Are active microbiological surveillance and subsequent isolation needed to prevent the spread of methicillin-resistant Staphylococcus aureus?

BACKGROUND

Infection-control strategies usually combine several interventions. The relative value of individual interventions, however, is rarely determined. We assessed the effect of daily microbiological surveillance alone (e.g., without report of culture results or isolating colonized patients) as an infection-control measure on the spread of methicillin-susceptible Staphylococcus aureus (MSSA) and methicillin-resistant S. aureus (MRSA) in a medical intensive care unit (MICU).

METHODS

Colonization of patients with MSSA and MRSA was assessed by cultures of nasal swabs obtained daily and, if a patient was intubated, by cultures of additional endotracheal aspirates. Pulsed-field gel electrophoresis was used to determine relatedness between MSSA or MRSA isolates in surveillance cultures (i.e., cultures of nasal swab specimens obtained daily) and those in clinical cultures (i.e., any other culture performed for clinical purposes). Adherence to infection-control measures by health care workers (HCWs) was determined by observations of HCW-patient interaction.

RESULTS

During a 10-week period, surveillance cultures were performed for 158 patients. Fifty-five patients (34.8%) were colonized with MSSA, and 9 (5.7%) were colonized with MRSA. Sixty-two patients were colonized before admission to the hospital (53 had MSSA, and 9 had MRSA). Two patients appeared to have acquired MSSA in the MICU, but, on the basis of genotyping analysis, we determined that this was not the result of cross-acquisition.

CONCLUSION

Surveillance cultures and genotyping of MRSA and MSSA isolates demonstrated the absence of cross-transmission among patients in the MICU, despite ongoing introduction of these pathogens. Reporting culture results and isolating colonized patients, as suggested by some guidelines, would have falsely suggested the success of such infection-control policies.