Epidemiology of seasonal influenza: use of surveillance data and statistical models to estimate the burden of disease.

The US Centers for Disease Control and Prevention (CDC) uses a 7-component national surveillance system for influenza that includes virologic, influenza-like illness, hospitalization, and mortality data. In addition, some states and health organizations collect additional influenza surveillance data that complement the CDC's surveillance system. Current surveillance data from these programs, together with national hospitalization and mortality data, have been used in statistical models to estimate the annual burden of disease associated with influenza in the United States for many years. National influenza surveillance data also have been used in suitable models to estimate the possible impact of future pandemics. As part of the public health response to the 2003-2004 influenza season, which was noteworthy for its severe effect among children, new US surveillance activities were undertaken. Further improvements in national influenza surveillance systems will be needed to collect and analyze data in a timely manner during the next pandemic.

Epidemiology of pandemic influenza: use of surveillance and modeling for pandemic preparedness.

Along with continual enhancement of current influenza surveillance programs, pandemic preparedness also involves application of current surveillance techniques to past pandemics to identify their viruses and patterns, as well as estimation of the potential burden of future pandemics. Although mortality surveillance has been in place in selected locations for more than a century, the recent development of molecular diagnostics has shed new light on the origin and structure of the viruses responsible for the past 3 pandemics, allowing for comparisons with new viruses identified through ongoing viral surveillance. Models previously used to estimate hospitalizations and mortality associated with past epidemics and pandemics have evolved to estimate the burden and required surge capacity of future pandemics of different severities.

Role of the laboratory in diagnosis of influenza during seasonal epidemics and potential pandemics.

Laboratory diagnosis of influenza is critical to its treatment and surveillance. With the emergence of novel and highly pathogenic avian influenza viruses, the role of the laboratory has been further extended to include isolation and subtyping of the virus to monitor its appearance and facilitate appropriate vaccine development. Recent progress in enhancing testing for influenza promises to both improve the management of patients with influenza and decrease associated health care costs. The present review covers the technological characteristics and utilization features of currently available diagnostic tests, the factors that influence the selection of such tests, and the developments that are essential for pandemic preparedness.

Evaluation of the core antigen assay as a second-line supplemental test for diagnosis of active hepatitis C virus infection.

The British Columbia Center for Disease Control laboratory performs approximately 95% of all hepatitis C virus (HCV) antibody tests for the province's 4 million inhabitants. In 2002, the laboratory tested 96,000 specimens for anti-HCV antibodies, of which 4,800 (5%) were seroreactive and required confirmation of active infection. Although HCV RNA assays with a sensitivity of 50 IU/ml or less are recommended for the confirmation of active HCV infection, given the large number of seroreactive specimens tested annually, we evaluated the Ortho trak-C assay (OTCA) as a second-line confirmatory test and determined its limit of detection (LoD). Of 502 specimens from treatment-naïve anti-HCV-positive individuals, 478 had sufficient volumes for evaluation by the OTCA and HCV RNA tests. Core antigen was not detected in 147 of 478 (30.8%) of these specimens, of which 37 of 147 (25.2%) were shown to be viremic by the VERSANT HCV (version 3.0) (branched-DNA) assay and/or the VERSANT HCV qualitative assay. Testing of 144 replicates of a World Health Organization standard dilution series indicated that the LoD of OTCA was approximately 27,000 IU/ml. This LoD is consistent with the inability of OTCA to detect core antigen in clinical specimens with low viral loads. We conclude that OTCA has limited value as a confirmatory test for the diagnosis of active HCV infection because 37 of 367 (10%) of viremic specimens had undetectable core antigen. Qualitative HCV RNA testing remains the present standard for the confirmation of active HCV infection in the diagnostic setting.

Improved detection of HCV Infection in hemodialysis patients using a new HCV RNA qualitative assay: experience of a transplant center.

BACKGROUND: Hepatitis C virus (HCV) is frequently a silent infection in hemodialysis (HD) patients with a prevalence of 8-10%. Improving HCV detection in this population prior to transplantation is critical both for infection control and optimal patient care. OBJECTIVES: To assess the current HCV testing practice of the National Institute for Transplantation (PCR testing of enzyme immunoassay (EIA) positive HD patients) by evaluating a subset of EIA positive and EIA negative samples with the VERSANT HCV RNA Qualitative Assay based on transcription mediated amplification (HCV Qual (TMA)) (sensitivity < or = 9.6 IU/ml) and in-house PCR (HCV Qual (PCR)) (sensitivity approximately 149 IU/ml). STUDY DESIGN: 2321 HD patients were screened by Abbott HCV EIA 2.0. A subset of 80/169 E IA positive samples and 100/2152 EIA negative samples were tested by both assays. TMA/PCR discordant samples were genotyped. RESULTS: PCR and TMA gave concordant results in 67/80 (83.8%) of EIA positive samples. 11/80 (14.7%) were reactive by HCV Qual (TMA), but not by HCV Qual (PCR); 2/80 (2.7%) were reactive by HCV Qual (PCR), but not by HCV Qual (TMA). 2/100 (2%) EIA negative samples were reactive and 95/100 (95%) were non-reactive by both assays. Three (3%) were only HCV Qual (TMA) reactive. 11/14 TMA+/PCR-samples with sufficient volume were genotyped. CONCLUSIONS: HCV Qual (TMA) identified active HCV infection in more EIA positive and EIA negative patients than HCV Qual (PCR) and should be part of our testing algorithm.

Hepatitis C virus RNA tests: performance attributes and their impact on clinical utility.

The diagnostic market is driven by the burden of disease in the population and the ease or difficulty of disease diagnosis. The efficacy of available therapeutics determines the need for monitoring. Hepatitis C virus currently affects approximately 3% of the world's population, although the overall response rate to the best available therapies is 56%. Research regarding hepatitis C virus remains elusive due to lack of an efficient cell culture system. Diagnosis and monitoring of active hepatitis C virus infection therefore rely on sophisticated molecular tests. This review will focus on current molecular tests for hepatitis C virus RNA and the performance attributes that these tests require for accurate diagnosis and monitoring of infection.

Successful HCV genotyping of previously failed and low viral load specimens using an HCV RNA qualitative assay based on transcription-mediated amplification in conjunction with the line probe assay.

BACKGROUND: Hepatitis C virus (HCV) genotyping is a critical part of the diagnostic work-up for chronic hepatitis C. The VERSANT HCV line probe assay (LiPA) marketed by Bayer Corporation requires PCR-derived amplicons for genotyping usually obtained from commercial assays, including Amplicor HCV 2.0 (Amplicor 2.0), Amplicor HCV Monitor 2.0, or SuperQuant. Occasionally, PCR-based methods in conjunction with LiPA fail to give a genotyping result. Although most genotyping failures occur among low viral load specimens, some occur in specimens with relatively high viral loads. The Bayer HCV RNA Qualitative assay (HCV TMA), with a limit of detection of approximately 5-10 IU/ml, is more sensitive than other commercial assays. OBJECTIVES: An HCV genotyping protocol using HCV TMA linked with LiPA (TMA-LiPA) was developed and tested for ability to genotype samples that had previously failed genotyping by PCR-based methods in conjunction with LiPA. STUDY DESIGN: Clinical specimens were obtained from eight independent laboratories in Canada and the US and tested with TMA-LiPA at the Bayer Reference Testing Laboratory. Specimens included those that failed to produce a genotype result when a PCR-based assay was used in conjunction with LiPA and specimens for which genotyping was not attempted because the viral load was below the validated cut-off determined in the laboratory of origin. RESULTS AND CONCLUSIONS: TMA-LiPA successfully genotyped 68 of 75 (90.7%) specimens that had failed genotyping by PCR-based methods used in conjunction with LiPA and 36 of 40 (90.0%) specimens that were rejected for genotyping due to low viral load. Moreover, TMA-LiPA assigned subtype for 79 of 107 (73.8%) specimens. Our TMA-LiPA results reflected the distribution of HCV genotypes found in North America, and were 100% concordant with those of Amplicor 2.0 in conjunction with LiPA for control specimens genotyped by both assays. TMA-LiPA may prove useful both in optimizing LiPA performance and genotyping patient specimens.

Multicenter evaluation of the VERSANT HCV RNA qualitative assay for detection of hepatitis C virus RNA.

We report the results of a multicenter evaluation of a new assay for the detection of hepatitis C virus (HCV) RNA in human serum or plasma based on transcription-mediated amplification (HCV TMA). Analysis of combined data obtained from 15 independent sites, including 4 sites in the United States and 11 in Europe, by using preproduction kits showed a limit of detection of 9.8 IU/ml and an overall mean specificity of 97.9%. In addition, assay runs and samples were valid consistently (97.8% of assay runs and 98.0% of specimen results). Of the 15 sites that participated in the multicenter evaluation, 2 subsequently carried out additional performance studies with production kits in support of the assay's registration in France. Comparison of the findings from these two sites during the multicenter evaluation and during the registration studies showed an overall improvement in assay performance. A statistically significant (P < 0.001) improvement was achieved for both specificity and specimen validity in the registration studies, which were 99.4 and 98.1%, respectively. Combined data from the two sites showed a lower limit of detection of approximately 2.4 IU/ml and an improved assay validity of 100%, although the sample size was too small to show statistical significance at the 0.05 level. In summary, the performance characteristics of HCV TMA indicate that this assay is a reliable tool for the detection of HCV RNA in serum or plasma. Improvement in assay performance has been demonstrated with refinement of assay reagents, instrumentation, and operator experience.

Performance evaluation of the VERSANT HCV RNA qualitative assay by using transcription-mediated amplification.

A preclinical evaluation of a qualitative assay for the detection of hepatitis C virus (HCV) RNA by transcription-mediated amplification (TMA) was conducted according to the guidelines of the National Committee for Clinical Laboratory Standards and the U.S. Food and Drug Administration. Our results showed that this assay, HCV TMA, detected 95% of samples with HCV RNA concentrations of 5.3 IU/ml and 29 copies/ml. HCV TMA showed an overall specificity of 99.6% and was highly reproducible, detecting 99.3% of samples with HCV RNA concentrations of 50 copies/ml across seven different lots of reagents. Experiments with clinical samples showed that HCV TMA detected all HCV genotypes with similar efficiencies, detecting > or = 95% of samples at 50 HCV RNA copies/ml from patients infected with HCV genotypes 1a, 2b, 3a, 4a, 5a, and 6a. In experiments with RNA transcripts, HCV TMA detected > or = 96.6% of transcripts derived from HCV genotypes 1a, 1b, 2a, 2c, 3a, 4a, 5a, and 6a at 50 HCV RNA copies/ml. Detection of transcripts derived from HCV genotype 2b was slightly lower (88.4%) at 50 copies/ml but was 97.0% at 75 copies/ml. In addition, HCV TMA exhibited robust performance in detecting HCV RNA in samples subjected to various conditions commonly encountered in a clinical laboratory, including long-term storage, multiple freeze-thaw cycles, different collection tubes, and the presence of endogenous substances, commonly prescribed drugs, or other microorganisms and viruses. With its high sensitivity, specificity, reproducibility, and equivalent genotype reactivity, HCV TMA may provide an attractive alternative for routine qualitative HCV RNA testing in clinical laboratories.

Qualitative detection of hepatitis C virus RNA: comparison of analytical sensitivity, clinical performance, and workflow of the Cobas Amplicor HCV test version 2.0 and the HCV RNA transcription-mediated amplification qualitative assay.

The qualitative Cobas Amplicor hepatitis C virus (HCV) version 2.0 assay (HCV PCR) and the Bayer Reference Testing Laboratory HCV RNA transcription-mediated amplification assay (HCV TMA) were compared for analytical sensitivity, clinical performance, and workflow. Limits of detection were determined by testing dilutions of the World Health Organization HCV standard in replicates of 15 at concentrations of from 1.0 to 70 IU/ml. The limit of detection of the HCV PCR assay was calculated to be 45 IU/ml on initial testing and 32 IU/ml after resolution of gray zone results. The calculated limit of detection for HCV TMA was 6 IU/ml. To compare clinical performance, 300 specimens, grouped as follows, were evaluated: 112 samples that were indeterminate in an anti-HCV enzyme immunoassay (EIA) and for which HCV RNA was not detected by HCV PCR; 79 samples that were EIA positive and for which HCV RNA was not detected by HCV PCR; and 105 samples that were both EIA and HCV PCR positive. For these groups, interassay concordance ranged from 96.2% to 100%. In addition, three HCV PCR gray zone specimens and one neonatal specimen were also evaluated. A 64-sample run (full run, 91 specimens) required 5 h for testing by HCV TMA, whereas almost 8 h were required to test a full run of 22 specimens by HCV PCR. HCV TMA demonstrated excellent concordance with HCV PCR when clinical samples were tested. However, HCV TMA was more sensitive than HCV PCR, required less time for test result completion, and had a greater throughput.