This report characterizes the nosocomial transmission of the CA-MRSA strain MW2 among healthy newborns and, possibly, a postpartum woman. Symptoms developed in 3 patients 2–24 days after hospitalization; 2 may have acquired the bacteria in the hospital or the community. An eighth patient, a mother with catheter-site infection, had an unrelated strain with a pattern suggestive of a hospital-associated strain. The source of the outbreak and mechanism of transmission were not evident, as no cultures of staff members or the environment yielded this particular strain of MRSA. Transmission may have occurred after MW2 was introduced into the hospital by transient colonization of healthcare workers or by contamination of shared medical equipment. The infection control measures enacted in response to the initial cases may have had a role in controlling the outbreak. Widespread screening of healthcare workers for MRSA did not detect the outbreak strain in this and another report (12
). While a potential role for this practice cannot be excluded, current evidence does not support routinely implementing widespread screening for CA-MRSA.
In the pediatric population, risk factors associated with MRSA infections include premature birth or low birth weight, chronic underlying diseases, prolonged hospitalization, invasive or surgical procedures, indwelling catheters, and prolonged use of antimicrobial agents (22
). Outbreaks of S. aureus
have been especially challenging in neonatal nursery units. Prior outbreaks involving the pandemic strain phage type 80/81 were characterized by high colonization rates among infants discharged from nurseries and subsequent transmission to family members (26
). In this report, infection developed in the outpatient setting for 2 patients (following an admission on the involved unit), which suggests carriage of MW2 from the hospital back into the community. Unrecognized CA-MRSA colonization during hospitalization could become an additional method of its dissemination in the community.
Increased prevalence of CA-MRSA has been reported in Chicago, Los Angeles, Texas, and Minnesota (2
). In New York City, CA-MRSA appears less common; 1 investigation reported MRSA carriage in 0.26% of children and their guardians (29
). In our present report, a retrospective analysis of isolates collected from citywide surveillance studies conducted from 1999 to 2003 suggests that ≈1% of all MRSA isolates in Brooklyn are genotypically related to the prototypical North American CA-MRSA, MW2. Since only MRSA isolates that were susceptible to both clindamycin and ciprofloxacin were analyzed, this analysis probably underestimates the true prevalence. Other strains of CA-MRSA (e.g., USA 300) and USA 400 strains that acquired resistance to these antimicrobial agents would have been missed by our screening methods.
The introduction of CA-MRSA strains into neonatal units represents an especially serious challenge. Many of the infections caused by these strains, including some in our report, can be unusually severe and life-threatening (11
). Careful vigilance involving surveillance, identification of these dangerous strains, and implementation of infection control measures, should be helpful in preventing further transmission both within and outside of the hospital.