Infant S. aureus colonization rises after birth in cases of maternal nasal carriage.(Obstetrics)

Washington -- Staphylococcus aureus colonization increases significantly in the first 2 months of life and appears to be positively associated with maternal carriage, based on a study of 200 mother-neonate pairs.

At delivery, S. aureus detection among 165 infants was 8%; at discharge, detection among 190 infants was 7%. However, at age 2 months, 33% of infants were colonized with S. aureus--17% with methicillin-resistant S. aureus (MRSA), Dr. Clarence B. (Buddy) Creech II said at the jointly held annual Interscience Conference on Antimicrobial Agents and Chemotherapy and the annual meeting of the Infectious Diseases Society of America.

"In those mothers who had no evidence of nasal colonization at 2 months, the vast majority of their infants also remained uncolonized. However, among those mothers who had methiallin-susceptible S. aureus (MSSA) nasal colonization [at 2 months], 51 % of their infants were nasally colonized with MSSA." Of mothers with MRSA nasal colonization, 45% of their infants had nasal MRSA colonization at 2 months.

"We were able to detect MRSA carriage in a significant number of mothers and infants; however, we have not observed many infections in this cohort," Dr. Creech said in an interview. The findings demonstrate that staphylococci are commensal organisms and part of normal flora. "The question that remains is whether certain strains of staphylococci, in certain hosts, are more likely to cause disease than others."

Pregnant women were recruited at the time of group B streptococcus (GBS) screening between gestational weeks 35 and 37. At that time, nasal swabs for S. aureus and rectovaginal swabs for GBS and S. aureus were taken. Nasal swabs were repeated in the mother on the day of delivery and at 2 months post partum. Neonatal nasal and umbilical swabs were obtained within 2 hours of birth and nasal swabs were repeated on the day of discharge and at 2 months.

At the time of the presentation, 431 pregnant women had been enrolled. Dr. Creech, of the pediatric infectious diseases department at Van-derbilt University, Nashville, Term., presented ...