At-Risk Newborns Don't Need Blood Tests to Screen for Group B Strep

For newborn infants at risk of infection with group B streptococcal (GBS) bacteria, screening blood tests cause extra pain and anxietywithout increasing detection of early-onset GBS disease, reports a study in the October issue of the Pediatric Infectious Disease Journal.

Repeated blood tests to screen at-risk newborns leads to "a negligible clinical yield and a high rate of technical failure," according to the report by Dr. Saar Hashavya and colleagues of Hadassah and Hebrew University Medical Center, Jerusalem.

Group B strep causes potentially life-threatening infections in newborn infants. The infections are often transmitted at birth from mothers who are carriers of the GBS bacteria. Beginning in the 1990s, hospitals started giving preventive antibiotics during the last weeks of pregnancy to mothers carrying GBS. However, sometimes there's not enough time to give the recommended course of treatment before the infant is delivered. In this situation, the infant may undergo blood tests (complete blood count) and blood cultures to detect GBS bacteria.

To evaluate this practice,  Hashavya and coauthors reviewed their medical center's experience with 5,845 GBS-carrier mothers treated from 2005 through 2009. Twenty-eight percent of the mothers were "partially treated," receiving only one dose of antibiotics less than four hours before delivery.

After birth, blood tests and blood cultures were performed in 86 percent of infants born to partially treated mothers. In 18 percent of these infants, a second blood sample was needed because of some abnormal result or technical problems with the first sample.

None of the blood cultures performed within six hours after birth showed the presence of GBS. In a small number of cases (less than 1 percent), the cultures were contaminated with staph bacteria. These infants required intensive clinical observation and repeated blood cultures to confirm that they didn't have GBS infection.

Overall, early-onset GBS infection occurred in 11 out of nearly 54,000 infants. Only two of these infants had mothers who were GBS carriers; neither was identified by blood screening tests. Most of the infants with GBS infection developed symptoms immediately or within the first 12 hours after birthagain, blood tests were not needed to identify the infected patients.

With the introduction of preventive antibiotic treatment, the rate of early-onset GBS infections has greatly decreased. However, there's no clear approach to treatment for infants whose mothers don't receive the full recommended course of treatment before delivery. The new study strongly suggests that blood tests and cultures are not effective or necessary in detecting early-onset GBS in infants born to these partially treated mothers.

Pending further studies, the results support the recently revised recommendation for "expectant management"observing the infant for any sign of illness for at least 48 hoursinstead of blood tests. In infants without symptoms, early blood tests appear to be of little or no value in detecting GBS infection. "More importantly, [the study] shows the drawbacks in terms of unnecessary stress to the newborn and his or her family," Hashavya and coauthors conclude.