Clonal spread of methicillin-resistant Staphylococcus aureus in a large geographic area of the United States.

Methicillin resistance in Staphylococcus aureus has rapidly increased over the last two decades. This increase is paralleled by the emergence of unique multi-resistant MRSA clones. In Brazil, Argentina, Uruguay, Portugal and Czech Republic a specific MRSA clone is widely spread, the so-called Brazilian epidemic clone. Another epidemic clone, the Iberian clone, is disseminated in Spain, Portugal, Belgium, Scotland, Italy, Germany and New York. Thus, a large number of hospital-acquired infections have been caused by specific MRSA clones. Using different molecular techniques for MRSA typing, we verified that two unique epidemic clones are spread over large geographic area in the US. In addition, we showed that a previously described MRSA clone type, the New York clone (I::A:A), is widely spread beyond the New York frontiers.

Molecular epidemiology of vancomycin-resistant Enterococcus faecium in a large urban hospital over a 5-year period.

To investigate the dissemination of vancomycin-resistant Enterococcus faecium (VREF) in a 728-bed tertiary-care hospital, all clinical VREF isolates recovered from June 1992 to June 1997 were typed by pulsed-field gel electrophoresis, and the transfer histories of the patients were documented. A total of 413 VREF isolates from urine (52%), wounds (16%), blood (11%), catheter tips (6%), and other sites (15%) were studied. VREF specimens mostly came from patients on wards (66%) but 34% came from patients in an intensive care unit. The number of VREF isolates progressively increased over time, with higher rates of isolation during the winter months and lower rates in the late summer months. Four distinct banding patterns were detected by pulsed-field gel electrophoresis among 316 samples (76%). Strain A (122 samples; 30%) appeared in June 1992 as the first VREF strain and was found until December 1994 throughout the entire hospital. Type B (92 samples; 22%) was initially detected in January 1994 and disappeared in November 1996. Strain C (10 samples; 2%) was limited to late 1996 and early 1997. Strain D (92 samples; 22%) showed two major peaks during March 1996 to August 1996 and January 1997 to February 1997. Unrelated strains (97 samples; 24%) appeared 1 year after the appearance of the first VREF isolate, and the numbers increased slightly over the years. Nosocomial acquisition (i.e., no known detection prior to admission and first isolation from cultures performed with samples retrieved >/=2 days after hospitalization) was found for 316 (91%) of 347 patients. Despite the implementation of Centers for Disease Control and Prevention guidelines, the proportion of related strains and high number of nosocomial cases of infection indicate a high transmission rate inside the hospital. The results imply an urgent need for stringent enforcement of more effective infection control measures.

Clinical predictors of infection of central venous catheters used for total parenteral nutrition.

To identify predictors of infection in catheters used for total parenteral nutrition (TPN), clinical and microbiological data were prospectively collected on 169 catheter systems (88 patients). Based on semiquantitative catheter cultures, infection was associated with a positive insertion site skin culture taken close to the time of catheter removal (relative risk [RR] = 4.50), especially one yielding greater than or equal to 50 colonies of an organism other than coagulase-negative staphylococci. Infection was also associated with erythema at the insertion site greater than 4 mm in diameter (RR = 2.93). In a subset of 67 catheters for which blood cultures were obtained, infection was also associated with a positive peripheral venous blood culture (RR = 5.90) and a positive central venous blood culture obtained through the catheter (RR = 5.44). Based on a logistic regression model, periodic cultures of the insertion site should be useful in evaluating subsequent fever in stable patients with indwelling central venous catheters. Another source of fever is likely if inflammation is absent and there is either no colonization or there is colonization by less than 50 colonies of coagulase-negative staphylococci at the insertion site. Conversely, the catheter should be removed and cultured semiquantitatively if the site is colonized by an organism other than coagulase-negative staphylococci. We suggest that blood culture results add little to the risk estimate in these situations.

Prospective study of catheter replacement and other risk factors for infection of hyperalimentation catheters.

To determine risk factors for infection of hyperalimentation catheters, we prospectively studied 169 catheter systems (88 patients) by using a semiquantitative culture technique. Infection occurred in 24 (14%) catheters (16 patients), was inversely proportional to the number of previous catheters inserted by the operator (P less than .02), and was proportional to the interval between admission and catheter insertion (P less than .0005). Catheter replacement over a guidewire was no more likely to be associated with infection than was a de novo percutaneous insertion at another site (P = .6). Using a proportional hazards model, we estimated the risk of infection per day to be 1.3 times greater for a catheter if the patient had been hospitalized 50 days instead of seven days, and 3.8 times greater if the patient had a Swan-Ganz catheter at the time of insertion.

Microbial growth patterns in intravenous fat emulsions.

Microbial growth patterns were studied in intravenous fat emulsions under conditions that simulated touch contamination before or during administration. Commercially available emulsions of 10% and 20% soybean oil and 10% safflower oil in 500-ml bottles were inoculated with two concentrations of each of four organisms: a coagulase-negative Staphylococcus isolated from a venipuncture site, Escherichia coli, Pseudomonas aeruginosa, and Candida albicans. The bottles were kept at room temperature, and samples were taken by direct puncture of the i.v. port at 0, 3, 6, 12, 24, 48, and 72 hours, diluted, and plated. Emulsions were visually inspected daily. Growth of the coagulase-negative Staphylococcus was minimal for 48 hours. E. coli showed substantial growth within 12 hours in all three emulsions. Growth patterns for Ps. aeruginosa were similar in all emulsions, and growth approximated that of E. coli within 48 hours. The growth rate of C. albicans was intermediate between that of Staphylococcus and those of E. coli and Ps. aeruginosa. Growth of C. albicans was greater in 10% safflower oil emulsion than in the other emulsions. No physical changes were observed. The coagulase-negative Staphylococcus showed less growth than C. albicans, Ps. aeruginosa, and E. coli. Substantial growth within 12 hours was seen only with E. coli. C. albicans exhibited preferential growth in 10% safflower oil emulsion.

Evaluation of a device for monitoring sterility of injectable fluids.

An evaluation of a sterility-testing device (Addi-Chek) that uses total-sample membrane filtration is presented. Parenteral nutrition solutions were deliberately contaminated at low levels with 16 bacterial and four fungal strains. Some contaminated solutions were stored at 20 degrees C or 4 degrees C for up to 24 hours before testing; the rest were tested immediately. Additionally, one liter of pharmacy-prepared infusion fluid was tested each day for 100 days. Broth (added to the Addi-Chek unit after filtration to permit microbial growth) was cultured when it became turbid or after a 10-day incubation. Fifty-nine deliberate-inoculation tests were done. The organism was recovered from 56 of these; the other three tests may have been negative because no organisms were present in the aliquot used for inoculation or because of experimental error. The number of organisms used for inoculation varied from 1 to 80; 86% of the tests used 25 organisms or less. Storage for up to 24 hours at 20 degrees C and 4 degrees C had no effect on the results of sterility testing. In testing 100 units of pharmacy-prepared fluid (not deliberately contaminated), one unit (1%) was found to be contaminated. Pharmacy personnel correctly identified positive and negative Addi-Chek units based on visual turbidity of the broth. It is concluded that Addi-Chek is easy to use and effective in detecting low-level contamination in intravenous fluids.