June 18, 2009
False Negatives Found In Maternal Test Leaves Babies Untreated
In a huge effort to test pregnant women for deadly bacteria that can be transmitted to their babies, it was found that many test results were false, leaving some infants untreated.
A study found that the test missed more of the infections than usually expected. The mothers that tested positive for the Group B strep bacteria were given antibiotics during labor to decrease the chance of passing it to their infants.Group B Strep is a species of the normal flora of the female urogenital tract and rectum and can be transferred to a newborn as it passes through the birth canal. Though harmless to most adults in the western world, it is a major cause of an invasion of bacteria into the bloodstream of the newborn, which can lead to blood infections, pneumonia, meningitis, mental retardation or hearing and vision loss, and death.
Occurring in less than 1 in every 3,000 births, it is not a common problem. However, the terrible implications of the infection drove the Centers for Disease Control and Prevention (CDC) and doctor groups to recommend routine tests of all pregnant women in 2002.
Led by the CDC, it is the first large national study of the screening program. The CDC intends to do follow-up research to find the cause of the false negative results.
Experts say it is possible that there were problems with the collection of samples for the accuracy of the standard lab test used to screen for the germ. It is also possible that the mother was not infected until after the test.
"There are a lot of unknowns here," said deputy medical director for the March of Dimes Dr. Diane Ashton.
No one considers the screening program to be a failure by any means. The study found that screenings almost doubled in only a few years, and infant infections from Group B strep that were already decreasing due to earlier prevention efforts dropped another 27%.
According to Dr. Barbara Stoll, pediatrics chairman at Emory University medical school, "The guidelines have been an unabashed success."
The study is based on a database that keeps track of Group B strep disease cases in 10 states. Within two years, 250 infants out of nearly 7,700 got the infection at birth. The results were compared to a similar study conducted in the late 1990s, before the screening recommendations were in place.
The positive side of all of this is that the screening rate got a boost from 48% to 85% of pregnant women. And the antibiotics appear to be very effective, according to co-author Stephanie Schrag of CDC.
But Schrag and others still admit that the amount of false negatives were still disappointing as well as unexpected.
Previous studies led the researchers to calculate cases if false negatives involving full-term infants to be between 44 to 86, but the final analysis was 116 cases, or about 60% of infected full-term infants in the study were born to mothers who had mistakenly been tested negative for the infection.
The rest of the infected full-term babies had either not been screened or were born to mothers who tested positive.
Since timing may be a possible issue, it is recommended that doctors test mothers for the bacteria at 35 to 37 weeks of pregnancy by doing a vaginal and rectal swab. Group B strep infections can come on quickly, however, and some tests might have been done before the bacteria appeared.
The study's authors suggest quicker tests could make a difference, and it may be an even better solution to create a new vaccine against Group B strep.
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