Group B streptococcus, known as group B strep, is one of many kinds of streptococcus bacteria that infect humans. Although group B strep can live in a healthy person's body without causing illness, 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. Pregnant women get tested for group B strep during pregnancy. To prevent newborn infection, any women with group B strep infection are treated in the last weeks of pregnancy or during labor.