Carriage of methicillin-resistant Staphylococcus aureus at hospital admission.

OBJECTIVES: To measure the prevalence of, and to establish predictors for, the nasal carriage of methicillin-resistant Staphylococcus aureus (MRSA) at hospital admission. To evaluate mannitol-salt agar with oxacillin for the simultaneous detection and identification of MRSA from nasal swabs. DESIGN: Three-month prospective case-control survey, with data collected from interviews and computerized databases. The criterion standard for MRSA detection was culture on Mueller-Hinton agar with oxacillin 6 microg/mL (National Committee for Clinical Laboratory Standards method). SETTING: 320-bed tertiary-care hospital. PATIENTS: 387 patients screened within 24 hours after admission, including 10 MRSA carriers (cases), 291 patients with no S aureus, and 86 patients with methicillin-susceptible S aureus. RESULTS: The prevalence of MRSA nasal carriage was 2.6%, whereas the prevalence of carriage was 3.1% when both nasal and wound cultures were performed. The significant predictors of carriage were a prior detection of MRSA, open wounds, diabetes mellitus, treatments by injection, prior nursing home stays, visits at home by a nurse, and prior antibiotic treatments. Cases had stayed for longer periods in hospitals and had received longer antibiotic treatments within a year. Eighty patients (including the 10 cases) had diabetes, had been exposed to healthcare facilities within a year, and had antibiotics within 6 months. The sensitivity and negative predictive value of nasal swabs on mannitol-salt agar with oxacillin were 60% and 71%, respectively. CONCLUSION: MRSA carriage on admission to the hospital may be an increasing and underestimated problem. Further studies are needed to develop and validate a sensitive and specific prediction rule.

Failure of quality control measures to prevent reporting of false resistance to imipenem, resulting in a pseudo-outbreak of imipenem-resistant Pseudomonas aeruginosa.

False results showing an outbreak of Pseudomonas aeruginosa with resistance to imipenem were traced to a defective lot of microdilution MIC testing panels. These panels contained two- to threefold lower concentrations of imipenem than expected and resulted in artifactual two- to fourfold increases in MICs of imipenem. The quality-control MIC results for Pseudomonas aeruginosa ATCC 27853 were 4 microg/ml, the highest value within the range recommended by the National Committee for Clinical Laboratory Standards. We recommend that this value be considered out of the quality-control range.

Administrative support team. A structural innovation.

In response to societal, organization, and leadership changes, an innovative nursing structure was implemented and evaluated. An administrative support team was developed to provide specialized internal consultation and support to a flattened and decentralized nursing division. The four administrative support team roles provided an organization perspective that ensured constancy of purpose throughout the division. This structural innovation proved to be congruent with nursing shared governance and total quality management initiatives occurring in the organization. Evaluation studies indicated that the model has effectively supported 5 years of continuing organizational change.

Multicenter evaluation of a new enzyme immunoassay for detection of Clostridium difficile enterotoxin A.

The Premier Clostridium difficile toxin A enzyme immunoassay (PTA EIA) (Meridian Diagnostics, Inc., Cincinnati, Ohio) for rapid diagnosis of antibiotic-associated colitis (AAC) was evaluated in a multicenter study. Stool samples from 421 patients suspected of having AAC were tested for toxin A by the PTA EIA and for toxin B by three tissue culture assays (TCA) employing WI-38 cells (New England Deaconess Hospital) in conventional tubes or foreskin fibroblasts (Children's Hospital) or Vero cells (Beth Israel Hospital) in microwells. The tubes and plates were examined at 24 and 48 h for cytotoxicity. Clinical criteria, repeat testing at another site, and culture of frozen stool samples for C. difficile were used to evaluate discrepant results. Of 504 samples, 66 were positive and 409 were negative by both tests. Eight samples had indeterminate PTA EIA results and were excluded from this analysis. Of 21 discrepancies, 9 were PTA EIA positive and TCA negative and 12 were PTA EIA negative TCA positive. Following resolution of the discrepancies, 11 of 12 PTA EIA-negative-TCA-positive and 5 of 9 PTA EIA-positive-TCA-negative samples were considered true positive for AAC. The sensitivity and specificity were, respectively, 86.6 and 99.0% for the PTA EIA and 93.9 and 99.8% for TCA. The predictive values of positive and negative tests were, respectively, 94.7 and 97.4% for the PTA EIA and 98.7 and 98.8% for TCA. We conclude that the PTA EIA is a rapid, simple EIA technique whose accuracy in detecting enterotoxin A approaches that of reference TCA methods for detection of cytotoxin B.

Evaluation of diagnostic methods for Helicobacter pylori gastritis.

The authors evaluated the use of direct Gram-stained smears, 1- and 24-hour urease broth tests, histologic examination, and culture to detect Helicobacter pylori in 100 gastric biopsy specimens from 97 patients with epigastric symptoms. Twenty-six patients had positive cultures and 27 had H. pylori identifiable in hematoxylin and eosin-stained sections. The gastric biopsy specimens from the 29 patients with culture and/or histologic findings positive for H. pylori showed active gastritis in 27 cases (93%), compared with 26 cases (37%) without H. pylori (P less than 0.0001). Chronic gastritis was present in 25 cases (86%) with H. pylori and 40 cases (56%) without H. pylori (P less than 0.01). Twenty patients had positive Gram-stained smears. Fifteen patients had positive 1-hour urease tests, and 3 had delayed positive 24-hour urease tests. There were no false-positive Gram's stain results, three false-positive 24-hour urease tests, two false-negative histologic results, and three false-negative cultures (one inadvertently incubated anaerobically). The sensitivities of the methods were as follows: 62% for the 24-hour urease test, 69% for direct Gram's stain, 90% for culture, and 93% for histologic examination. The authors conclude that the urease test used in this study has low sensitivity and limited specificity; that the direct Gram-stained smear is a useful, highly specific, rapid screening test; and that the lengthier methods of culture and histologic examination have comparably high sensitivity for the definitive diagnosis of H. pylori gastritis.

A comparison of the identification of group A streptococci and enterococci by two rapid pyrrolidonyl aminopeptidase methods.

Group A streptococci and enterococci can be differentiated from other streptococci by their ability to cleave L-pyrrolidonyl-beta-napthylamide (PYR). The authors evaluated two pyrrolidonyl aminopeptidase (PYRase) systems--Minitek (BBL Microbiology Systems, Cockeysville, MD) and Identicult-AE (Scott Laboratories, Inc., Fiskeville, RI)--for the presumptive identification of Group A streptococci and enterococci. Eighty-three Group A streptococci, 77 beta-hemolytic non-Group A streptococci, 74 enterococci, 56 nonenterococcal non-beta-hemolytic streptococci, 1 Streptococcus pneumoniae, and 1 Aerococcus were tested. Compared with results obtained with reference methods (bile esculin agar and 6.5% [w/v] sodium chloride for identification of enterococci, and latex agglutination tests by Streptex [Burroughs Wellcome, NC] for grouping of beta-hemolytic streptococci) both the Identicult-AE and MInitek systems were 100% sensitive and specific for identification of both enterococci and Group A beta-hemolytic streptococci. Advantages of the Identicult-AE system compared with Minitek were the use of a smaller inoculum for which subculture was not necessary, incubation at room temperature rather than at 37 degrees C, and lower cost. Both PYRase kits tested, and in particular the Identicult-AE system, were very easy to use and should be considered as rapid, reliable, and cost-effective alternative methods for the presumptive identification of Group A streptococci and enterococci in the clinical laboratory.

Evaluation of the IDS RapID SS/u system for rapid identification of urinary microorganisms.

The accuracy of a new rapid identification system for common urinary pathogens was compared with that of conventional methods and of miniaturized 18-24-hour identification panels. The rapid system, RapID SS/u (Innovative Diagnostic System Inc., Atlanta, GA) is a non-growth-dependent micro-method that identifies selected gram-negative bacilli, gram-positive cocci, and yeasts in two hours by detection of constitutive enzymes acting on chromogenic substrates. A total of 185 representative clinical urinary isolates were tested, including 24 gram-positive cocci, 140 gram-negative bacilli, and 21 yeasts. Identifications by the rapid system were compared with the ones obtained by reference conventional methods for gram-positive cocci and yeasts. For gram-negative bacilli, identifications were compared with the ones obtained by MicroScan Combo Panel (American MicroScan, Mahwah, NJ), and all discrepancies were resolved by testing with API 20E (Analytab Products, Plainview, NY). Overall, the RapID SS/u system correctly identified to genus 160 of 185 isolates (86.5%). For 14 additional isolates (7.6%) the system provided probability overlap identifications that required further testing. Two (1%) isolates failed to be identified, and nine isolates (4.9%) were misidentified by the system. Discrepancies involved five strains of Citrobacter, one Enterobacter, one Morganella, and one Providencia species. The authors conclude that the RapID SS/u system provided rapid and accurate genus identification of most microorganisms commonly isolated from urine.

Evaluation of a new latex agglutination method for detection of antibody to herpes simplex virus.

A new latex agglutination (LA) test (Wampole Laboratories, Cranbury, N.J.) for detection of antibody to herpes simplex virus was compared with a reference complement fixation (CF) method in a premarket evaluation. Of 102 serum samples tested, 19 were LA negative and CF negative, 79 were LA positive and CF positive, and 4 were LA positive and CF negative. An enzyme immunoassay (M. A. Bioproducts, Walkersville, Md.) performed on the four LA-positive and CF-negative serum samples agreed with LA in all cases. Most LA titers were two to four doubling dilutions higher than CF titers. We conclude that this new LA test is a rapid, sensitive, and simple method for documentation of past infection with herpes simplex virus.

Rapid detection of cytomegalovirus in clinical specimens by immunofluorescent staining of shell vial cultures.

A recently described rapid technique for detection of cytomegalovirus (CMV) was evaluated in clinical specimens utilizing indirect immunofluorescent staining (IFA) of shell vial cultures. A total of 266 clinical specimens received for viral isolation were inoculated to commercially available shell vials seeded with human lung fibroblasts (MRC-5), centrifuged at 700 X g for one hour, and stained after 18 hours incubation with monoclonal antibody to CMV early nuclear protein (Biotech Research Laboratories) and fluorescein conjugated goat antimouse IgG (Cappel Laboratories). All specimens were also inoculated to tubes of human lung fibroblasts and observed for cytopathic effect (CPE) for 28 days. Of 54 specimens positive for CMV, 36 were positive by both IFA and CPE, 3 were positive by CPE only, and 15 were positive by IFA only (P less than 0.01 by the chi-square test). Failure to detect CMV associated CPE in 10 of these 15 samples was probably due to concomitant infection with herpes simplex virus or heavy bacterial or fungal contamination. Nine of the 13 patients with IFA-positive CPE-negative specimens had CMV infection documented by other positive cultures. It was concluded that the shell vial IFA rapid technique for detection of CMV is highly specific, more sensitive than conventional isolation, and well suited for application in a clinical virology laboratory.

Evaluation of a latex agglutination test for diagnosis of Clostridium difficile-associated colitis.

Current methods for diagnosis of Clostridium difficile-associated colitis (CAC) based on detection of cytotoxin B by a tissue culture assay (TCA) require technical expertise and up to 48 hours incubation. Recently, a latex agglutination (LA) test (Marion Laboratories) for rapid diagnosis of CAC has become available. Although early evaluations have been favorable, new evidence suggests that the LA reagent binds a soluble bacterial antigen that is not unique to toxigenic strains of C. difficile. The authors examined 201 stools received for CAC testing by LA and a reference TCA and investigated discrepant results. They obtained 29 LA(+)/TCA(+) and 155 LA(-)/TCA(-) results. Eleven patients had LA(+)/TCA(+) and 155 LA(-)/TCA(-) results. Eleven patients had LA(+)/TCA(-) results and 6 had LA(-)/TCA(+) results. The sensitivity and specificity of the LA were 83% and 93%, respectively, compared with TCA. The predictive values of positive and negative results obtained with the LA were 72% and 96%, respectively. Concentrated broth supernatants and live suspensions of three C. difficile isolates with LA(+)/TCA(-) results were tested in a rabbit ileal loop assay. All failed to demonstrate ability to produce an enterotoxin. The authors conclude that the LA method is suitable for rapid screening, but LA(+) results require confirmation by testing with other methods.

Detection of bacteremia with the BACTEC 16B resin blood culture medium.

A new blood culture medium (16B) containing adsorbent and cationic exchange resins has become available for use with the BACTEC instrument (Johnston Laboratories, Towson, MD). Its purpose is to enhance the detection of bacteremia through binding of antimicrobials. The performance of the BACTEC 16B resin medium was compared with the routine BACTEC 6B medium in patients with suspected sepsis receiving antibiotics. A total of 1,227 blood specimens were inoculated in 6B and 16B media and yielded 93 positive cultures from 43 clinically septic patients. Of 103 bacterial isolates recovered, 63 (61.2%) were recovered in both media, 14 (13.6%) in the routine 6B medium only, and 26 (25.2%) in the resin medium only (P greater than 0.05). Staphylococci, both coagulase positive and negative, were recovered much more frequently in resin medium (P less than 0.01). When the results of all the blood culture sets collected for each patient on any given day were considered, the routine 6B medium was the only source of isolation for seven bacterial species in six patients, and the resin medium was the only source of isolation for nine species in nine patients. However, of the nine organisms whose sole isolation source was the resin medium, eight were recovered early in the course of antibiotic therapy (6 within 24 to 36 hours and 2 within 36 to 48 hours of the first antibiotic dose) and had been isolated previously in routine 6B medium. In no instance was the antibiotic regimen changed as a result of the persistence of the organism in resin medium in the early phases of treatment. The use of resin medium did not improve overall detection time for 63 isolates recovered in both media. In conclusion, although the 16B resin medium did recover a greater number of bacterial isolates, it contributed very little information that might be of use in modifying and improving the treatment of septic patients receiving antimicrobials.

Evaluation of the AutoSCAN-3, a device for reading microdilution trays.

The AutoSCAN-3 (American MicroScan, Mahwah, N.J.) is an instrument capable of automated reading of commercially available microdilution trays for identification and quantitative susceptibility testing of rapidly growing bacteria. This study compared the results of visual and automated reading of microdilution trays for determination and interpretation of minimum inhibitory concentrations of 471 selected gram-negative and gram-positive clinical bacterial isolates. Visual and automated readings were performed in a double-blind fashion, and all discrepancies were examined by a referee. A quantitative comparison of minimum inhibitory concentrations was performed for 201 organisms, yielding 2,472 drug-organism combinations. After exclusion of off-scale values, complete quantitative agreement was obtained in 94% of 959 on-scale combinations, and agreement within +/- 1 well was obtained in 99.3%. Considering the minimum inhibitory concentration interpretations routinely furnished by the instrument, a qualitative comparison was performed for all 471 organisms. Complete agreement in interpretation was obtained in 97.6% of 5,843 drugs-organism combinations, with very major discrepancies accounting for only 0.1% and major discrepancies accounting for 0.2% of all combinations tested.

Evaluation of two sterility testing methods for intravenous admixtures.

The Addi-Chek Quality Control System (Millipore Corporation) and Ivex-2 Filterset (Abbott Laboratories) were evaluated to determine their effectiveness, applicability, and cost as part of a pharmacy quality-control program. Each method was tested using 50 solutions, 25 of which had been contaminated by inoculation with one of five micro-organisms; the other 25 solutions were used as controls. Aseptic technique was used, and procedures were carried out in a laminar air flow hood. Contaminated solutions were blinded from the person performing the tests. Addi-Chek detected contamination in all the inoculated solutions and in three of the uninoculated solutions. The latter may have been a result of adventitious contamination during the testing procedure. Ivex-2 detected contamination in 24 of the 25 inoculated solutions; no other contamination was found. The effectiveness of the methods in detecting low-level microbial contamination appears comparable. Both methods have been shown to be useful in the pharmacy setting, but Ivex-2 could be used to test for contamination when used as an in-line filter at the patient level. Ivex-2 is less expensive and warrants further evaluation in monitoring for microbial contamination during preparation and administration of intravenous solutions.