontaneous abortions, was associated with significantly lower GBS colonisation rates.22 Previous studies identified various risk factors for GBS colonisation during pregnancy. These include obesity,33 age,34 being African-American33 or Caucasian,35 older age at the first pregnancy,36 a history of GBS during a previous pregnancy,32, 37, 38 being multigravida,34 meconium-stained amniotic fluid, a longer duration of the premature rupture of membranes,39 and smoking.40 The study by Chen et al22 builds on the existing literature and sets the stage for additional, much-needed work to examine the factors associated with GBS colonisation during pregnancy, study causality and interrogate underlying mechanisms. These efforts are powerfully positioned to better understand an important and preventable cause of maternal and infant morbidity and mortality, which has challenged maternal-fetal medicine over centuries and across continents. None.