Newborns of S. aureus carrier mothers were likely to acquire infection

51st ICAAC

CHICAGO — More than 40% of mothers who carried Staphylococcus aureus infection had newborns who acquired the infection, according to findings presented at the 51st Interscience Conference on Antimicrobial Agents and Chemotherapy held here.

The aim of the prospective longitudinal cohort study of mothers and their newborns study was twofold: to determine the risks of newborns to acquire S. aureus infection, and to assess the natural history of S. aureus carriage during the first year of life.

Gili Regev-Yochay, MD, of Sheba Medical Center in Ramat Gan, Israel, told Infectious Diseases in Children that mothers were recruited late in pregnancy: “We then followed the mothers and infants for a year every month.”

“What we see is that the mothers who are carriers transmit highly to their children,” Regev-Yochay said. “Within the first 3 days of life, 30% of carriers had transmitted the infection to their children. However, we saw that transmission did not occur immediately during birth, but within the first 24 hours or first 3 days. Very obviously the strain is from the mother. However, transmission was probably horizontal and not vertical through the birth canal.”

Regev-Yochay said that the main predictor for children developing S. aureus infection is if the mother is a carrier.

Mothers who were carriers were divided by whether they were persistent or transient carriers. “Children born to persistent carriers were higher carriers than the children of transient carriers,” Regev-Yochay said. “But even the children born to persistent carriers tend to acquire [S. aureus] at the age of 1 month and then gradually lose it.”

In stage 1 of the study, newborns exposed to mothers who were carriers of S. aureus were compared with newborns of non-carrier mothers. In stage 2, newborns of carrier mothers were followed for 1 year.

Carrier status of mothers was determined via nose and vaginal screening during pregnancy and after labor, according to Regev-Yochay. Nasal, umbilical and rectal swabs were used to determine whether the newborns were infected. These swabs were conducted immediately after delivery and at discharge.

Mothers in the carrier group were screened monthly by nasal swab; newborns in this group were screened monthly by rectal swab.

The researchers collected demographic and medical data in addition to performing antibiotic susceptibility testing and PFGE.

There were 216 mother-newborn pairs included in stage 1. Forty-two percent of newborns from carrier mothers acquired S. aureus infection, compared with 7.4% of newborns from non-carrier mothers (RR=6.1; adjusted RR=5.6).

Among infants of carrier mothers, 81% acquired the same S. aureus strain as the mother, 6% acquired only a different strain from the mother and 12% remained persistent non-carriers of the infection. –

Children of persistent carrier mothers acquired S. aureus infection 92% of the time, compared with a 67% acquisition rate among children of transient carrier mothers (P=.09).

Among the children who acquired S. aureus infection, 79% acquired it at 1 month, 50% carried it persistently for 7 to 12 months and 50% carried it for 3 to 6 months.

Follow-up results yielded no methicillin-resistant Staphylococcus aureus infections. - by Rob Volansky

Disclosure:The researchers reported no financial disclosures.

For more information:

Regev-Yochay G. #G3-178. The Dynamics of Staphylococcus aureus Colonization During the First Year of Life. Presented at: 51st ICAAC. Sept. 17-20, 2011. Chicago.

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