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BACKGROUND: Current recommendations for reducing the neonatal morbidity and mortality caused by group B streptococcus (GBS) infections support either screening pregnant women at 35 to 37 weeks’ gestation and treating those with positive cultures or treating GBS during labor on the basis of risk factors such as fever or prolonged rupture of membranes. Both of these strategies result in overtreatment (GBS-negative mothers receiving antibiotics) and undertreatment (GBS-positive mothers not receiving antibiotics). A rapid test performed and available at the time of labor may be a useful guide to appropriately treating at-risk mothers, if such a test is sufficiently accurate.
POPULATION STUDIED: A total of 112 pregnant women hospitalized for delivery in Quebec City, Canada, were enrolled. Of these, 57 had intact membranes, and 55 had membranes already ruptured. The authors did not comment on how the women were recruited or enrolled in the study. The prevalence of GBS colonization in this study population was 29.5%, which is similar to the prevalence reported in other community-based studies. The results are therefore likely to be representative of those patients seen by family physicians practicing obstetrics.
STUDY DESIGN AND VALIDITY: Investigators obtained rectal, vaginal, and rectovaginal swabs from the women at the time of admission and again after the rupture of membranes (for those whose membranes were intact on admission). Three tests were performed on each swab at the same laboratory: a standard GBS culture, a conventional polymerase chain reaction (PCR) assay, and a new rapid PCR assay. It was not stated whether those performing the PCR assays were blinded to the culture results.
OUTCOMES MEASURED: PCR assay accuracy was reported in terms of sensitivity, specificity, and predictive values, using the GBS culture as the gold standard.
RESULTS: Using the combined vaginal and anal swab before the rupture of membranes (N=57), each PCR test had a sensitivity and specificity of 100%. For samples obtained after the membranes had ruptured, the sensitivity dropped to only 93.8% for each test (only one false-negative result), while the specificity remained 100%. This corresponds to a positive predictive value of 100% and a negative predictive value of 98.8%. The positive likelihood ratio calculated from this data is 194; the negative likelihood ratio is 0.03. Results were available for the new PCR assay in 45 minutes, for the conventional PCR assay in 100 minutes, and for the GBS culture in 36 hours.
This study shows that PCR assays are highly sensitive and specific in detecting GBS carrier status in pregnant women at the time of delivery and are more rapid than the standard GBS culture. Assuming this test is available in a clinical setting and can be reliably performed, the PCR assay serves as an alternative approach to the management of GBS in pregnancy, especially in hospitals where the screen-and-treat approach is preferred and GBS status is unknown at the time of labor. A rapid test will not suffice in cases of precipitous delivery, which occurred in 15% of the study institution’s deliveries. Implementation studies in other settings are needed to determine if PCR testing is more cost-effective and whether it should replace a clinician’s current approach.
BACKGROUND: Current recommendations for reducing the neonatal morbidity and mortality caused by group B streptococcus (GBS) infections support either screening pregnant women at 35 to 37 weeks’ gestation and treating those with positive cultures or treating GBS during labor on the basis of risk factors such as fever or prolonged rupture of membranes. Both of these strategies result in overtreatment (GBS-negative mothers receiving antibiotics) and undertreatment (GBS-positive mothers not receiving antibiotics). A rapid test performed and available at the time of labor may be a useful guide to appropriately treating at-risk mothers, if such a test is sufficiently accurate.
POPULATION STUDIED: A total of 112 pregnant women hospitalized for delivery in Quebec City, Canada, were enrolled. Of these, 57 had intact membranes, and 55 had membranes already ruptured. The authors did not comment on how the women were recruited or enrolled in the study. The prevalence of GBS colonization in this study population was 29.5%, which is similar to the prevalence reported in other community-based studies. The results are therefore likely to be representative of those patients seen by family physicians practicing obstetrics.
STUDY DESIGN AND VALIDITY: Investigators obtained rectal, vaginal, and rectovaginal swabs from the women at the time of admission and again after the rupture of membranes (for those whose membranes were intact on admission). Three tests were performed on each swab at the same laboratory: a standard GBS culture, a conventional polymerase chain reaction (PCR) assay, and a new rapid PCR assay. It was not stated whether those performing the PCR assays were blinded to the culture results.
OUTCOMES MEASURED: PCR assay accuracy was reported in terms of sensitivity, specificity, and predictive values, using the GBS culture as the gold standard.
RESULTS: Using the combined vaginal and anal swab before the rupture of membranes (N=57), each PCR test had a sensitivity and specificity of 100%. For samples obtained after the membranes had ruptured, the sensitivity dropped to only 93.8% for each test (only one false-negative result), while the specificity remained 100%. This corresponds to a positive predictive value of 100% and a negative predictive value of 98.8%. The positive likelihood ratio calculated from this data is 194; the negative likelihood ratio is 0.03. Results were available for the new PCR assay in 45 minutes, for the conventional PCR assay in 100 minutes, and for the GBS culture in 36 hours.
This study shows that PCR assays are highly sensitive and specific in detecting GBS carrier status in pregnant women at the time of delivery and are more rapid than the standard GBS culture. Assuming this test is available in a clinical setting and can be reliably performed, the PCR assay serves as an alternative approach to the management of GBS in pregnancy, especially in hospitals where the screen-and-treat approach is preferred and GBS status is unknown at the time of labor. A rapid test will not suffice in cases of precipitous delivery, which occurred in 15% of the study institution’s deliveries. Implementation studies in other settings are needed to determine if PCR testing is more cost-effective and whether it should replace a clinician’s current approach.
BACKGROUND: Current recommendations for reducing the neonatal morbidity and mortality caused by group B streptococcus (GBS) infections support either screening pregnant women at 35 to 37 weeks’ gestation and treating those with positive cultures or treating GBS during labor on the basis of risk factors such as fever or prolonged rupture of membranes. Both of these strategies result in overtreatment (GBS-negative mothers receiving antibiotics) and undertreatment (GBS-positive mothers not receiving antibiotics). A rapid test performed and available at the time of labor may be a useful guide to appropriately treating at-risk mothers, if such a test is sufficiently accurate.
POPULATION STUDIED: A total of 112 pregnant women hospitalized for delivery in Quebec City, Canada, were enrolled. Of these, 57 had intact membranes, and 55 had membranes already ruptured. The authors did not comment on how the women were recruited or enrolled in the study. The prevalence of GBS colonization in this study population was 29.5%, which is similar to the prevalence reported in other community-based studies. The results are therefore likely to be representative of those patients seen by family physicians practicing obstetrics.
STUDY DESIGN AND VALIDITY: Investigators obtained rectal, vaginal, and rectovaginal swabs from the women at the time of admission and again after the rupture of membranes (for those whose membranes were intact on admission). Three tests were performed on each swab at the same laboratory: a standard GBS culture, a conventional polymerase chain reaction (PCR) assay, and a new rapid PCR assay. It was not stated whether those performing the PCR assays were blinded to the culture results.
OUTCOMES MEASURED: PCR assay accuracy was reported in terms of sensitivity, specificity, and predictive values, using the GBS culture as the gold standard.
RESULTS: Using the combined vaginal and anal swab before the rupture of membranes (N=57), each PCR test had a sensitivity and specificity of 100%. For samples obtained after the membranes had ruptured, the sensitivity dropped to only 93.8% for each test (only one false-negative result), while the specificity remained 100%. This corresponds to a positive predictive value of 100% and a negative predictive value of 98.8%. The positive likelihood ratio calculated from this data is 194; the negative likelihood ratio is 0.03. Results were available for the new PCR assay in 45 minutes, for the conventional PCR assay in 100 minutes, and for the GBS culture in 36 hours.
This study shows that PCR assays are highly sensitive and specific in detecting GBS carrier status in pregnant women at the time of delivery and are more rapid than the standard GBS culture. Assuming this test is available in a clinical setting and can be reliably performed, the PCR assay serves as an alternative approach to the management of GBS in pregnancy, especially in hospitals where the screen-and-treat approach is preferred and GBS status is unknown at the time of labor. A rapid test will not suffice in cases of precipitous delivery, which occurred in 15% of the study institution’s deliveries. Implementation studies in other settings are needed to determine if PCR testing is more cost-effective and whether it should replace a clinician’s current approach.
The Journal of Family Practice ©2000 Dowden Health Media