Comparison of Etest method with reference broth microdilution method for antimicrobial susceptibility testing of Yersinia pestis.

The utility of Etest for antimicrobial susceptibility testing of Yersinia pestis was evaluated in comparison with broth microdilution and disk diffusion for eight agents. Four laboratories tested 26 diverse strains and found Etest to be reliable for testing antimicrobial agents used to treat Y. pestis, except for chloramphenicol and trimethoprim-sulfamethoxazole. Disk diffusion testing is not recommended.

Administrative coding data and health care-associated infections.

Surveillance for health care-associated infections (HAIs) using administrative data has received attention from health care epidemiologists searching for efficient means to track infections in their institutions. Several states are also considering electronic surveillance that incorporates administrative data as a means to satisfy an increasing demand for mandatory public reporting of HAIs. International Classification of Diseases, Ninth Revision, Clinical Modification (ICD-9-CM) discharge diagnosis codes have attributes that make them suitable for detecting HAIs; for example, they may facilitate automated surveillance, freeing up infection control personnel to perform other important tasks, such as staff education and outbreak investigation. However, controversy surrounds the appropriate use of ICD-9-CM data in detecting HAIs, and administrative coding data have been criticized for lacking elements necessary for surveillance. Administrative coding data are inappropriate as the sole means of HAI surveillance but may have value to the health care epidemiologist as a way to augment traditional methods.

Structural analysis of biofilm formation by rapidly and slowly growing nontuberculous mycobacteria.

Mycobacterium avium complex (MAC) and rapidly growing mycobacteria (RGM) such as M. abscessus, M. mucogenicum, M. chelonae, and M. fortuitum, implicated in health care-associated infections, are often isolated from potable water supplies as part of the microbial flora. To understand factors that influence growth in their environmental source, clinical RGM and slowly growing MAC isolates were grown as biofilm in a laboratory batch system. High and low nutrient levels were compared, as well as stainless steel and polycarbonate surfaces. Biofilm growth was measured after 72 h of incubation by enumeration of bacteria from disrupted biofilms and by direct quantitative image analysis of biofilm microcolony structure. RGM biofilm development was influenced more by nutrient level than by substrate material, though both affected biofilm growth for most of the isolates tested. Microcolony structure revealed that RGM develop several different biofilm structures under high-nutrient growth conditions, including pillars of various shapes (M. abscessus and M. fortuitum) and extensive cording (M. abscessus and M. chelonae). Although it is a slowly growing species in the laboratory, a clinical isolate of M. avium developed more culturable biofilm in potable water in 72 h than any of the 10 RGM examined. This indicates that M. avium is better adapted for growth in potable water systems than in laboratory incubation conditions and suggests some advantage that MAC has over RGM in low-nutrient environments.

RETRACTED: Structural analysis of biofilm formation by rapidly and slowly growing nontuberculous mycobacteria.

This article has been retracted.

Investigation of postoperative allograft-associated infections in patients who underwent musculoskeletal allograft implantation.

BACKGROUND: The rate at which allografts are used in surgical procedures has doubled in the United States during the past decade. In 2002, one outpatient surgical center (SC-X) identified a cluster of surgical site infections (SSIs) after anterior cruciate ligament reconstructive surgery (ACLRS). Therefore, we conducted an investigation to determine the extent of the outbreak and to identify risk factors. METHODS: Our investigation included retrospective cohort and observational studies. A case patient was defined as any patient who acquired a SSI after undergoing ACLRS at SC-X between February 2000 and June 2002 (the study period). Data collected included demographic characteristics, clinical information, and graft details, such as processing method (i.e., aseptic or sterile). RESULTS: Of 331 patients who underwent ACLRS during the study period, 11 (3.3%) met the case definition. All infections occurred at the tibial fixation site of the graft and involved 8 different microorganisms; the median time to a positive culture result was 55 days after ACLRS. The infection rate for patients who received aseptically processed allografts was 4.4% (11 of 250 patients), compared with 0% (0 of 81) for patients who received autografts or sterile allografts (P=.07). Use of a supplementary staple for tibial fixation, compared with other fixation methods that did not involve such staples, increased the risk of infection 10-fold in univariate analysis (relative risk [RR], 10.0; 95% confidence interval [CI], 3.0-32.9) and 9-fold when controlling for tissue processing method (RR, 9.0; 95% CI, 2.8-28.8). CONCLUSIONS: The use of sterile allograft tissue appears to be associated with a significant reduction in the risk of postoperative infection, particularly in the presence of adjunctive fixation. Larger clinical studies are necessary to confirm this observation.

Swab materials and Bacillus anthracis spore recovery from nonporous surfaces.

Four swab materials were evaluated for their efficiency in recovery of Bacillus anthracis spores from steel coupons. Cotton, macrofoam, polyester, and rayon swabs were used to sample coupons inoculated with a spore suspension of known concentration. Three methods of processing for the removal of spores from the swabs (vortexing, sonication, or minimal agitation) and two swab preparations (premoistened and dry) were evaluated. Results indicated that premoistened swabs were more efficient at recovering spores than dry swabs (14.3% vs. 4.4%). Vortexing swabs for 2 min during processing resulted in superior extraction of spores when compared to sonicating them for 12 min or subjecting them to minimal agitation. Premoistened macrofoam and cotton swabs that were vortexed during processing recovered the greatest proportions of spores with a mean recovery of 43.6% (standard deviation [SD] 11.1%) and 41.7% (SD 14.6%), respectively. Premoistened and vortexed polyester and rayon swabs were less efficient, at 9.9% (SD 3.8%) and 11.5% (SD 7.9%), respectively.

Secular trends in hospital-acquired Clostridium difficile disease in the United States, 1987-2001.

We reviewed Clostridium difficile-associated disease (CDAD) data from the intensive care unit (ICU) and hospital-wide surveillance components of the National Nosocomial Infections Surveillance System hospitals during 1987-2001. ICU CDAD rates increased significantly only in hospitals with >500 beds (P<.01) and correlated with the duration of ICU stay (r=0.82; P<.05). Hospital-wide (non-ICU) rates increased only in hospitals with <250 beds (P<.01) and in general medicine patients versus surgery patients (P<.0001). CDAD predominated in general hospitals versus other facility types, and rates were significantly higher during winter versus nonwinter months (P<.01). Thus, prevention efforts should be targeted to high-risk groups in these settings.

Optimization of computer software settings improves accuracy of pulsed-field gel electrophoresis macrorestriction fragment pattern analysis.

Computer-assisted analysis of pulsed-field gel electrophoresis (PFGE) libraries can facilitate comparisons of fragment patterns present on multiple gels. We evaluated the ability of the Advanced Analysis (version 4.01) and Database (version 1.12) modules of the Phoretix gel analysis software package (Nonlinear USA, Inc., Durham, N.C.) to accurately match DNA fragment patterns. Two gels containing 38 lanes of SmaI-digested Enterococcus faecalis OG1RF DNA were analyzed to assess the impact of (i) varying the lane position of the standards, (ii) using gel plugs made at different times, and (iii) normalizing the fragment patterns by using molecular weight (MW) algorithms versus retardation factor (R(f)) algorithms. Two sets of PFGE libraries (one containing SmaI restriction patterns from 62 Enterococcus faecium isolates and the other containing SmaI restriction patterns of 89 Staphylococcus aureus isolates) were analyzed to assess the impact of varying the matching tolerance algorithm (designated as the vector box setting [VBS]) in the Phoretix software. Varying the lane position of standards on a gel and using gel plugs made on different days resulted in different VBSs, although it was not possible to judge whether those differences were statistically significant. Normalization of E. faecalis OG1RF fragment patterns by R(f) and MW methodology yielded no statistically significant differences in variability between the same fragment on different lanes. Suboptimal VBSs decreased the specificity with which related isolates were grouped together in dendrograms. The optimal VBS for analysis of PFGE fragment patterns from E. faecalis isolates differed from that for S. aureus isolates and sometimes was not that recommended by the manufacturer. Thus, computer-assisted analysis of PFGE patterns seemed to compensate for the intra- and intergel variation evaluated in the present study, and optimizing the software for the species to be tested was a critical preliminary step before further PFGE library analysis.

Survival of Yersinia pestis on environmental surfaces.

The survival of two strains of Yersinia pestis (avirulent A1122 and virulent Harbin) on the surfaces of four materials was investigated. Viability was evaluated with epifluorescence microscopy by using the metabolic stain cyanoditolyl tetrazolium chloride and plate counts. Small numbers of cells suspended in phosphate buffer survived 2 to 4 h after visible drying on stainless steel, polyethylene, or glass and beyond 48 h on paper. Cells suspended in brain heart infusion broth (BHI) persisted more than 72 h on stainless steel, polyethylene, and glass. Small numbers of cells suspended in BHI were still viable at 120 h on paper. These data suggest that Y. pestis maintains viability for extended periods (last measured at 5 days) under controlled conditions.

Prevalence of surgical-site infections and patterns of antimicrobial use in a large tertiary-care hospital in Ho Chi Minh City, Vietnam.

BACKGROUND: Few studies have been conducted in Vietnam on the epidemiology of healthcare-associated infections or antimicrobial use. Thus, we sought to determine the prevalence of and risk factors for surgical-site infections (SSIs) and to document antimicrobial use in surgical patients in a large healthcare facility in Vietnam. METHODS: We conducted a point-prevalence survey of SSIs and antimicrobial use at Cho Ray Hospital, Ho Chi Minh City, a 1,250-bed inpatient facility. All patients on the 11 surgical wards and 2 intensive care units who had surgery within 30 days before the survey date were included. RESULTS: Of 391 surgical patients, 56 (14.3%) had an SSI. When we compared patients with and without SSIs, factors associated with infection included trauma (relative risk [RR], 2.65; 95% confidence interval [CI95], 1.60 to 4.37; P < .001), emergency surgery (RR, 2.74; CI95, 1.65 to 4.55; P < .001), and dirty wounds (RR, 3.77; CI95, 2.39 to 5.96; P < .001). Overall, 198 (51%) of the patients received antimicrobials more than 8 hours before surgery and 390 (99.7%) received them after surgery. Commonly used antimicrobials included third-generation cephalosporins and aminoglycosides. Thirty isolates were identified from 26 SSI patient cultures; of the 25 isolates undergoing antimicrobial susceptibility testing, 22 (88%) were resistant to ceftriaxone and 24 (92%) to gentamicin. CONCLUSIONS: Our data show that (1) SSIs are prevalent at Cho Ray Hospital; (2) antimicrobial use among surgical patients is widespread and inconsistent with published guidelines; and (3) pathogens often are resistant to commonly used antimicrobials. SSI prevention interventions, including appropriate use of antimicrobials, are needed in this population.