A clonal outbreak of rifampicin-resistant methicillin-resistant Staphylococcus aureus (MRSA) in an intensive care unit

We investigated an outbreak of a rifampicin-resistant methicillin-resistant Staphylococcus aureus (MRSA) strain which occurred in our intensive care unit (ICU). Prospective laboratory-based surveillance on all clinical isolates of MRSA and routine screening of patients to detect MRSA colonisation are both performed on ICU patients.

Prior to 2004, less than 1.5% of clinical MRSA isolates from our entire healthcare network were rifampicin-resistant. However, between July and September 2004, seven patients with rifampicin-resistant MRSA were identified in the ICU after a mean length of stay of 18 days. Isolates from six of the seven patients were typed by pulsed-field gel electrophoresis (PFGE), and were identical.

All screening and clinical MRSA isolates from the ICU since this cluster have displayed susceptibility to rifampicin. Resistance to rifampicin may occur via single-step resistance during rifampicin monotherapy or possibly with the use of venous catheters impregnated with rifampicin, although this was not the case in this outbreak. This outbreak of rifampicin-resistant MRSA is an indication of the emerging problem that multidrug-resistant S. aureus pose, and reminds both clinicians and infection control staff to be vigilant in identifying these outbreaks and preventing their spread.