Epidemiological and biological characteristics of Methicillin-Resistant staphylococcal infections in a Mexican Hospital

RESUMO

Background. Methicillin-resistant Staphylococcus aureus (MRSA) has spread worldwide since 1960. However, there is little information concerning methicillinresistant coagulase-negative staphylococci (MRCNS) infections. Methods. In order to study the clinical and epidemiological characteristics of methicillinresistant staphylococci (MRS) infections and to determine the relationship between MRS and both synergistic hemolysis (SH) and slime production (SP), a laboratory-based survey and non-matched case-control study were carried out at a tertiary-care center in Mexico City. In regard to patients, from May 1991 to October 1992, 46 cases of MRS infection and 86 patients (controls) infected by methicillin-susceptible staphylococci (MSS) were included. Clinical and epidemiologic variables were analyzed. The isolates were identified and tested for antimicrobial susceptibility by standard method. An MIC of oxacillin = 8 µg/mL was defined as an MRS. Results. During the study. 94 nosocomial staphyloccocal infections were diagnosed S. aureus, 35 and CNS, 59; 43 (45.7 percent) by MRS (rate of MRS infections was 1.12 per 100 inpatients); 2 MRSA; 41 MRCNS, and only 19 were symptomatic. Three infections were community-acquired, including one MRSA and two MRCNS. After multivariate analysis, the significant risk factors were previous antimicrobial therapy (p= 0.013) and catheterelated (p= 0.009) and urinary-tract source (p = 0.0001). Forty-nine percent of MRS showed SH while only 15 percent of MSS (p < 0.001) showed SH, especially in 10/10 MR-S. hemolyticus. additionally, 48 percent of MRCNS showed SP, as did 18 percent of MSCNS (p = 0.019), particularly in 15/20 MR-S. epidermis. Of all MRS isolates, 38 percent showed a homogeneous phenotype, a trait associated with multi-durg resistance (p < 0.01) and SH (p< 0.001). Conclusions. CNS predominanted as the cause of MRS infections in our setting. The homogeneous phenotype was associated with SH and multi-drug resistance