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Dr. Sharon Hillier, Associate Professor at the University of Pittsburgh School
of Medicine, and Director of Reproductive Infectious Disease Research, provides answers
to many of your questions about the bacteria called Group B Streptococcus. In addition,
Dr. Hillier answers questions on bacterial vaginosis, an area of confusion for Group
B Strep carriers. Dr. Hillier is a microbiologist and is on the Group B Strep Association
National Medical Advisory Board.1. Can you explain the similarities and differences between GBS and bacterial vaginosis? What are the symptoms, how is it diagnosed and what is the treatment?
Group B Strep is a microorganism that often lives in the vagina of normal healthy women. About 1 in 5 women carries Group B Strep in the vagina without any problems whatsoever. Bacterial vaginosisis a common type of vaginal infection caused by a group of bacteria acting together. The bacteria that cause bacterial vaginosis include Gardnerella vaginalis, anaerobic bacteria, and genital mycoplasmas. Group B Strep is not a part of the syndrome known as bacterial vaginosis. The symptoms of bacterial vaginosis can include increased malodorous discharge or mild irritation, but half of women may not notice symptoms. Bacterial vaginosis is usually diagnosed in the doctor’s office by looking at the vaginal fluid under the microscope and seeing vaginal cells coated with bacteria called "clue cells". The treatment for bacterial vaginosis is an antibiotic such as metronidazole or clindamycin given vaginally or orally.
2. How does bacterial vaginosis and other bacteria found in the uterus cause preterm labor?
In some women who have bacterial vaginosis who become pregnant, the organisms (the bacteria) found in the vagina move through the cervix and into the placental membranes or the amniotic fluid. When these bacteria invade this normally sterile space, they can cause the mother’s immune system to respond. The result of this immunologic response is that compounds called cytokines are produced which can cause preterm labor to begin. Any micororganism which invades the placental membranes or amniotic fluid can probably cause preterm labor in the same way.
3. Do you think that GBS can cause pre-term labor in the same way that bacterial vaginosis does? Have you found GBS in the uterus?
Yes. Group B Strep can definitely invade the placential membranes. We have found in our studies that women who have GBS in the placental membranes have a much higher likelihood of delivering a preterm low-birth-weight infant. The good news is that placental infection caused by GBS is relatively uncommon. Less than 1% of women delivering at Magee-Womens Hospital have GBS in the placental membranes. (Please note that Magee Womens Hospital routinely screens all patients and treats culture positive women at delivery). One problem is that it is nearly impossible to tell who has developed GBS infections of the placental membranes or amniotic fluid before delivery because these infections are usually asymptomatic. The "first" symptom might be labor.
4. Should a mother who has had preterm labor ask to be screened for bacterial vaginosis?
Yes. If I were pregnant and had a previous preterm infant, I would ask to be screened for bacterial vaginosis. Two different groups of researchers in the United States have demonstrated that treatment of bacterial vaginosis in women with a history of preterm birth can reduce the rate of preterm delivery. Since many women who have bacterial vaginosis may have mild symptoms or may not notice their symptoms it is important for women who may have noticed a mild vaginal odor or increased discharge to talk to their healthcare provider about checking them for bacterial vaginosis.
5. Why has the screening of the pregnant woman for GBS changed from the "old" suggested 26-28 weeks of pregnancy to the new 35-37 weeks of pregnancy?
GBS is an unusual organism in that it can come and go in the vagina of pregnant and non-pregnant women. We call this intermittent colonization. This has made many of the screening strategies for GBS difficult. If you have GBS in your first prenatal visit at 8 or 10 weeks it doesn’t necessarily mean that you’ll have that organism at the time of delivery. Conversely, many women who do not have GBS at the first prenatal visit might have the organism at the time of delivery and not realize they are at risk. Quite a number of studies now have shown that screening for GBS near the time of delivery is the surest way to know reliably whether or not a woman will be colonized with GBS at the time of delivery. Since most women in the U.S. deliver at an average of 35-37 weeks gestation the recommendation for screening has been moved to 35-37 weeks in order that all women have an opportunity to have their screening test done near the time they go into labor. Women who deliver before 37 weeks will be considered preterm and all will be given prophylactic antibiotics (penicillin) during labor to either stop the infection and/or stop the preterm labor and to prevent GBS disease. It is felt that changing the screening time from the second trimester of pregnancy to the third trimester of pregnancy will allow us to more reliably predict which women are colonized with GBS at delivery.
6. New prevention guidelines for GBS have been issued by both the CDC and ACOG with AAP to follow this year. Can you please share your comments on the two strategies from the perspective of a microbiologist. Do you think that hospital labs will prefer one strategy over the other?
I am really thrilled to see these new guidelines being adopted by our public health care policy groups. This has been an area of great confusion for microbiologist who work in clinical laboratories, for healthcare providers, and for women having children. One of the things I really like about the new prevention guidelines is that they specifiy how GBS should be detected in the lab. There are very clear directions for the type of methods which should be used which can help the people working in the laboratory do the best job possible of picking up GBS if it is present. As a microbiologist, I always think it is important to do cultures in order to really determine whether women are at risk for GBS. So, from my viewpoint I prefer the screening for GBS in all women rather than the prevention strategy based on risk factors.
7. What is your role in the NIH/NIAID funded 5 year study entitled, the Group B Strep Initiative (the vaccine research and development headed by Dr. Dennis Kasper)?
For the past three years our group has been evaluating how often GBS can cause infections of the placental membranes. So far we have evaluated over 10,000 placentas from women delivering in Seattle and in Pittsburgh. As part of these studies we have also done vaginal cultures on over 6,000 women. One area that concerns me is the issue that GBS is a cause of preterm delivery. In 1996, Joan Regan, M.D. and her colleagues published a paper showing that women colonized by GBS in the second trimester of pregnancy had a 50% increased risk of having a preterm low-birth-weight infant. In this study the women at risk for having preterm infants were those who had relatively high levels of GBS in their vagina. In our studies, which are ongoing and funded by the GBS Initiative, we have also found that women who have a high density of GBS in the vagina are more likely to have a preterm infant. These studies suggest we need to do further research to evaluate whether treatment of women who carry GBS at high concentrations in the vagina early in pregnancy can be treated to prevent their preterm delivery. This type of approach would be in addition to the strategies which have just been adopted to prevent neonatal sepsis, but would expand the program to include prevention of GBS associated preterm birth.
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