If it's the same as my other two pregnancies, they take a long cotton swap and swap around your genitals and rectum
They just swab you andnud its positive they will give antibotics threw iv for baby xx it can make you ill and its life threatening to newborns but it doesnt effect or harm everyone with my first it broke my waters early at 12weeks but I didnt have my daugther unt 23weeks but dont worry you will be fine