Community-acquired methicillin resistant Staphylococcus aureus (MRSA) infections are cropping up with surprising frequency in newborn boys, and mom could be involved, researchers reported here.

“Community-acquired methicillin-resistant staph aureus is a substantial and increasing proportion of staph infection in previously healthy neonates,” Regine M. Fortunov, M.D., of Texas Children’s Hospital in Houston. “Individuals who are most at risk are seven to twelve days of age, and male.”

MRSA infections in infants who have not been hospitalized except at birth, and who have had not had surgery other than circumcision, could be due to concurrent infection of mother and child, Dr. Fortunov said at the American Academy of Pediatrics meeting.

She and her colleagues, led by Sheldon L. Kaplan, M.D., had previously detected an unexpected peak in community acquired S. aureus infections in neonates, a finding that prompted them to conduct a retrospective review.

They drew from data on a prospective cohort of all children treated at Texas Children’s hospital for S. aureus infections between the summer of 2001 and the spring of 2005. The cases were classified by route of acquisition, either nosocomial or community acquired.

They looked at the demographics, hospital course and outcome of a subgroup of patients who were younger than 30 days old when they were diagnosed with community-acquired MRSA. The babies, all of whom were full-term or near-term neonates (> 36 weeks gestation) had been healthy before being infected with community acquired S. aureus. They defined as previously healthy any child who had no hospitalizations other than at birth, and no surgery other than circumcision.

They identified a total of 61 cases of MRSA, and 28 cases of methicillin-susceptible S. aureus (MSSA).

“We saw an increase in the total number of infections each year, especially 2004,” Dr. Fortunov said. “This increase was entirely due to an absolute increase in the number of MRSA infections

The proportion of infections caused by methicillin-resistant strains rose from 50% in 2001, to 83% in 2005.

When the authors compared the demographic characteristics of the infants in the MRSA and MSSA groups, they found no differences in mean birth weight, gender, caesarean section rate, hospital days at birth, exposure to antibiotics pre-admission, pets, passive smoking, breast feeding or circumcision.

They also found no significant differences in average time from onset of symptoms to hospital presentation, average white blood cell count, absolute neutrophil count, clindamycin resistance of the isolates or average inpatient stay.

“We did, however, find a significant difference in onset of symptoms,” Dr. Fortunov said. “MRSA infection peaked at seven to 12 days of age, with 51% of infections occurring during this time; we observed no peak in MSSA disease. Additionally, this peak was only observed in male infants.”

Although both MRSA and MSSA occurred predominantly in boys - about 73% in each group - after further analysis the investigators observed an infection peak only in boys infected with MRSA.

In both groups, putulosis in the groin, upper thigh, and sacral area - areas covered by diapers - was a common presentation. Both groups had invasive infections, including shock, musculoskeletal infections, urinary tract infection, perinephric abscess, bacteremia, and empyema. There was one death, in a child with MRSA.

“Interestingly 10 of the 12 invasive infections, including the death, occurred in male infants,” Dr. Fortunov said. She and colleagues had no explanation for this.

Another surprising finding, she said, was that 12 of 89 mothers had a skin infection at the time of the babies’ presentation.

“For some of these mothers, this was their first significant skin infection,” she noted.

The investigators found that the predominant MRSA clone was community USA 300 carrying pvl - a clone known to cause community-acquired disease.

This clone is found in major metropolitan areas throughout the United States, Dr. Fortunov added.

Source: American Academy of Pediatrics