Jan Evans Patterson

The evolving epidemiology of methicillin-resistant Staphylococcus aureus at a university hospital.

OBJECTIVE To describe the epidemiology of methicillin-resistant Staphylococcus aureus (MRSA) at a university hospital during a 14-month period. DESIGN Prospective laboratory-based surveillance for MRSA with descriptive epidemiology based on medical chart review and characterization of strains by DNA typing, using pulsed-field gel electrophoresis (PFGE). SETTING An 850-bed tertiary care university hospital. PATIENTS Patients with clinical isolates of MRSA. MAIN OUTCOME MEASURE Determination whether MRSA isolates were community- or hospital-related. RESULTS Among 87 patients with MRSA, 36 (41%) had community-acquired infections. Community acquisition was associated with recent hospitalization, previous antibiotic therapy, nursing home residence, and intravenous drug use. Greater than 3 months had elapsed from the time of discharge for 13 (62%) of the 21 patients with community-acquired isolates hospitalized within the last year. Eight patients (22%) with community-acquired MRSA had no discernible risk factors. PFGE allowed differentiation of 35 distinct whole-cell DNA patterns; heterogeneity was seen among both nosocomial and community-acquired isolates, with few instances of cross-transmission. CONCLUSIONS Our data suggest an increase in community acquisition of MRSA. PFGE demonstrated heterogeneity of MRSA isolates from both the community and the hospital setting.

Association of contaminated gloves with transmission of Acinetobacter calcoaceticus var. anitratus in an intensive care unit

PURPOSE Acinetobacter calcoaceticus var. anitratus is an important nosocomial pathogen that has been associated with environmental reservoirs. An increased isolation rate of A. anitratus in our intensive care units (ICUs), from 0.03% (two of 7,800) to 0.5% (seven of 1,300) (p less than 0.00003), prompted an investigation. PATIENTS, METHODS, AND RESULTS Ten patients were admitted to the surgical ICU and nine to the medical ICU during the outbreak period (late December 1987 to January 1988). Controls were all patients on the units who were not infected or colonized with the transmitted strain of A. anitratus. Three patients had A. anitratus pneumonia. A throat culture prevalence survey demonstrated three patients colonized with A. anitratus. Cases were placed in a cohort and symptomatic cases treated. An epidemiologic investigation was conducted to identify reservoirs and modes of transmission. Latex gloves were being used for universal precautions without routine changing of gloves between patients. Environmental sources culture-positive for A. antitratus included a small volume medication nebulizer and gloves in use for patient care. Plasmid typing showed that plasmid profiles of isolates from two symptomatic patients, two colonized patients, the nebulizer, and the gloves were identical. Other A. anitratus ICU isolates had distinct plasmid profiles. All patients with the transmitted strain had been in the surgical ICU. The need for changing gloves between patients and contaminated body sites was reinforced. CONCLUSION Gloves, used incorrectly for universal precautions, may potentially transmit A. anitratus.

Hospital epidemiologic surveillance for invasive aspergillosis : Patient demographics and the utility of antigen detection

OBJECTIVE To monitor the epidemiology of invasive aspergillosis at a university hospital during a period of hospital construction. To compare the efficacy of active epidemiologic surveillance for invasive aspergillosis using Aspergillus cultures with the efficacy of surveillance using Aspergillus antigen detection. DESIGN A prospective surveillance study. SETTING An 850-bed, tertiary-care, university-based hospital. PATIENTS A convenience sample of 153 patients with Aspergillus antigen testing and culture. RESULTS 24 cases were identified over a 12-month period; 7 were nosocomial, and 17 were community-acquired. Cases occurred primarily in patients with hematologic malignancy, but also occurred in patients with solid tumor, steroid treatment, cardiac transplant, and acquired immunodeficiency syndrome. Culture techniques identified only 14 (58%) of 24 cases, whereas Aspergillus antigen was positive in 19 (79%) of 24 cases tested. Epidemiological surveillance using either antigen or culture positivity detected 22 (92%) of 24 cases. In addition, antigen detection was 98% specific for the detection of aspergillosis, as compared to 91% for culture and 88% for antigen and culture combined. CONCLUSIONS Hospital surveillance for aspergillosis should include determination of whether cases are nosocomial or community-acquired, because many may be the latter. Patients at risk for aspergillosis include patients without hematologic malignancies. Enhanced case detection occurred with active surveillance of patients considered to be at risk using both fungal serology and traditional microbiological techniques. Antigen detection was more sensitive and specific for the detection of invasive aspergillosis and may improve epidemiological surveillance for aspergillosis.

Molecular characterization of highly gentamicin-resistant Enterococcus faecalis isolates lacking high-level streptomycin resistance.

Antimicrobial susceptibilities and DNA contents were analyzed for six clinical isolates of Enterococcus faecalis that had high-level resistance to gentamicin (MIC > 2,000 micrograms/ml) but not streptomycin and were obtained from patients in diverse geographic areas. Contour-clamped homogeneous electric field electrophoresis of genomic DNA showed all isolates to be different strains. Gentamicin resistance was transferred from four isolates to plasmid-free enterococcal recipients in filter matings. Restriction enzyme analysis of transconjugants showed distinct gentamicin resistance plasmids. A probe specific for the gentamicin resistance determinant hybridized to the plasmids of four isolates and to the chromosomes of two isolates. These findings suggest that clonal dissemination is not responsible for the spread of these resistant strains, that resistance determinants occur on different plasmids as well as on the chromosome of E. faecalis, and that the genetic determinants of resistance are related. Images

Characterization and comparison of two penicillinase-producing strains of Streptococcus (Enterococcus) faecalis.

We identified two beta-lactamase-positive enterococci. One strain was high-level (MIC, greater than 2,000 microgram/ml) gentamicin resistant; the other was not (MIC, 12.5 microgram/ml). beta-Lactamase production was extrachromosomally mediated in both strains, and both strains showed an inoculum effect reversed by beta-lactamase inhibitors. The strain lacking high-level gentamicin resistance showed synergistic killing with a combination of penicillin, clavulanic acid, and gentamicin.

Susceptibility and bactericidal activity studies of four β-Lactamase-producing enterococci

beta-Lactamase-producing (Bla+) enterococci are rare but have been reported from several areas. We report another Bla+ enterococcus with high-level gentamicin resistance. Susceptibility and bactericidal activity studies of four Bla+ enterococci against potential alternative antibiotics, including ampicillin-sulbactam, daptomycin, teicoplanin, and vancomycin, are presented.

Time-kill kinetic studies of ampicillin/sulbactam for β-Lactamase-producing enterococci☆

beta-Lactamase-producing (Bla+) enterococci have now been reported from several geographic areas. Most of these strains also demonstrate high-level aminoglycoside resistance, making therapy of serious infections due to Bla+ enterococci difficult. Using time-kill kinetic studies, we evaluated the activity of ampicillin-sulbactam (Am/SB) against five clinical Bla+ Enterococcus faecalis isolates from three geographically distinct areas. Am at fourfold minimum inhibitory concentrations (MIC) concentrations did not achieve bactericidal activity as determined by time-kill kinetic studies. Am/SB achieved 99.9% reduction in growth at 24 hr at twofold MIC concentrations without an aminoglycoside in four of five strains. SB alone had little independent activity against any of the strains, but synergy of killing was achieved in all five strains with a combination of Am + SB. No synergy was shown in a Bla- control strain. Am/SB may be useful for serious infections due to Bla+ enterococci.