Sepsis-Causing Bacteria Found in One in Five Mothers

Approximately 20% of women harbor Streptococcus agalactiae (Group B Streptococcus or GBS) in the genital tract, posing a risk of neonatal sepsis – a life-threatening bacterial blood stream infection.

Researchers from the University of Cambridge investigated the presence of GBS in the placenta of pregnant women and discovered an association with the risk of their baby being admitted to a neonatal unit. The study is published in Nature Microbiology.

Why is GBS a concern to neonatal units?

A 2020 study estimated that GBS infection accounted for around 50,000 stillbirths and 100,000 infant deaths. Although the infection can be treated with antibiotics, routine screening for GBS is not common in the UK, causing concern for pregnant women who may not know they are carrying it.

In a previous study, researchers identified GBS in the placenta of ~five percent of women prior to the onset of labor, but the clinical impact of this was not clear. The new study, led by Dr. Francesca Gaccioli, a senior research associate at the Department of Obstetrics and Gynaecology at the University of Cambridge, re-analyzed data from a previous study of 436 infants born at term to explore whether GBS presence in the placenta was associated with neonatal unit admission. The researchers also confirmed their findings in a second cohort of 925 women and their babies.

Detecting GBS in a pregnant mother is not always easy, and, only a small minority of infants exposed to the bacteria were thought to become ill. 

Better detection methods for GBS

The researchers developed an ultrasensitive PCR test, which amplifies tiny amounts of DNA or RNA from a suspected sample to detect GBS.

They found 1 in 200 babies were admitted to the neonatal unit with sepsis associated with GBS – 10 times the previous estimate – yet the clinical assessment of these infants using the current diagnostic testing only identified GBS in less than 1 in 5 of the cases. They also estimated placental GBS was associated with a two to three-fold increased risk of neonatal unit admission.

“We now realize that the clinically detected cases of GBS may represent the tip of the iceberg of complications arising from this infection,” says corresponding author Professor Gordon Smith, head of Obstetrics and Gynaecology at the University of Cambridge.

Gaccioli and colleagues also analyzed serum from the infants’ umbilical cords. Over one third showed increased levels of several cytokines. This observed “cytokine storm” would explain the increased risk of disease, the researcher suggests.

Should we be screening for GBS?

A randomized controlled trial of screening for GBS for treatment with antibiotics is currently underway in the UK. “In the UK, we’ve traditionally not screened mothers for GBS, but our findings – that significantly more newborns are admitted to the neonatal unit as a result of GBS-related sepsis than was previously thought – profoundly changes the risk/benefit balance of universal screening,” says Gaccioli said:

“We hope that the ultra-sensitive test developed by our team might lead to viable point-of-care testing to inform immediate neonatal care,” concludes Smith.

Reference: Gaccioli F, Stephens K, Sovio U, et al. Placental Streptococcus agalactiae DNA is associated with neonatal unit admission and fetal pro-inflammatory cytokines in term infants. Nature Microbiol; 2023. doi: 10.1038/s41564-023-01528-2

This article is a rework of a press release issued by the University of Cambridge. Material has been edited for length and content.