Geographic Cluster of Community-Acquired Methicillin Resistant Staphylococcus aureus Infections Among Pediatric Patients from Brooklyn, New York

Background: We have recently observed an increase in community-acquired methicillin-resistant Staphylococcus aureus (CA-MRSA) infections among pediatric patients from Brooklyn hospitalized at a university-based teaching hospital in New York City. We performed a prospective study to determine the colonization prevalence of CA-MRSA among hospital admission, genome sequence strains causing infection and identified risk factors associated with CA-MRSA carriage in this population.

Methods:  Colonization data were obtained from routine infection control screening upon admission to the general pediatric and intensive care units.  We used a questionnaire to identify risk factors for MRSA transmission.  Additionally, single patient isolates of CA-MRSA were collected from the clinical microbiology laboratory.  Medical record information was used to ascertain patient infection or colonization and to confirm community onset.  Children from high-risk communities were identified via zip codes.

Preliminary Results: Children from the high risk zip codes were three times as likely to be colonized with MRSA (9% vs 3 % [p=0.04]).  No difference in methicillin-susceptible S. aureus colonization prevalence was observed between children from high-risk and low-risk communities.  Likewise, the MRSA infection rate per 1,000 patient days was 36 for children from high-risk  zip codes, and 3.9 in children from low-risk zip codes (p<0.0001).   All isolates from patients in high risk zip codes analyzed to date belong to genotype USA300, the predominant CA-MRSA clone in the US.  Phylogenetic analyses suggest that these strains arose from expansion of an USA300 CA-MRSA subclone.  Potential risk factors for MRSA infection are being explored in conjunction with public health and community leaders.

Conclusion: We identified a cluster of CA-MRSA strain USA300 among pediatric patients in a high risk Brooklyn community.  Additional genomic comparisons and epidemiological data will be used to inform interventions and interrupt transmission.

Figure 1: Phylogenetic tree of clinical MRSA USA300 isolates from children living in high-risk zip codes (red), Adult and Pediatric patients at NYU Tisch Hospital (Blue) and USA300 Strains from around the USA (Green, provided by Pfizer)