“The multistate population-based study conducted during 2003–2004 also identified a greater-than-expected number of cases of early-onset GBS occurring among infants born to women with negative prenatal screening results (61% observed compared with 23%–46% expected cases of early-onset GBS disease among full-term infants) (102).
Some false-negative results are expected because culture is not perfectly sensitive and GBS can be acquired by the mother during the period between screening and delivery. However, the high proportion of cases born to women with negative screening results suggest possible problems in the steps required to identify GBS colonization. Suboptimal specimen collection timing, methods, transport, and/or laboratory processing might be contributing factors.
Among screened women, the date of the antenatal screening test was missing from 36% of labor and delivery charts. Documentation of the date allows for an assessment of whether screening was performed during the recommended gestation time window.”
“Although maternal GBS colonization might increase clinical suspicion for early-onset GBS disease in an infant, in the era of universal screening, >60% of early-onset GBS cases have occurred among infants born to women who had a negative prenatal GBS culture screen (102,203,204). False-negative cases are not unexpected because culture at 35–37 weeks’ gestation will fail to detect some women with intrapartum GBS colonization. As effective prevention strategies are increasingly implemented, a growing proportion of the remaining relatively low burden of disease will reflect inherent limitations in the strategies. Signs of sepsis in any newborn can be an indication of early-onset GBS disease, regardless of maternal colonization status.”
“Because GBS colonization status can change over the course of a pregnancy, the timing of specimen collection for determination of colonization status is important. Because colonization can be transient, colonization early in pregnancy is not predictive of early-onset GBS disease (44). Late third trimester colonization status has been used as a proxy for intrapartum colonization (140). The negative predictive value of GBS cultures performed ≤5 weeks before delivery is 95%–98%; however, the clinical utility decreases when a prenatal culture is performed more than 5 weeks before delivery because the negative predictive value declines (37).”
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