To determine the efficacy of mupirocin ointment in reducing nasal colonization with mupirocin-susceptible, methicillin-resistant Staphylococcus aureus (MS MRSA) as well as mupirocin-resistant MRSA (MR MRSA).

Prospective evaluation in which patients colonized with MRSA were treated twice daily with 2% topical mupirocin ointment for 5 days.

James H. Quillen Veterans' Affairs Medical Center.

Forty hospitalized patients with two anterior nares cultures positive for MRSA within a 7-day period.

Treated patients had post-treatment cultures at day 3 and weeks 1,2, and 4. Isolates underwent mupirocin-susceptibility testing and DNA typing. MRSA clearance and type turnover were assessed for isolates that were mupirocin-susceptible, low-level (LL) MR MRSA and high-level (HL) MR MRSA.

Post-treatment nares cultures on day 3 were negative for 78.5%, 80%, and 27.7% of patients with MS MRSA, LL-MR MRSA, and HL-MR MRSA, respectively. Sustained culture negativity at 1 to 4 weeks was more common in the MS MRSA group (91%) than in the LL-MR MRSA group (25%) or the HL-MR MRSA group (25%). Positive post-treatment cultures usually showed the same DNA pattern relative to baseline. Plasmid curing of 18 HL-MR MRSA resulted in 15 MS MRSA and 3 LL-MR MRSA.

Mupirocin was effective in eradicating MS MRSA, but strains of MR MRSA often persisted after treatment. This appeared to reflect treatment failure rather than exogenous recolonization. MR MRSA is now more prevalent and it is appropriate to sample MRSA populations for mupirocin susceptibility prior to incorporating mupirocin into infection control programs.

To describe the clinical and molecular epidemiology of mupirocin-resistant (MR) and mupirocin-susceptible (MS) methicillin-resistant Staphylococcus aureus (MRSA) at a Veterans' Affairs hospital and to assess risk factors associated with the acquisition of MR MRSA.

All clinical MRSA isolates for the period October 1990 through March 1995 underwent susceptibility testing to mupirocin. Mupirocin resistance trends were measured, and MS MRSA and MR MRSA isolates underwent typing by pulsed-field gel electrophoresis (PFGE). A retrospective case-control study was conducted to evaluate risk factors for having MR versus MS MRSA.

The James H. Quillen Veterans' Affairs Medical Center in Mountain Home, Tennessee, included a 324-bed acute-care hospital, a 120-bed nursing home, and a 525-bed domiciliary. Colonizations and infections with MRSA were endemic, and mupirocin ointment was commonly used.

Inpatients and outpatients at the facility.

MS MRSA was recovered from 506 patients and MR MRSA from 126. Among MR MRSA isolates, 58% showed low-level mupirocin resistance (minimum inhibitory concentration [MIC] ≥4 to 256 μg/mL), and 42% showed high-level mupirocin resistance (MIC ≥512 μg/mL). A significant increase (P=.002) in the number of high-level MR isolates occurred during the 1993 to 1995 period. A case-control study showed that presence of a decubitus ulcer correlated with high-level resistant isolates (P<.05). The distribution of PFGE patterns did not differ for MR and MS MRSA.

Use of mupirocin ointment in a program aimed at managing endemic MRSA infection or colonization resulted in a significant increase in the recovery of high-level MR MRSA isolates. These isolates appeared to emerge from our existing MRSA pool. A case-control study provided few clues concerning patients likely to harbor MR MRSA We confirmed the position that the extended use of mupirocin ointment should be avoided in settings where MRSA is endemic.