Qinfang Qian

Methicillin-Resistant Staphylococcus aureus: Comparison of Susceptibility Testing Methods and Analysis of mecA-Positive Susceptible Strains

ABSTRACT Methicillin-resistant Staphylococcus aureus (MRSA) is responsible for an increasing number of serious nosocomial and community-acquired infections. Phenotypic heterogeneous drug resistance (heteroresistance) to antistaphylococcal beta-lactams affects the results of susceptibility testing. The present study compared the MRSA-Screen latex agglutination test (Denka Seiken Co., Ltd., Tokyo, Japan) for detection of PBP 2a with agar dilution, the VITEK-1 and VITEK-2 systems (bioMérieux, St. Louis, Mo.), and the oxacillin agar screen test for detection of MRSA, with PCR for themecA gene used as the “gold standard” assay. Analysis of 107 methicillin-susceptible S. aureus (MSSA) isolates and 203 MRSA isolates revealed that the MRSA-Screen latex agglutination test is superior to any single phenotype-based susceptibility testing method, with a sensitivity of 100% and a specificity of 99.1%. Only one isolate that lacked mecAwas weakly positive by the MRSA-Screen latex agglutination test. This isolate was phenotypically susceptible to oxacillin and did not contain the mecA gene by Southern blot hybridization. The oxacillin agar screen test, the VITEK-1 system, the VITEK-2 system, and agar dilution showed sensitivities of 99.0, 99.0, 99.5, and 99%, respectively, and specificities of 98.1, 100, 97.2, and 100%, respectively. The differences in sensitivity or specificity were not statistically significant. Oxacillin bactericidal assays showed thatmecA- and PBP 2a-positive S. aureusisolates that are susceptible to antistaphylococcal beta-lactams by conventional methods are functionally resistant to oxacillin. We conclude that the accuracy of the MRSA-Screen latex agglutination method for detection of PBP 2a approaches the accuracy of PCR and is more accurate than any susceptibility testing method used alone for the detection of MRSA.

Evaluation of the Abbott RealTime™ CT/NG assay in comparison to the Roche COBAS AMPLICOR CT/NG assay

ABSTRACT Several commercial methods exist for the molecular detection of Chlamydia trachomatis and Neisseria gonorrhoeae in clinical samples. Here we evaluated the performance characteristics of the newly FDA-cleared Abbott RealTime CT/NG assay (where “CT” stands for Chlamydia trachomatis and “NG” stands for Neisseria gonorrhoeae) that uses the automated m2000 molecular platform. Results were compared to those of the Roche Cobas Amplicor CT/NG assay. A total of 926 cervical swab, 45 female urine, 6 male urethral swab, and 407 male urine specimens from 1,384 patients were examined. After resolving all Roche N. gonorrhoeae-positive results with two additional real-time PCR assays, we found that the agreement between the assays was excellent. For urine samples, there was 99.6% positive agreement and 97.7% negative agreement for C. trachomatis, and for male urine samples, there was 100% positive agreement and 99.7% negative agreement for N. gonorrhoeae. For cervical swab samples, there was 98.8% positive agreement and 98.5% negative agreement for C. trachomatis, and there was 96.6% positive agreement and 99.8% negative agreement for N. gonorrhoeae. In limiting dilution analyses, we found that the Abbot assay was more sensitive than the Roche assay for both C. trachomatis and N. gonorrhoeae. In addition, there appeared to be an enhanced ability of the Abbott assay to detect dual infections, especially in the presence of large amounts of N. gonorrhoeae and small amounts of C. trachomatis organisms. In summary, we conclude that the Abbott RealTime CT/NG assay is an accurate and automated new addition to the available testing options for C. trachomatis and N. gonorrhoeae.

Rapid Identification of Staphylococcus aureus in Blood Cultures by Use of the Direct Tube Coagulase Test

ABSTRACT Direct tube coagulase testing for identification of Staphylococcus aureus from BACTEC culture broth showed a sensitivity, a specificity, and positive and negative predicative values of 34%, 100%, 100%, and 80.2% with 2 h of incubation and 65%, 98.7, 99.7%, and 88.6% with 4 h of incubation. Anaerobic blood culture contributed significantly to the detection of S. aureus.

Effective use of JC virus PCR for diagnosis of progressive multifocal leukoencephalopathy.

In a retrospective review of data from 168 patients with suspected progressive multifocal leukoencephalopathy (PML) between 1996 and 2006, JC virus (JCV) PCR on cerebrospinal fluid (CSF) samples was positive only in human immunodeficiency virus (HIV)-infected patients with low CD4 cell counts and in severely immunocompromised patients with radiographic lesions consistent with PML or infectious processes generally. Of note, one HIV patient with a very low CD4 cell count had a positive JCV PCR despite a normal magnetic resonance imaging exam. We concluded that JCV PCR testing on CSF specimens should therefore be targeted to these high-risk patients.

Direct Detection of Methicillin Resistance in Staphylococcus aureus in Blood Culture Broth by Use of a Penicillin Binding Protein 2a Latex Agglutination Test

ABSTRACT We studied the utility of performing a penicillin binding protein 2a latex agglutination (PBP-LA) assay directly on Bactec blood culture broth samples containing Staphylococcus aureus to rapidly detect methicillin resistance. The sensitivity, specificity, positive predictive value, and negative predictive value of this method were 94.1%, 97.5%, 98%, and 92.9%, respectively.

Optimal use of Myco/F Lytic and standard BACTEC blood culture bottles for detection of yeast and mycobacteria

CONTEXT The optimal use of dedicated fungal and mycobacterial blood culture bottles, such as the BACTEC Myco/F Lytic bottle, has not been well defined in clinical practice. OBJECTIVES To compare the performance of Myco/F Lytic and standard blood culture in clinical practice in an urban tertiary care hospital setting and to implement a strategy for optimal use of Myco/F Lytic culture. DATA SOURCES Retrospective review of laboratory records. RESULTS Myco/F Lytic culture did not increase detection of yeasts. Nor did it decrease time to detection except for Candida glabrata, where mean time to positivity dropped from 2.6 +/- 1.1 days in standard to 1.8 +/- 0.8 days in Myco/F Lytic culture. Therefore, an algorithm was developed in which Myco/F Lytic culture was reserved primarily for detection of mycobacteria in patients with severely depressed CD4 counts. Implementation of this algorithm led to a sustained 3-fold reduction in Myco/F Lytic blood culture usage. CONCLUSIONS Retrospective analysis suggests substantial clinical equivalence of standard blood and Myco/F Lytic culture for detection of yeast. A multifaceted educational approach based on this data led to a sustained change in physician ordering practices and more cost-effective use of resources.

Yield of primary and repeat induced sputum testing for Pneumocystis jiroveci in human immunodeficiency virus-positive and -negative patients

CONTEXT Induced sputum sampling has an approximate 70% sensitivity for detection of Pneumocystis jiroveci in human immunodeficiency virus (HIV) patients. Bronchoalveolar lavage sampling has greater than 90% sensitivity but is a far more invasive procedure. Therefore, bronchoalveolar lavage testing is often recommended as a follow-up after a negative induced sputum. In HIV-negative patients, the utility of induced sputum testing is still not well defined. OBJECTIVE To determine whether repeat induced sputum sampling increases diagnostic yield and might thereby reduce the need for follow-up bronchoalveolar lavage sampling. To determine the utility of induced sputum sampling in HIV-negative patients. DESIGN A 2-year retrospective review of the utility of repeat induced sputa testing in patients with previous first and/or second negative induced sputa. Retrospective review of induced sputa detection in HIV-negative patients. RESULTS Repeat testing of induced sputa for Pneumocystic jirovecii did not significantly increase diagnostic yield. Furthermore, in HIV-negative patients, induced sputum testing was diagnostically insensitive. CONCLUSIONS Bronchoalveolar lavage testing should be performed initially in HIV-negative patients and after a first negative induced sputum in HIV-positive patients.

Effective Use of PCR for the Detection of Cytomegalovirus Viremia and Monitoring Therapy in Immunocompromised Patients

Objective: To establish criteria for the most productive use of quantitative cytomegalovirus (CMV) polymerase chain reaction (PCR) in transplant and HIV patients, both for diagnosis and monitoring infections. Method: We evaluated the medical records of 108 HIV, bone marrow transplant (BMT), and solid organ transplant (SOT) patients who had positive CMV viral load tests. Results: Cytomegalovirus was detected at median of 47 and 183.5 days after BMT and SOT, respectively. All HIV patients who had positive CMV viremia had CD4 cell counts <175 cells/μL, and all HIV patients with endorgan disease had CD4 cell counts <75 cells/ μL. The median time for CMV to become undetectable after treatment was 22, 21, and 31 days for HIV, BMT, and SOT patients, respectively. Conclusion: Cytomegalovirus viral load screening focusing on high-risk periods may be cost effective. A CMV viral load does not decrease rapidly with treatment. The CMV PCR for monitoring therapy should not be performed more than once a week.

Limited Utility of Bone Marrow Culture: A Ten-Year Retrospective Analysis

Background A retrospective examination of the utility of bone marrow sampling for identification of microorganisms was performed in an urban tertiary care hospital. Methods A retrospective review of culture and histology data from bone marrow specimens was performed for a 10-year period. Results Neither bone marrow culture nor special stains for microorganisms provided incremental benefit in identifying microbial agents compared with other methods such as blood culture. Conclusion Bone marrow aspiration/biopsy should only be performed selectively for diagnosis of an infectious etiology.

Rapid Identification of Staphylococcus aureus Directly from Bactec Blood Culture Broth by the BinaxNOW S. aureus Test

ABSTRACT The BinaxNOW Staphylococcus aureus testing showed sensitivity, specificity, and positive and negative predicative values of 97.6%, 100%, 100%, and 98.4%, respectively, for identification of S. aureus from Bactec blood culture broth. Importantly, the test performed equally well on aerobic and anaerobic culture broth.