Transmission of MRSA between mothers and newborns examined

The need to swab the noses of pregnant women and newborns for the presence of MRSA (methicillin-resistant Staphylococcus aureus) may be unfounded, according to a Vanderbilt study now available online and published in the May issue of Pediatrics. The study's senior author, Buddy Creech, M.D., MPH, assistant professor of Pediatrics, said it is often feared that mothers carrying MRSA may risk transmitting an infection to their newborn babies, but Vanderbilt Pediatric Infectious Diseases researchers found that babies rarely became ill from MRSA infections, despite frequently carrying the germ. "Describing the timing and mode of transmission is important, since the most critical finding in this research is that babies are very commonly exposed to MRSA in early infancy, often with strains that aren't likely to cause disease," Creech said. The study enrolled more than 500 pregnant women in Nashville and Memphis. Nasal and vaginal swabs were collected and tested for the presence of bacteria at regular intervals, including at the time of delivery. Babies were swabbed right after birth and at 2 and 4 months of age. Results show little vertical transmission of MRSA from mother to child, Creech said, but babies did closely match their mother's carrier status by 2 months of age. This suggests a mother who carries S. aureus bacteria in her nose will give it to her baby and her baby will become colonized from close contact within six to eight weeks after birth, which is called horizontal transmission. "Labs were finding a substantial amount of MRSA. Even in our study we found 20 percent of pregnant women will have it, as will 20 percent of babies at eight weeks," Creech said. "But there is tremendous anxiety about what that means and, for physicians, what do you do?" "We don't want to overreact to carriage when incidence of disease is low. A lot of babies are colonized. A lot. Twenty percent at 2 months of age is the highest rate we've ever seen, but in our study only two babies got disease," Creech said. Creech says, at this time, the best action when MRSA colonization is detected in a pregnant woman may be no action at all. The next step in research is to determine if mother-to-child transmission of MRSA in infancy might provide benefits, like greater protection against more serious MRSA illnesses later in life.