When interviewing parents who are about to have a baby I am frequently asked "What is Group B strep infection? My obstetrician said I would be tested for it and possibly treated." 

For the last 10 years it has become customary to test -- and treat mothers who are positive -- for Group B infection, which can be a serious infection in newborns if not treated. 

Dr. Robert Lenfestey, an expert in neonatology, describes this condition and its treatment.

Robert W. Lenfestey, MDBefore women and babies were routinely tested and treated for Group B streptococcus (GBS) infection, as many as 50 percent of babies with GBS died from the infection. Since that time deaths from GBS infection have fallen dramatically.

Pregnant women are usually tested for GBS by their obstetrician between 35 and 37 weeks of pregnancy. To test for GBS, a urine test and a swab of the vagina and rectum are sent to see if GBS is present.

If GBS is found, then antibiotics will be given at the time of labor. Additionally, a pregnant woman who previously gave birth to an infant with GBS infection will also receive antibiotics during pregnancy.

Occasionally, pregnant women in labor do not know if they have GBS. This may be because they are in premature labor before 35-37 weeks of pregnancy and have not been tested yet, or because they did not receive the test for GBS during their pregnancy. In this case, a woman will be given antibiotics during labor if she is delivering at less than 37 weeks of pregnancy, or if she has a fever more than 100.4^ºF, or her water has been broken for more than 18 hours.

Penicillin or ampicillin are the most effective antibiotics against Group B strep. To be considered effective, the antibiotic must be given more than four hours before delivery.

In rare cases, women are allergic to penicillin and ampicillin. In these cases clindamycin is given; however, clindamycin is not as effective as penicillin or ampicillin at preventing GBS infection in babies.

Diagnosing GBS in Babies

Once the baby is born, he or she will be evaluated by the doctor to see if the baby has any sign of an infection.

If the mother has been diagnosed with an infection of the uterus or if the baby has any signs of infection then the baby will have a blood test for infection sent and will be started on antibiotics. In addition to the blood test, a spinal tap to test the fluid around the baby's brain and spinal cord may be done.

If the baby was born at less than 35 weeks of pregnancy or if the antibiotics were given less than four hours before delivery or if another antibiotic besides penicillin or ampicillin was used, then the baby is still at risk for GBS infection and will have a blood test for infection performed.

However, the baby does not need to be started on antibiotics or have additional tests performed unless the blood test or the baby shows signs of infection.

If the baby is born after 35 weeks of pregnancy and the mother received penicillin or ampicillin greater than four hours before delivery, then no testing or antibiotic treatment are needed for the baby.

GBS Take Home Points

The mother should get antibiotics at delivery if:

• Tests for GBS are positive in the mother or
• The mother has a risk factor or
• The mother had a baby with GBS infection previously

The baby requires no treatment if:

• The mother does not have GBS or
• The mother was treated with penicillin for more than four hours before delivery

The baby should get blood tests for infection if:

• The mother is diagnosed with an infection called chorioamnionitis or
• The mother has GBS and was not treated with Penicillin for more than four hours before delivery

The baby should get blood tests for infection and antibiotics if:

• The baby has signs of infection on examination by the doctor or
• Blood tests indicate that the baby has an infection

-- Robert Lenfestey, MD, is a Duke neonatologist with a research focus in infectious disease and quality improvement.