Group B streptococcus, known as group B strep, is one of many kinds of streptococcus bacteria that infect humans. Group B strep can live in a healthy person's body without causing illness. But it can be life-threatening.

People who are at risk for severe group B strep infection include newborns who catch it from their mothers during childbirth and people who have weakened immune systems (as from chronic illness or cancer treatment).

Group B strep is treated with antibiotics. Testing for group B strep is done during pregnancy. To prevent newborn infection, anyone with group B strep infection is treated in the last weeks of pregnancy or during labour.