Resistance to methicillin and virulence of Staphylococcus aureus strains in bacteriemic cancer patients.

OBJECTIVE: To estimate the relation between resistance to methicillin and virulence in strains of Staph. aureus by estimating the survival at day 30.

DESIGN: Case control analysis.

SETTING: Inpatients at a major Cancer Referral Center.

PATIENTS: 21 patients with methicillin-resistant Staph. aureus (MRSA) bactaeremia and 45 patients with methicillin-susceptible Staph. aureus (MSSA) bactaeremia, all treated with vancomycin.

MEASUREMENTS AND MAIN RESULTS: Fewer MRSA than MSSA patients were neutropenic (p = 0.04), but more MRSA patients were hospitalized in intensive care units (p = 0.03), had had surgical episodes (p = 0.06). MRSA patients also had more microbiological samples cultured (p = 0.007). The outcome of the bacteriemic episodes in 14 MRSA and 14 MSSA patients matched for these four factors showed that blood cultures from MRSA patients remained positive significantly longer (p = 0.04), but that survival and length of hospital stay were not significantly different.

CONCLUSIONS: These results do not indicate that methicillin-resistance in Staph. aureus is associated with increased virulence.