Methicillin Resistant Staphylococcus aureus (MRSA) is a nosocomial pathogen often spread patient to patient, and controlled by strict isolation, handwashing, and identification of carriers among patients and caretakers.

During a period of high prevalence of S. aureus infection in the NICU, 5 MRSA isolates were noted among long term patients over about 4 months. MRSA was not controlled by patient isolation and staff education initiated after the first isolate. A better understanding of the epidemiology of this pathogen was needed to help in the control of MRSA in the NICU. Adequate typing of the organisms was essential in this process. Older techniques such as antibiotograms and biotyping have been proven to be of limited efficacy. Chromosomal (DNA) typing is the best, as the genome is the most specific characteristic of any organism. Pulsed field gel electrophoresis(PFGE) was used to type the DNA of the MRSA isolates. PFGE showed all 5 isolates to be distinct, as were most susceptible strains of staph tested. Given this pattern, individual episodes of carriage from outside the unit were suspected, rather than patient to patient spread of an endemic strain. Direct observation of technique by Infection Control personnel confirmed good handwashing and isolation procedures by NICU staff, but poor technique among ancillary staff such as radiology, respiratory, and MD consultants. Several interventions were undertaken to end this outbreak, along with the larger outbreak of susceptible staphylococci. These included education of ancillary staff, handwashing signs at the bedside, and direct confrontation with noncompliant caregivers.

PFGE for DNA typing of organisms is an important tool. In this setting, it rapidly assisted in determining the source of an MRSA nosocomial outbreak, and assisted in the design of effective interventions.