title: Increased rifampicin resistance in blood isolates of meticillin-resistant Staphylococcus aureus (MRSA) amongst patients exposed to rifampicin-containing antituberculous treatment.
abstract: The aim of this study was to determine the rifampicin (RIF) resistance rate of meticillin-resistant Staphylococcus aureus (MRSA) amongst patients with MRSA bacteraemia who have or have not been exposed to RIF-containing antituberculous (anti-TB) treatment. From 2000 to 2008, patients with MRSA bacteraemia and previous exposure to RIF-containing anti-TB therapy were selected. Patients matched for sex, age and time of culture of MRSA bacteraemia but without exposure to anti-TB therapy were selected as a control group. A total of 139 patients, comprising 49 with RIF exposure and 90 without RIF exposure, were analysed. The RIF resistance rate was higher in patients with previous RIF exposure (61.2% vs. 20.0%; P<0.001). The minimum inhibitory concentration of RIF that inhibited 50% of MRSA isolates (MIC(50)) for the study group was also higher (128 mg/L vs. 0.015 mg/L; P<0.001). The mortality rate was higher in the study group (59.2% vs. 41.1%; P=0.041). MRSA isolates recovered from patients with current usage of a RIF-containing anti-TB regimen were more likely to be resistant to RIF (87.5% vs. 36%; P=0.001), with higher MIC(50) values (256 mg/L vs. 1mg/L; P=0.002), and resulted in a higher mortality rate than isolates from patients with remote usage of an anti-TB regimen (79.2% vs. 40%; P=0.005). Multivariate analysis showed that current anti-TB drug usage was the only risk factor for RIF resistance [odds ratio (OR)=7.457, 95% confidence interval (CI) 1.581-35.167] and mortality (OR=7.201, 95% CI 1.583-32.766). Given the high rate of RIF resistance in patients with prior anti-TB treatment, RIF susceptibility testing should be performed before considering combination treatment of RIF in MRSA infection.
authors.affiliation: Department of Intensive Care Medicine, Chi Mei Medical Center, Yong Kang, Tainan, Taiwan.
authors.forename: Che-Kim
authors.initials: CK
authors.lastname: Tan
authors.forename: Chih-Cheng
authors.initials: CC
authors.lastname: Lai
authors.forename: Chun-Hsing
authors.initials: CH
authors.lastname: Liao
authors.forename: Sheng-Hsiang
authors.initials: SH
authors.lastname: Lin
authors.forename: Yu-Tsung
authors.initials: YT
authors.lastname: Huang
authors.forename: Po-Ren
authors.initials: PR
authors.lastname: Hsueh
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D000900:Anti-Bacterial Agents / Q000008:administration & dosage* / Q000494:pharmacology; D016470:Bacteremia / Q000382:microbiology*; D001769:Blood / Q000382:microbiology; D024881:Drug Resistance, Bacterial; D005260:Female; D006801:Humans; D008297:Male; D055624:Methicillin-Resistant Staphylococcus aureus / Q000187:drug effects* / Q000302:isolation & purification; D008826:Microbial Sensitivity Tests; D008875:Middle Aged; D012293:Rifampin / Q000008:administration & dosage* / Q000494:pharmacology; D013203:Staphylococcal Infections / Q000382:microbiology*; D014376:Tuberculosis / Q000150:complications* / Q000188:drug therapy*
chemical_list: D000900:Anti-Bacterial Agents; D012293:Rifampin