Antimicrobial Resistance of Human Campylobacter Species Infections in Saskatchewan, Canada (1999-2006): A Historical Provincial Collection of All Reported Cases

To describe a historical baseline of antimicrobial resistance (AMR) profiles for human clinical Campylobacter species isolates obtained by laboratory surveillance in the province of Saskatchewan from 1999 to 2006; to determine if there were differences in resistance between Campylobacter jejuni and Campylobacter coli; and to determine if there were changes in the annual resistance levels in the two species. One thousand three hundred seventy-eight Campylobacter isolates were subjected to antimicrobial susceptibility testing using the E-test method. Annual resistance levels in C. jejuni and C. coli were compared using logistic regression models. One thousand two hundred (87.1%) isolates were C. jejuni and 129 (9.4%) were C. coli. Resistance in C. jejuni isolates included ciprofloxacin (CIP: 9.4%), erythromycin (ERY: 0.5%), and tetracycline (33.3%). CIP resistance in C. jejuni was higher in 1999 (15.5%, odds ratio [OR] = 3.96, p = 0.01), 2000 (12.7%, OR = 3.10, p = 0.01), 2005 (10.2%, OR = 2.47, p = 0.05), and 2006 (13.0%, OR = 3.22, p = 0.01) compared with 2004 (4.4%). C. coli had significantly higher CIP resistance (15.5%, OR = 1.78, p = 0.03), ERY resistance (13.2%, OR = 60.12, p < 0.01), multidrug resistance (2.3%, OR = 36.29, p < 0.01), and CIP-ERY resistance (3.1%, OR = 50.23, p < 0.01) compared with C. jejuni. This represents the first and most current report of AMR of the collective human Campylobacter isolates from a province in Canada and provides a baseline against which current and future resistance patterns can be compared. Fluoroquinolone resistance in C. jejuni isolates fluctuated from 1999 to 2006, including an increased prevalence in 2005-2006, while macrolide/lincosamide resistance remained very low. Human clinical C. jejuni isolates from Saskatchewan demonstrated resistance to multiple antimicrobials but had significantly less fluoroquinolone and macrolide resistance than C. coli isolates.

HIV misdiagnosis: A root cause analysis leading to improvements in HIV diagnosis and patient care

BACKGROUND

Standard diagnostic testing for HIV infection has traditionally relied on a high sensitivity HIV antibody screening test using an enzyme-linked immunosorbent assay (ELISA) followed by a high specificity antibody confirmatory test such as a Western Blot. Recently several of the screening assays have been enhanced with an ability to identify p24 antigen thereby narrowing the diagnostic window.

OBJECTIVES

To explore the implications of enhanced HIV screening methods that may be leading to HIV misdiagnoses.

STUDY DESIGN

A patient deemed to be an HIV infected 'elite controller' was found to be misdiagnosed when undergoing detailed investigations prior to initiating antiretroviral therapy. A root cause analysis was performed to identify the causative factors of this misdiagnosis. A retrospective review of all "elite controllers" in Alberta, Canada revealed challenges of current HIV testing algorithms.

RESULTS

Technical and human factors were identified as being causative in this HIV misdiagnosis including (i) high rates of false reactive results on the Abbott ARCHITECT HIV-1&2 COMBO EIA, (ii) human error in reading the initial Western blot, (iii) HIV algorithmic directives in which confirmatory (Western blot) testing was not performed on a repeatedly reactive screen test. The outcome of this analysis identified opportunities for improvement, including implementation of a newly approved (automated) confirmatory assay and improved communication between the clinician and laboratory.

CONCLUSIONS

HIV testing remains problematic despite significant advances in HIV test performance and algorithm development, presenting new and unexpected issues. Ensuring a high-quality management system including implementation of the latest HIV technologies and algorithms along with human resources and policies are required to minimize the impact of false positive diagnoses, especially in the era of universal screening and 'test and treat' recommendations.

Unique combined penA/mtrR/porB mutations and NG-MAST strain types associated with ceftriaxone and cefixime MIC increases in a 'susceptible' Neisseria gonorrhoeae population

OBJECTIVES

To determine which mutations in penA, mtrR and porB are implicated in increasing minimum MICs of ceftriaxone and cefixime in a susceptible gonococcal population and to ascertain associations with gonococcal strain types (STs).

METHODS

One hundred and forty-six Neisseria gonorrhoeae isolates formed two extended-spectrum cephalosporin susceptibility groups: group 1 isolates with cefixime and ceftriaxone MICs of 0.0005-0.016 mg/L; and group 2 isolates with cefixime MICs of 0.03-0.125 mg/L (n = 24) and ceftriaxone MICs of 0.03-0.06 mg/L (n = 23). Mutation patterns in penicillin-binding protein 2 (PBP2; penA), multiple transfer resistance repressor (MtrR; mtrR) and porin B (PorB; porB) were ascertained by DNA sequence and bioinformatic analysis. STs were determined using N. gonorrhoeae multiantigen sequence typing (NG-MAST).

RESULTS

Most isolates carried PBP2 mutation pattern IX (D345a, F504L, A510V, A516G and P551L; 50/146, 34.2%), a G45D substitution in MtrR (37.7%) and a wild-type (WT) sequence for PorB (43.2%). Group 2 gonococcal isolates were significantly associated with: penA pattern IX; dual mutations in the promoter (A-) and DNA dimerization domain (H105Y) of MtrR; and G120K;A121D substitutions in PorB. There were 50 combined penA/mtrR/porB mutation patterns, with corresponding patterns I/WT/WT and IX/G45D/G120K;A121D predominating. Gonococci susceptible to ceftriaxone and cefixime were significantly associated with NG-MAST ST 25 (33/36; 92%) and the combined penA/mtrR/porB mutation pattern I/WT/WT. No combined mutation pattern or specific ST was associated with elevated ceftriaxone MICs. NG-MAST ST 3654 was significantly associated with the pattern IX/G45D/G120K;A121D and cefixime group 2 isolates.

CONCLUSIONS

Specific single or combined mutation patterns in penA, mtrR and porB and specific STs were associated with differences in susceptibility to ceftriaxone and cefixime.

Longitudinal analysis of the evolution and dissemination of Neisseria gonorrhoeae strains (Saskatchewan, Canada, 2005 to 2008) reveals three major circulating strains and convergent evolution of ciprofloxacin and azithromycin resistance

A longitudinal study combining multilocus sequence typing with molecular evolutionary analysis determined the distribution, population structure, and evolution of antibiotic resistance in Neisseria gonorrhoeae isolates in Saskatchewan that were collected between 2005 and 2008. Of 195 gonococcal isolates examined, 29 sequence types (STs) were identified with 3 major circulating strains (ST-1 through ST-3) comprising 52% of all gonococcal isolates studied. The prevalences, persistence, distribution patterns, and clonalities of these isolates strongly suggest that gonorrhea endemicity within this broad geographic region was driven by these 3 circulating strains. ST-1 exhibited a significantly (P = 0.001) higher prevalence throughout the study than did the others, accounting for ∼25% of the tested isolates each year. The spatial distributions of the gonococcal strains indicated that ST-1 in 2007 entered a linear component of the sexual network, reaching the remote north and resulting in the further spread and maintenance of infection. Ciprofloxacin and azithromycin resistances were observed in distantly related gonococcal lineages, clearly indicating the convergent acquisition of these antibiotic-resistant phenotypes. In addition, all ciprofloxacin- and azithromycin-resistant lineages were found at the edges of the minimum spanning tree, far from the major lineages, suggesting that these antibiotic phenotypes were most likely introduced into the province. In contrast, resistance to penicillin was found mostly in the endemic gonococcal lineages, suggesting that penicillin resistance was probably acquired in Saskatchewan as a result of spontaneous mutations in already-established lineages. Tetracycline resistance was present in all STs except one, indicating its ubiquitous nature in the gonococcal population studied.

Epidemic of invasive pneumococcal disease, western Canada, 2005-2009

In Canada before 2005, large outbreaks of pneumococcal disease, including invasive pneumococcal disease caused by serotype 5, were rare. Since then, an epidemic of serotype 5 invasive pneumococcal disease was reported: 52 cases during 2005, 393 during 2006, 457 during 2007, 104 during 2008, and 42 during in 2009. Of these 1,048 cases, 1,043 (99.5%) occurred in the western provinces of Canada. Median patient age was 41 years, and most (659 [59.3%]) patients were male. Most frequently representing serotype 5 cases (compared with a subset of persons with non-serotype 5 cases) were persons who were of First Nations heritage or homeless. Restriction fragment-length polymorphism typing indicated that the epidemic was caused by a single clone, which multilocus sequence typing identified as sequence type 289. Large pneumococcal epidemics might go unrecognized without surveillance programs to document fluctuations in serotype prevalence.

Influence of conserved and hypervariable genetic markers on genotyping circulating strains of Neisseria gonorrhoeae

Presently there is no vaccine against Neisseria gonorrhoeae and therefore accurate information on gonococcal transmission plays a crucial role for interventions designed to limit the spread of infections caused by this microorganism. We evaluated the impact of two different categories of genetic markers, (i) concatenated sequences of 10 housekeeping genes and (ii) hypervariable porB DNA sequences, on the genetic relatedness and subsequently on genotyping analysis of this human pathogen. Eighty gonococcal isolates from Canada, China, the US, Argentina, Venezuela and Chile, collected over different times, were analyzed. Our results show that the choice of genetic marker had a profound effect on the interpretation of genotyping results associated with N. gonorrhoeae. The concatenated sequences of the housekeeping genes preserved the genetic relatedness of closely related isolates, enabling detection of the predominant strains circulating within a community (Saskatchewan, Canada) over an extended period of time. In contrast, a genetic marker based on antigen gene, porB, may lead to a failure to detect these predominant circulating strains. Based on the analysis of the DNA sequences of the 10 housekeeping genes, we identified two major clonal complexes, CC33 and CC22, which comprised STs from China, and Argentina as well as two STs from Canada. Several minor clonal complexes were observed among isolates from Saskatchewan. eBURST analysis suggested that the majority of the tested gonococcal isolates from Saskatchewan, Canada were endemic, with only a couple of genotypes introduced.

Human infection with a triple-reassortant swine influenza A(H1N1) virus containing the hemagglutinin and neuraminidase genes of seasonal influenza virus

A reassortant influenza A(H1N1) virus of swine origin distinct from the pandemic H1N1 2009 strain was isolated from 3 patients, all of whom worked at the same large hog operation in Saskatchewan, Canada. The genomic composition of the isolates has not been previously reported, to our knowledge, and was the product of a genetic reassortment between seasonal H1N1 and triple-reassortant influenza virus that emerged in North American swine during the late 1990s. The neuraminidase and hemagglutinin genes of A/Saskatchewan/5350/2009, A/Saskatchewan/5351/2009, and A/Saskatchewan/5131/2009 were derived from human H1N1 virus and were closely related to those of A/Brisbane/59/2007.

Ceftiofur resistance in Salmonella enterica serovar Heidelberg from chicken meat and humans, Canada

Use of this drug in chickens may limit effectiveness of cephalosporins in treating human infections.

The Canadian Integrated Program for Antimicrobial Resistance Surveillance describes a strong correlation (r = 0.9, p<0.0001) between ceftiofur-resistant Salmonella enterica serovar Heidelberg isolated from retail chicken and incidence of ceftiofur-resistant Salmonella serovar Heidelberg infections in humans across Canada. In Québec, changes of ceftiofur resistance in chicken Salmonella Heidelberg and Escherichia coli isolates appear related to changing levels of ceftiofur use in hatcheries during the study period, from highest to lowest levels before and after a voluntary withdrawal, to increasing levels after reintroduction of use (62% to 7% to 20%, and 34% to 6% to 19%, respectively). These events provide evidence that ceftiofur use in chickens results in extended-spectrum cephalosporin resistance in bacteria from chicken and humans. To ensure the continued effectiveness of extended-spectrum cephalosporins for treating serious infections in humans, multidisciplinary efforts are needed to scrutinize and, where appropriate, limit use of ceftiofur in chicken production in Canada.

Human papillomavirus typing and viral gene expression analysis for the triage of women with abnormal results from papanicolaou test smears to colposcopy

CONTEXT

A cascade of molecular tests for human papillomavirus (HPV), as a follow-up to Papanicolaou test screening, could eliminate unnecessary colposcopy. Tests based on detection of HPV E6 messenger RNA (mRNA) are already being used as screening tools, but there is a good biological rationale for expecting that an increase in the relative amounts of HPV E6 mRNA in cervical samples may better predict cancerous transformation.

OBJECTIVE

To compare some of the available diagnostic methods and our novel method of relative quantification (RQ) of HPV gene expression for the effective triage of women with abnormal results from Papanicolaou tests to colposcopy.

DESIGN

Sensitivities, specificities, and likelihood ratios were calculated for repeat Papanicolaou test smears, HPV DNA polymerase chain reactions, HPV genotyping, HPV-16 E6 mRNA detection, and the RQ of HPV-16 E6 mRNA calibrated to cellular RNA and DNA levels and standardized to viral load.

RESULTS

Human papillomavirus genotype in combination with a repeat Papanicolaou test can be used to categorize most women (96%) with cervical intraepithelial neoplasia of grade 2 or higher for colposcopy while eliminating 44% of women with cervical intraepithelial neoplasia 1 or less. The presence of HPV-16 E6 mRNA (P < .001) and RQ of HPV-16 E6 mRNA (P < .001) displayed significant median differences among the various grades of cervical intraepithelial neoplasia. Further testing of women who are positive for HPV-16 demonstrated that the RQ of E6 mRNA has diagnostic potential when combined with Papanicolaou testing in populations with higher disease prevalence.

CONCLUSIONS

The RQ of HPV E6 mRNA and HPV genotype could be useful in a cascade of diagnostic testing designed to refer women with findings of cervical abnormalities for colposcopy or treatment while reducing triage numbers.

The impact of the distribution of human papillomavirus types and associated high-risk lesions in a colposcopy population for monitoring vaccine efficacy

CONTEXT

Impact studies of the new human papillomavirus (HPV) vaccines will be biased unless local baseline distribution studies are conducted. Vaccine cross protection for other important oncogenic HPV types and the emergence of potential genotype replacements require the knowledge of the prevaccine epidemiology of HPV.

OBJECTIVE

To determine the prevaccine distribution of HPV types in Saskatchewan, using a subpopulation of women referred to a colposcopy clinic.

DESIGN

One thousand three hundred fifty-five specimens obtained during colposcopic examination were typed for HPV using L1 or E1 gene polymerase chain reaction and direct sequencing. HPV-16 and HPV-31 infections were confirmed with real-time E6 polymerase chain reaction. Indeterminate samples were analyzed using Luminex technology. Correlations of the HPV type and histology were examined for statistical significance.

RESULTS

The most commonly identified genotype in patients with cervical intraepithelial neoplasia grade 2 or worse was HPV-16 (46.7%) followed by HPV-31 (14.7%) and then HPV-18 (3.9%). Fifteen of 330 specimens that were positive for HPV-16 or HPV-31 were further resolved to be mixed HPV-16/HPV-31 infections by real-time polymerase chain reaction. The risk of cervical intraepithelial neoplasia associated with HPV-18 infection (0.4-1.7) is substantially lower than with either HPV-16 (3.6-11.0) or HPV-31 (1.8-12.6).

CONCLUSIONS

HPV-31 is contributing significantly to the proportion of women with cervical intraepithelial neoplasia in our population and shows a higher prevalence than HPV-18 in high-grade lesions. The clinical significance of HPV-31 may be underestimated and its continued significance will depend on the level of cross protection offered by the new vaccines.

Rapid detection of Norovirus based on an automated extraction protocol and a real-time multiplexed single-step RT-PCR

BACKGROUND

Molecular diagnosis of Norovirus infection can be a complex multistep process, which requires significant user intervention and expertise, and is not amenable to automation without extensive validation and optimization.

OBJECTIVES

To develop a real-time multiplexed RT-PCR assay with automated sample preparation that requires only a single-step and a single-tube for reverse transcription, amplification, and detection while exceeding the sensitivity of conventional PCR for broad-spectrum Norovirus detection.

STUDY DESIGN

Limit of detection was assessed against dilutions of clinical specimens. Fifty archived extractions were used to compare TaqMan sensitivity with either a separate RT using random primers or a single-step RT-PCR. The sensitivity of the novel assay was compared with conventional RT-PCR using 100 specimens from gastroenteritis cases.

RESULTS

Automated extraction reduced RNA recovery by 0.5 logs compared to manual extraction but was more effective at removing PCR inhibitors from stool specimens. The optimized single-step real-time RT-PCR demonstrated no reduction in sensitivity. Together, the sensitivity of the novel assay was 19% higher than manual extraction with conventional RT-PCR.

CONCLUSIONS

A semi-automated and simplified molecular diagnostic protocol for the rapid detection of Norovirus has been achieved. PCR inhibitors are present in human fecal specimens and cause a significant problem for Norovirus detection by RT-PCR.

Use of immunoglobulin G avidity assays for differentiation of primary from previous infections with West Nile virus

Since its introduction in 1999, West Nile virus (WNV) infections have spread rapidly across the North American continent. Diagnosis of acute WNV infection by detection of WNV-specific immunoglobulin M (IgM) is complicated by the persistence of detectable IgM for more than 1 year in some patients. IgG antibody avidity testing was assessed as a supplemental assay in the diagnosis of current infections. Three groups of serum samples were assayed in parallel by two different IgG avidity test systems (indirect immunofluorescence test [IIFT] and prototype enzyme-linked immunosorbent assay [ELISA]; EUROIMMUN, Luebeck, Germany). Group I (40 sera taken between 2 and 9 days after the onset of influenza-like symptoms) and group II (40 sera taken between 10 and 43 days after onset) were acute and convalescent specimens from patients with a positive anti-WNV IgM test (ELISA; Focus Diagnostics, Cypress, CA). Group III consisted of 43 patient sera collected between 6 and 12 months after infection. IgG antibodies specific for WNV were detected in 38% (ELISA) and 50% (IIFT) of group I sera, in 90% (ELISA and IIFT) of group II sera, and in 100% (ELISA and IIFT) of group III sera. Low-avidity IgG antibodies were demonstrated in 86% (ELISA) and 95% (IIFT) of IgG-positive patient samples taken between 2 and 43 days after the onset of symptoms (groups I and II). High-avidity IgG antibodies were detected in 100% of group III sera obtained 6 months or more after the onset of symptoms (ELISA and IIFT). IgG avidity tests for WNV infections are rapid and simple to perform. The determination of IgG avidity provides additional diagnostic certainty in differentiating between recently acquired and previous infections with WNV.

Development of a triplex real-time PCR assay for detection of Panton-Valentine leukocidin toxin genes in clinical isolates of methicillin-resistant Staphylococcus aureus

Community-associated methicillin-resistant Staphylococcus aureus harboring Panton-Valentine leukocidin (PVL) genes is an emerging pathogen. A novel real-time PCR assay for identification of MRSA isolates containing PVL was developed. The PVL assay was used in a triplex format allowing simultaneous amplification of mecA, nuc, and PVL genes in 614 clinical isolates. This assay facilitates the rapid identification of PVL-positive isolates of MRSA.

Rapid genotyping of hepatitis C virus by primer-specific extension analysis

Quick and accurate genotyping of hepatitis C virus (HCV) is becoming increasingly important for clinical management of chronic infection and as an epidemiological marker. Furthermore, the incidence of HCV infection with mixed genotypes has clinical significance that is not addressed by most genotyping methods. We have developed a fluorescence-based genotyping assay called primer-specific extension analysis (PSEA) for the most prevalent HCV genotypes and have demonstrated the capacity of PSEA-HCV for detecting mixed-genotype HCV infections. PSEA-HCV detects genotype-specific sequence differences in the 5' untranslated region of HCV in products amplified by the COBAS AMPLICOR HCV Test, v2.0. Simulated mixed HCV infection of plasma with RNase-resistant RNA controls demonstrates that PSEA-HCV can detect as many as five genotypes in one specimen. Furthermore, in dual-genotype simulations, PSEA-HCV can unequivocally detect both genotypes, with one genotype representing only 3.1% of the mixture (313/10,000 IU in starting plasma). Compared to INNO-LiPA HCV II, both assays determined the same genotype for 191/199 (96%) patient specimens (175 subtype and 16 genotype-only identifications). Following the initial evaluation, PSEA-HCV was used routinely to genotype HCV from patient specimens submitted to our laboratory (n=312). Seventeen (5.4%) mixed infections were identified. The distribution of single-infection HCV genotypes in our population was 60.9% type 1 (n=190), 12.8% type 2 (n=40), 20.2% type 3 (n=63), 0.3% type 4 (n=1), and 0.3% other (n=1). In conclusion, PSEA-HCV provides an inexpensive, high-throughput screening tool for rapid genotyping of HCV while reliably identifying mixed HCV infections.

High-throughput qualitative multiplex 5' nuclease assay using post-only PCR analysis

Homogenous fluorescence PCR assays offer distinct advantages for qualitative testing and are gaining immense popularity in fields like diagnostic microbiology. To meet the demand of high-volume laboratories, we developed a protocol for qualitative multiplex 5' nuclease assays using post-only PCR analysis. This novel approach overcomes throughput problems encountered with the established methods for TaqMan detection on the ABI PRISM 7700 Sequence Detection system and permits off-site TaqMan PCR, which can be analyzed several days after the reactions are completed. We have validated this novel protocol using an assay for the identification of Bordetella pertussis against real-time and plate-read analysis methods and have shown that our proposed protocol produces no difference in qualitative calls.

The use of TaqMan PCR assay for detection of Bordetella pertussis infection from clinical specimens

OBJECTIVE

The routine clinical laboratory detection of Bordetella pertussis is through culture, which can require 5 to 7 days for the bacteria to grow. Using a polymerase chain reaction (PCR) assay can shorten this detection time while increasing the sensitivity of detection with similar specificity. This study compared culture with TaqMan PCR for detection of B pertussis in clinical specimens and the turnaround time for each assay during the pertussis season.

MATERIALS AND METHODS

Nasopharyngeal swabs in Regan-Lowe transport media were collected from 1556 persons who had symptoms of whooping cough or who had had contact with infected persons; the swabs were submitted for B pertussis detection during the pertussis season. A single nasopharyngeal swab from each patient was submitted for both culture and TaqMan PCR detection. Upon receipt of the specimens, the swabs were inoculated onto Regan-Lowe agar for culture and incubated for up to 7 days. The same swab was processed for PCR detection using TaqMan PCR assay. A second nested PCR was used on positive specimens for resolution purposes. The TaqMan PCR assay was performed 3 to 5 days a week, whereas the culture was performed 6 days a week. All specimens were processed on the same day or earliest possible working day for TaqMan or culture, and specimens queued for resolution by nested PCR were batched.

RESULTS

There were a total of 275 PCR positives and 28 culture positives. After resolution with the second nested PCR, the sensitivity, specificity, positive predictive value, and negative predictive value were 100%, 97.4%, 87.6%, and 100% for TaqMan PCR and 11.6%, 100%, 100%, and 85.7% for culture. The average turnaround time for positive culture was 5.1 days, and the average turnaround time for PCR was 2.3 days.

CONCLUSION

The TaqMan PCR assay has superior sensitivity and shorter turnaround time over culture because it can be finished within one working day. Furthermore, the same swab can be used for culture of the bacteria for antibiotic susceptibility testing. The early detection of pertussis using TaqMan PCR assay allows early intervention on the spread of the disease and the ability to culture the bacteria from the same swab, thereby eliminating the need for a second swab and allowing for detection of antibiotic resistance.

Comparison of Chemicon SimulFluor direct fluorescent antibody staining with cell culture and shell vial direct immunoperoxidase staining for detection of herpes simplex virus and with cytospin direct immunofluorescence staining for detection of varicella-zoster virus

A new rapid direct immunofluorescence assay, the SimulFluor direct fluorescent-antibody (DFA) assay, which can simultaneously detect herpes simplex virus types 1 and 2 (HSV-1 and -2) and varicella-zoster virus (VZV), was evaluated in comparison with our current standard procedures of (i) shell vial direct immunoperoxidase (shell vial IP) staining and cell culture for detection of HSV and (ii) cytospin DFA staining for VZV detection. A total of 517 vesicular, oral, genital, and skin lesion specimens were tested by all three procedures. For HSV detection, the SimulFluor DFA assay had an overall sensitivity, specificity, positive predictive value, and negative predictive value of 80.0, 98.3, 92.3, and 95.1%, respectively, when compared to culture. Shell vial IP staining had a sensitivity, specificity, positive predictive value, and negative predictive value of 87.6, 100, 100, and 96.9%, respectively, when compared with cell culture. The SimulFluor DFA assay, however, offers same-day, 1.5-hours results versus a 1- to 2-day wait for shell vial IP staining results and a 1- to 6-day wait for culture results for HSV. For VZV detection SimulFluor DFA staining detected 27 positive specimens as compared to 31 by our standard cytospin DFA technique--a correlation of 87.1%. A positive SimulFluor reaction for VZV is indicated by yellow-gold fluorescence compared to the bright apple-green fluorescence observed by cytospin DFA staining. There is no difference in turnaround time between the two assays. The SimulFluor DFA assay is a rapid immunofluorescence assay that can detect 80% of the HSV-positive specimens and 87% of the VZV-positive specimens with a 1.5-h turnaround time.

Performance characteristics of the Becton Dickinson ProbeTec System for direct detection of Chlamydia trachomatis and Neisseria gonorrhoeae in male and female urine specimens in comparison with the Roche Cobas System

OBJECTIVE

The Becton Dickinson BDProbeTec ET System is a new semiautomated system using strand displacement amplification technology that simultaneously amplifies and detects Chlamydia trachomatis and Neisseria gonorrhoeae DNA. The strand displacement amplification products are hybridized with a fluorescent detector probe and are captured by a chemiluminescent assay in a microwell format. An amplification control is also included to monitor assay inhibition. This study evaluated the performance of the BDProbTec ET system in detecting C trachomatis and N gonorrhoeae in male and female urine specimens, calculated its ability to process large volumes of specimens, and determined the inhibition rate.

MATERIALS AND METHODS

Eight hundred twenty-five male and 399 female urine specimens were tested for both C trachomatis and N gonorrhoeae with the BDProbeTec ET system, and results were compared with those of the Roche Amplicor Cobas system. All urine specimens were processed on both assays on the same day they were received, according to the manufacturers' instructions. Discrepant results were resolved by in-house polymerase chain reaction assays. Internal or amplification controls were also used in each specimen assay to monitor inhibition. The throughput of the BDProbTec ET system was further tested with 150 urine specimens on an 8-hour shift for 2 days.

RESULTS

The overall sensitivity, specificity, positive predicative value, and negative predicative value for for detection of chlamydia were 95.3%, 99.3%, 95.9%, and 99.2% for strand displacement amplification and 95.9%, 98.3%, 90.6%, and 99.3% for the Roche Amplicor system. For detection of gonorrhea, these values were 100%, 99.7%, 88.2%, and 100% and 96.7%, 98.9%, 69%, and 99.9%, respectively. The overall inhibition rates for both strand displacement amplification and Roche Amplicor were less than 3.5%. The BDProbTec ET system was able to produce 150 results each for chlamydia and gonorrhea and the internal control within the 8-hour shift.

CONCLUSIONS

The performance characteristics of the BDProbeTec ET assay are similar to those of the Roche Amplicor polymerase chain reaction for detection of chlamydia and gonorrhea in male and female urine specimens. The system was able to produce 300 results in an 8-hour shift.

Comparison of the effectiveness of polymerase chain reaction and enzyme immunoassay in detecting Chlamydia trachomatis in different female genitourinary specimens

BACKGROUND

In high-volume laboratories, enzyme immunoassay (EIA) is the most commonly used method of detecting Chlamydia trachomatis. The optimal specimen for detecting C trachomatis is a combined urethral and cervical swab.

OBJECTIVE

To compare EIA with the combined urethral and cervical swab with polymerase chain reaction (PCR) on urine alone and urine mixed with cervical cells.

PATIENTS AND METHODS

Phase 1 of the study included 752 sets of specimens used for comparison. In phase 2, another 212 samples of urine and urine plus cervical cells were added to the study for comparison of the 2 specimen types using PCR.

RESULTS

In phase 1, 648 samples were negative and 76 were positive by all 3 methods and specimen combinations. Enzyme immunoassay was able to detect 81 positive samples (10.8%), whereas PCR on urine alone detected 97 positive samples (12.9%) and PCR on urine plus cervical cells detected 102 positive samples (13.6%), giving a sensitivity of 75%, 93.3%, and 98. 1% respectively. In phase 2, PCR on urine alone detected 119 positive samples (12.3%) and PCR on urine plus cervical cells detected 127 positive samples (13.1%), with a sensitivity of 92.2% and 98.5%, respectively.

CONCLUSION

Polymerase chain reaction on urine alone or urine plus cervical cells is superior to EIA on combined cervical and urethral swabs. There is a slight advantage of adding cervical cells to the urine compared with the urine specimen alone when PCR is used as the assay for detection. The total inhibition rate in our female population is only 3.1% when PCR is used.

Minimal inhibitory effect of male urine on detection of Chlamydia trachomatis by Roche Amplicor PCR

A total of 1120 specimens of fresh urine from male patients was tested for Chlamydia trachomatis with the Roche Amplicor PCR Kit and an in-house PCR assay. The in-house PCR had an internal control to monitor inhibitory effects of clinical specimens on the PCR assay. All urine samples were processed within 24-48 h of collection and DNA was extracted on the same day that the assays were performed. Specimens that gave discrepant PCR results were tested by a reference laboratory with both the Roche Amplicor kit and their in-house PCR assay. Of the 1120 samples, 174 gave positive results in both assays and 942 gave negative results in both assays. Only one specimen showed an inhibitory effect on the in-house PCR assays, as indicated by failure to produce the internal control PCR product. This specimen gave negative results by both assays. There were four discrepant results in the two PCR assays. One was a false negative result obtained with the Roche Amplicor kit and the remaining three discrepant results could not be resolved because there was an insufficient quantity of specimen. This study demonstrated that the Roche Amplicor kit could effectively detect C. trachomatis in urine specimens from this population of male patients with negligible inhibition of PCR.

Comparison of four latex kits for detection of E. coli O157

OBJECTIVE

To compare four Escherichia coli O157 test kits for detection of E. coli O157:H7 isolated from clinical specimens.

DESIGN

One hundred two Escherichia coli O157:H7 isolates obtained from stored specimens and 99 non-sorbitol fermenting enterobacteriaceae isolates from current clinical specimens were tested against four latex kits: Wellcolex, RIM, Prolex, and Oxoid. Each isolate was tested against all four kits on the same day.

SETTING

Provincial Laboratory of Saskatchewan, Canada.

PATIENTS

Patients from Saskatchewan with diarrhea submitted stool specimens through their family physicians to the Provincial Laboratory for detection of enteric pathogens including E. coli O157:H7.

RESULTS

The sensitivity and specificity of each test kit were: Wellcolex 100%, 99%; RIM 100%, 99%; Prolex 99%, 100%; Oxoid 100%, 100%. The Prolex kit failed to detect one E. coli O157:H7 isolate.

CONCLUSION

All kits tested were able to identify E. coli O157 isolated from stool specimens. Further study with Prolex is needed to assess the significance of the one missed E. coli O157 isolate.

A comparison of the Genie and western blot assays in confirmatory testing for HIV-1 antibody

The Genie HIV-1/2 kit (Sanofi Diagnostics Pasteur, Montreal, Quebec), a synthetic-peptide solid-phase enzyme immunoassay, was evaluated as a confirmatory assay for HIV-1 antibodies in comparison with Western blot (BioRad, Hercules, CA, USA) on 50 stored HIV-1 antibody-positive sera and the 137 sera yielding repeated positive results in the conventional EIA screen out of 13405 fresh patient sera from Saskatchewan in 1993. The stored HIV-1-positive sera were uniformly positive in the Genie test. Of the 137 EIA screen-positive sera, 33 were uniformly positive and 64 were uniformly negative in Genie and Western blot; 36 were Genie-negative and indeterminate by Western blot; and four were Genie indeterminate, of which one was negative and three were indeterminate by Western blot. All HIV-1 Western blot-indeterminate and Genie-interdeterminate sera were negative in radio-immunoprecipitation assay (RIPA) and Western blot for HIV-1 and HIV-2 antibodies performed by a reference laboratory. Genie gave an accurate definitive result for 97% of EIA positive sera compared with 71% for Western blot. There was excellent correlation between Genie, Western blot and RIPA results. However, the Genie assay was faster, less costly and yielded fewer indeterminate results than Western blot in confirmatory testing for HIV-1 antibodies.

The use of a confirmatory assay to increase the sensitivity and specificity of the Chlamydiazyme test

The blocking assay was used to reexamine 15,662 patient specimens (2,565 male specimens, 13,097 female specimens) that were submitted for Chlamydia detection using the Chlamydiazyme EIA assay (Abbott Laboratories, North Chicago, IL). Specimens that gave optical density (OD) readings between 1.99 to cutoff and between cutoff to 3 times the negative control in the Chlamydiazyme EIA assay were analyzed further by the blocking assay during the phase 1 study. In the phase 2 study, another 1,120 specimens (473 male specimens and 647 female specimens) that had the above mentioned OD range in the Chlamydiazyme assay were tested with the blocking assay and the direct fluorescent antibody test using the cytospin method. Significant finding from phase 1 study demonstrated that 42.3% of the male specimens with optical density between cutoff to three times the negative control can be blocked by blocking assay (confirmed positive), whereas only 50% of the female specimens with OD range between cutoff to .5 were blocked by the blocking assay. In the phase 2 study, similar results were obtained with the blocking assay. The direct fluorescent antibody test showed excellent correlation with the blocking assay. These data showed that both blocking or direct fluorescent antibody tests can be used for confirmation purposes to increase the sensitivity and specificity of the assay. However, for specimens with OD values below the cutoff to 3 times the negative control, it was necessary to reassess the specimens by either of the methods. This was true especially with the male specimens.

A 1-year evaluation of Syva MicroTrak Chlamydia enzyme immunoassay with selective confirmation by direct fluorescent-antibody assay in a high-volume laboratory

TThe Syva MicroTrak Chlamydia enzyme immunoassay (EIA; Syva Company, San Jose, Calif.) with cytospin and direct fluorescent-antibody assay (DFA) confirmation was evaluated on 43,630 urogenital specimens over a 1-year period in the Provincial Laboratory in Regina, Saskatchewan, Canada. This was a two-phase study intended to define a testing algorithm for Chlamydia trachomatis that would be both highly accurate and cost-effective in our high-volume (> 3,000 tests per month) laboratory. The prevalence of C. trachomatis infection in our population is moderate (8 to 9%). In phase 1, we tested 6,022 male and female urogenital specimens by EIA. All specimens with optical densities above the cutoff value and those within 30% below the cutoff value were retested by DFA. This was 648 specimens (10.8% of the total). A total of 100% (211 of 211) of the specimens with optical densities equal to or greater than 1.00 absorbance unit (AU) above the cutoff value, 98.2% (175 of 178) of the specimens with optical densities of between 0.500 and 0.999 AU above the cutoff value, and 83% (167 of 201) of the specimens with optical densities within 0.499 AU above the cutoff value were confirmed to be positive. A total of 12% (7 of 58) of the specimens with optical densities within 30% below the cutoff value were positive by DFA. In phase 2, we tested 37,608 specimens (32,495 from females; 5,113 from males) by EIA. Only those specimens with optical densities of between 0.499 AU above and 30% below the cutoff value required confirmation on the basis of data from phase 1 of the study. This was 4.5% of all specimens tested. This decrease in the proportion of specimens requiring confirmation provides a significant cost savings to the laboratory. The testing algorithm gives us a 1-day turnaround time to the final confirmed test results. The MicroTrak EIA performed very well in both phases of the study, with a sensitivity, specificity, positive predictive value, and negative predictive value of 96.1, 99.1, 90.3, and 99.7%, respectively, in phase 2. We suggest that for laboratories that use EIA for Chlamydia testing, a study such as this one will identify an appropriate optical density range for confirmatory testing for samples from that particular population.

Comparison of agar disk diffusion, microdilution broth, and agar dilution for testing antimicrobial susceptibility of coagulase-negative staphylococci

A collection of 120 oxacillin-susceptible and 120 oxacillin-resistant coagulase-negative staphylococci (CNS) from six tertiary care hospital laboratories were tested by agar disk diffusion, three microdilution broth systems (Sensititre, Dynatech, and Alpkem), and the Vitek AutoMicrobic system for comparison with reference agar dilution results. The antimicrobial agents tested were oxacillin, cefazolin, cefotaxime, cefuroxime, cefamandole, fusidic acid, rifampin, and vancomycin. Incubation was at 30 or 35 degrees C for 24, 48, and 72 h. The broth media were supplemented with 2% NaCl for some antimicrobial agents, and the agar dilution method was used with and without the addition of 4% NaCl. The CNS were identified to species by the method of Kloos and Schleifer. The results showed a lack of concordance between two hospitals with respect to oxacillin susceptibility testing by agar dilution with no NaCl supplement. The reasons are not clear but may be related to variations in media. The 4% NaCl supplement or extended incubation to 48 h eliminated this difference. The cefazolin and cefotaxime susceptibility results in the agar disk diffusion test were unreliable if accepted at face value. Cefamandole testing correlated well with the reference method regardless of the method used, and salt supplementation is not recommended. Most of the oxacillin-resistant CNS were resistant to the other beta-lactam drugs except cefamandole. Of 22 CNS resistant to cefamandole, 21 were S. haemolyticus.

Survey of anaerobic susceptibility patterns in Canada

The in vitro activity of penicillin, cefoxitin, moxalactam, ticarcillin, clindamycin, chloramphenicol, and metronidazole against 590 anaerobic isolates collected from five Canadian hospitals during 1984 was determined by an agar dilution technique. Cefoxitin, clindamycin, chloramphenicol, and metronidazole were very active against most of the isolates. No major regional differences in the susceptibility patterns were observed.

In vitro cytotoxicity and antibiotic activity of polymyxin B nonapeptide

Polymyxin B nonapeptide, prepared by enzymic removal of the fatty acyl diaminobutyric acid side chain from polymyxin B, was about 100-fold less toxic to K562 cells than polymyxin B. MICs of polymyxin B nonapeptide against a test panel of bacteria were 2- to 64-fold lower than those of polymyxin B.