Testing the Efficacy of a Molecular Surveillance Network: Methicillin-ResistantStaphylococcus aureus(MRSA) and Vancomycin-ResistantEnterococcus faecium(VREF) Genotypes in Six Hospitals in the Metropolitan New York City Area

Abstract

Molecular fingerprinting techniques are rapidly becoming indispensable tools for hospital epidemiology. On the other hand, the relative complexity and unfamiliarity of these techniques to most hospital diagnostic laboratories limit their usefulness. In an attempt to provide a solution for this dilemma, we tested the feasibility and efficacy of a cooperative venture in which molecular typing of isolates recovered from patients in six hospitals was performed at two microbiology research laboratories with expertise in these techniques. In a small preliminary study, 30 methicillin-resistant Staphylococcus aureus (MRSA) and 30 vancomycin-resistant Enterococcus faecium (VREF) isolates were collected over a 3-week period from six hospitals in the metropolitan New York area and transported to the Laboratory of Microbiology at The Rockefeller University during the summer months of 1994. Nineteen of the 27 confirmed MRSA isolates were closely related strains carrying the same mecA and the same Tn554 polymorphs in a pulsed-field gel electrophoresis (PFGE) background represented by closely related subtypes of a single pattern, indicating the wide distribution of this MRSA clone among the participating hospitals. Typing of the same 27 MRSA isolates was also performed at the Tuberculosis Center of the Public Health Research Institute and identical results were obtained. The 29 confirmed VREF isolates were highly heterogeneous and belonged to as many as 23 distinct clonal types as defined by PFGE patterns and probing with vanA. Characterization of the 60 isolates by these methods was completed in one month of full-time effort by a single experienced laboratory assistant guided by a doctoral-level expert in molecular fingerprinting techniques. The collection of samples for both MRSA and VREF was not intended to address epidemiological questions but to determine the feasibility of a multicenter study. On the basis of our preliminary findings we are encouraged that a larger cooperative effort is possible and with the correct sampling method we believe that epidemiological and surveillance studies could be accomplished that would provide a tracking system to assist hospitals, clinics, and chronic care facilities in controlling the spread of multidrug-resistant pathogens.