Triggers for switching from minipool testing by nucleic acid technology to individual-donation nucleic acid testing for West Nile virus: analysis of 2003 data to inform 2004 decision making

Performance of Nucleic Acid Amplification Tests for Detection of Severe Acute Respiratory Syndrome Coronavirus 2 in Prospectively Pooled Specimens

Pooled nucleic acid amplification tests for severe acute respiratory syndrome coronavirus 2 could increase availability of testing at decreased cost. However, the effect of dilution on analytical sensitivity through sample pooling has not been well characterized. We tested 1,648 prospectively pooled specimens by using 3 nucleic acid amplification tests for severe acute respiratory syndrome coronavirus 2: a laboratory-developed real-time reverse transcription PCR targeting the envelope gene, and 2 commercially available Panther System assays targeting open reading frame 1ab. Positive percent agreement (PPA) of pooled versus individual testing ranged from 71.7% to 82.6% for pools of 8 and from 82.9% to 100.0% for pools of 4. We developed and validated an independent stochastic simulation model to estimate effects of dilution on PPA and efficiency of a 2-stage pooled real-time reverse transcription PCR testing algorithm. PPA was dependent on the proportion of tests with positive results, cycle threshold distribution, and assay limit of detection.

Correlation of West Nile Virus Incidence in Donated Blood with West Nile Neuroinvasive Disease Rates, United States, 2010-2012

Over the past decade, West Nile virus (WNV) has spread across the United States. We aggregated blood donor data from 2010–2012 and then calculated the incidence of WNV RNA–positive donations and compared the incidence with neuroinvasive disease (NID) case data from the ArboNET surveillance system. Of 10,107,853 donations, 640 were confirmed positive. The seasonal WNV incidence rate per 100,000 persons was 33.4 (95% CI 22–45) in 2010, 25.7 (95% CI 15–34) in 2011, and 119.9 (95% CI 98–141) in 2012. NID to blood donor ratios were 1 in 164 (95% CI 152–178) in 2010, 1 in 158 (95% CI 145–174) in 2011, and 1 in 131 (95% CI 127–136) in 2012. We updated estimates of the ratio of NID to WNV infection rates, demonstrating stable disease penetrance over the study period. Blood donor WNV RNA screening is a valuable public health tool for WNV surveillance.

Climate change projections of West Nile virus infections in Europe: implications for blood safety practices

BACKGROUND

West Nile virus (WNV) is transmitted by mosquitoes in both urban as well as in rural environments and can be pathogenic in birds, horses and humans. Extrinsic factors such as temperature and land use are determinants of WNV outbreaks in Europe, along with intrinsic factors of the vector and virus.

METHODS

With a multivariate model for WNV transmission we computed the probability of WNV infection in 2014, with July 2014 temperature anomalies. We applied the July temperature anomalies under the balanced A1B climate change scenario (mix of all energy sources, fossil and non-fossil) for 2025 and 2050 to model and project the risk of WNV infection in the future. Since asymptomatic infections are common in humans (which can result in the contamination of the donated blood) we estimated the predictive prevalence of WNV infections in the blood donor population.

RESULTS

External validation of the probability model with 2014 cases indicated good prediction, based on an Area Under Curve (AUC) of 0.871 (SD = 0.032), on the Receiver Operating Characteristic Curve (ROC). The climate change projections for 2025 reveal a higher probability of WNV infection particularly at the edges of the current transmission areas (for example in Eastern Croatia, Northeastern and Northwestern Turkey) and an even further expansion in 2050. The prevalence of infection in (blood donor) populations in the outbreak-affected districts is expected to expand in the future.

CONCLUSIONS

Predictive modelling of environmental and climatic drivers of WNV can be a valuable tool for public health practice. It can help delineate districts at risk for future transmission. These areas can be subjected to integrated disease and vector surveillance, outreach to the public and health care providers, implementation of personal protective measures, screening of blood donors, and vector abatement activities.

West Nile virus infection incidence based on donated blood samples and neuroinvasive disease reports, Northern Texas, USA, 2012

During the 2012 outbreak of West Nile virus in the United States, approximately one third of the cases were in Texas. Of those, about half occurred in northern Texas. Models based on infected blood donors and persons with neuroinvasive disease showed, respectively, that ≈0.72% and 1.98% of persons in northern Texas became infected.

Implementation of NAT Screening for West Nile Virus and Experience with Seasonal Testing in Germany

BACKGROUND

West Nile virus (WNV) can be transmitted by transfusion through infected blood components. In Germany, a 28-day deferral for blood donors of therapeutic blood components who had spent at least 2 days in WNV-endemic areas from June 1 to November 30, 2014 was enforced. Otherwise, screening of blood donors for WNV RNA or the application of pathogen reduction techniques are appropriate alternatives.

METHODS

In the present study, we evaluated NAT screening for the detection of WNV in blood components. A total of 58 minipools consisting of 357 individual blood donors were screened for the presence of WNV RNA employing an automated high-volume extraction method using the RealStar WNV RT-PCR Kit. Additionally, different WNV reference reagents were quantified to prove the status quo of standardization. Four different WNV real-time NAT kits were compared using samples of an external quality assessment panel.

RESULTS

The 95% lower detection limit of the WNV MP-NAT was determined to 30.2 copies/ml (95% CI 24.2-45.4 copies/ml). No WNV RNA-positive minipool was detected. Quantification of WNV reference reagents revealed shortcomings in standardization. Comparison of several WNV NAT assays showed considerable differences in assay sensitivities and particularly a missing detection of WNV lineage 2. Implementation of seasonal WNV MP-NAT screening was demonstrated.

CONCLUSION

Actually, WNV infections in Germany are rare events introduced by returning travelers, but surveillance of these emerging infections is important for safety in blood supply. The validation study pointed out the need for standardization of WNV NAT because of current lack of an international standard for WNV RNA.

West Nile virus lineage 2 infection in a blood donor from Vienna, Austria, August 2014

Eastern Austria is neighbouring regions with ongoing West Nile virus (WNV) transmissions. Three human WNV infections had been diagnosed during the past decade in Austria. The Austrian Red Cross Blood Service (ARC-BS) started a first voluntary screening for WNV in blood donors from Eastern Austria by Nucleic Acid Testing (NAT) in June 2014. This is also the most extensive WNV surveillance programme in humans in Austria so far. In August 2014, one autochthonous WNV infection was detected in a blood donor from Vienna. By now, one in 67,800 whole blood donations was found to be positive for WNV RNA.

Current epidemiology and clinical practice in arboviral infections - implications on blood supply in South-East Asia

Arthropod-borne viruses (arboviruses) are a growing threat to global health. Complex vector-virus-host interactions lead to unpredictable epidemiological patterns. Difficulties in accurate surveillance including imperfect diagnostic tools impair effective response to outbreaks. With arboviral infections causing a wide spectrum of disease severity, from asymptomatic infection to fatal neuroinvasive and haemorrhagic fevers, the potential impact on blood safety is significant. Asymptomatic or presymptomatic individuals may introduce virus into the blood supply by donation, while recipients can potentially suffer severe consequences. Dengue, West Nile and chikungunya outbreaks have led to responses by blood transfusion services which can inform future planning. Reports of transfusion-associated transmission demonstrate the potentially fatal consequences of lack of haemovigilance. South-East Asia remains vulnerable to arboviruses with permissive climate and high levels of endemic transmission as well as the potential for emerging and re-emerging arboviral diseases. Resource limitations constrain the use of expensive technologies for donor screening. Continued surveillance and research will be required to manage the arboviral threat to the blood supply.

West Nile virus state of the art report of MALWEST Project

During the last three years Greece is experiencing the emergence of West Nile virus (WNV) epidemics. Within this framework, an integrated surveillance and control programme (MALWEST project) with thirteen associate partners was launched aiming to investigate the disease and suggest appropriate interventions. One out of seven work packages of the project is dedicated to the State of the Art report for WNV. Three expert working groups on humans, animals and mosquitoes were established. Medical databases (PubMed, Scopus) were searched together with websites: e.g., WHO, CDC, ECDC. In total, 1,092 relevant articles were initially identified and 258 of them were finally included as references regarding the current knowledge about WNV, along with 36 additional sources (conference papers, reports, book chapters). The review is divided in three sections according to the fields of interest: (1) WNV in humans (epidemiology, molecular characteristics, transmission, diagnosis, treatment, prevention, surveillance); (2) WNV in animals (epidemiological and transmission characteristics concerning birds, horses, reptiles and other animal species) and (3) WNV in mosquitoes (control, surveillance). Finally, some examples of integrated surveillance programmes are presented. The introduction and establishment of the disease in Greece and other European countries further emphasizes the need for thorough research and broadening of our knowledge on this viral pathogen.

West Nile virus infection in blood donors in the New York City area during the 2010 seasonal epidemic

BACKGROUND

A uniform threshold strategy for converting from minipool (MP)-nucleic acid testing (NAT) to individual donation (ID)-NAT screening for acute West Nile virus (WNV) infection among blood donors is lacking. We report on WNV screening at the New York Blood Center during the 2010 seasonal WNV epidemic, the most severe epidemic in that state since the original outbreak in 1999.

STUDY DESIGN AND METHODS

Between July 1 and October 31, 2010, blood donations were screened by MP-NAT or ID-NAT and the presence of anti-WNV immunoglobulin (Ig)M and IgG was evaluated among NAT-positive donations.

RESULTS

Twenty presumed viremic donations were identified for a frequency of 0.0129% (1 in 7752 donations). Nine donations that could have been missed by MP-NAT were identified. Two of these donations were both IgM and IgG negative, one of which would have been missed if more than one positive donation was required for initiating ID-NAT. Retrospective ID-NAT revealed two positive donations. The majority of the NAT-positive donations in New York (16/19) were from donors who lived in counties that had the highest incidence of human WNV cases in the state.

CONCLUSION

Our data details the identification of WNV NAT-positive blood donations during a severe seasonal epidemic in the New York area. By initiating ID-NAT after one positive donation, using retrospective testing, and triggering ID-NAT regionally, we were able to prevent the release of presumably infectious donations. The detection of NAT-positive donations with retrospective testing, however, may indicate the need for changes in our trigger criteria.

West Nile story: the transfusion medicine chapter

West Nile virus first arrived in North America in the late summer of 1999. Since then it has established itself in Canada and the USA, causing outbreaks every summer since then. The emergence of a new virus prompted a great deal of public health activity and posed a new challenge to the organizations that collect, test, process and supply blood products, in terms of the prevention of transfusion transmission. The rapid development and implementation of effective and innovative donor testing strategies highlights the importance of collaboration, both national and international, and creative thinking as we prepare for the future and the microbial challenges we will certainly face.

West Nile virus in 2006 and 2007: the Canadian Blood Services' experience

BACKGROUND

The Canadian blood supply has been screened for West Nile virus (WNV) since 2003. A strategy for targeted individual-donation nucleic acid testing (ID-NAT) was implemented in 2004 to identify potentially infectious donations that may be missed by minipool (MP) testing. In 2007, Canada experienced a larger epidemic than in previous years providing an opportunity to evaluate the ID-NAT triggering algorithm in higher-risk areas.

STUDY DESIGN AND METHODS

A specially created database and internal-external communication identified regions for targeted ID-NAT using MP and community triggers. WNV-positive donations identified by ID-NAT were reexamined in MP to assess the efficacy of targeted ID-NAT in identifying potentially infectious donations that may have been missed by MP testing. WNV-positive donation data from 2006 and 2007 were analyzed to examine temporal and geographic trends. A telephone survey about symptoms was carried out after the 2007 season.

RESULTS

In total 78 WNV-positive donations were identified (66 true-positives and four false-positives being in 2007). Most positive donations were in the late summer, concentrated in the same western provinces as community cases. Fifty-two donations were identified by ID-NAT and 46% were consistently positive in MP. Of the other 54%, 74% were immunoglobulin (Ig)M- and/or IgG-positive. Fifty-six percent of donors experienced mostly mild symptoms before or after donation (but all said they were well at the time of donation).

CONCLUSION

WNV-positive donations correspond geographically with the epidemic. MP testing identifies most potentially infectious donations with a smaller potential benefit from targeted ID-NAT. Mild symptoms are common but may not deter donation.

Health economics of blood transfusion safety--focus on sub-Saharan Africa

BACKGROUND AND OBJECTIVES

Health economics provides a standardised methodology for valid comparisons of interventions in different fields of health care. This review discusses the health economic evaluations of strategies to enhance blood product safety in sub-Saharan Africa.

METHODS

We reviewed health economic methodology with special reference to cost-effectiveness analysis. We searched the literature for cost-effectiveness in blood product safety in sub-Saharan Africa.

RESULT

HIV-antibody screening in different settings in sub-Saharan Africa showed health gains and saved costs. Except for adding HIV-p24 screening, adding other tests such as nucleic acid amplification testing (NAT) to HIV-antibody screening displayed incremental cost-effectiveness ratios greater than the WHO/World Bank specified threshold for cost-effectiveness. The addition of HIV-p24 in combination with HCV antibody/antigen screening and multiplex (HBV, HCV and HIV) NAT in pools of 24 may also be cost-effective options for Ghana.

CONCLUSIONS

From a health economic viewpoint, HIV-antibody screening should always be implemented in sub-Saharan Africa. The addition of HIV-p24 antigen screening, in combination with HCV antibody/antigen screening and multiplex (HBV, HCV and HIV) NAT in pools of 24 may be feasible options for Ghana. Suggestions for future health economic evaluations of blood transfusion safety interventions in sub-Saharan Africa are: mis-transfusion, laboratory quality and donor management.

Associations between West Nile virus infection and symptoms reported by blood donors identified through nucleic acid test screening

BACKGROUND

Blood collected in the United States and Canada is screened for West Nile virus (WNV) using nucleic acid testing (NAT). The role that donor-reported symptoms of infection disclosed at or shortly after donation may play in enhancing blood safety has been debated. Little data are available on subsequent manifestations of WNV-specific disease outcomes in viremic donors.

STUDY DESIGN AND METHODS

Donors with initially reactive NAT results were informed by telephone and asked to complete symptom interviews. The questionnaires are focused on three time periods: the week before, the day of, and the 2 weeks after donation. Symptoms and risk factors were compared between confirmed-positive and false-positive donors (classified based on confirmatory NAT and serology). Additional analyses comparing confirmed-positive symptomatic and asymptomatic donors were conducted.

RESULTS

A total of 423 of 536 initially reactive donors were interviewed between 2003 and 2006: 292 confirmed-positive for WNV and 131 false-positive. Individual symptoms were not significant predictors of WNV infection, except skin rash in the week before donation (odds ratio [OR], 3.0; 95% confidence interval [CI], 1.2-7.9) and body aches in the period after donation (OR, 2.8; 95% CI, 1.1-7.4). Specific combinations of symptoms were not good predictors of infection, but donors with three or more concurrent symptoms before donation were more likely to have WNV infection (OR, 2.5; 95% CI, 1.2-5.1). Demographic characteristics, predonation symptoms, and serology profiles in confirmed-positive donors did not predict postdonation symptom severity. Thirty-five confirmed-positive donors (12%) sought medical care for WNV infection, with two hospitalizations, but no cases of neuroinvasive disease.

CONCLUSION

The number rather than type of symptoms is associated with confirmed WNV infection, but the overall predictive value is low. Very few infected donors develop clinically significant disease.

Virus and antibody dynamics in acute west nile virus infection

BACKGROUND

The dynamics of the early stages of West Nile virus (WNV) infection can be assessed by follow-up studies of viremic blood donors.

METHODS

A total of 245 donors with WNV viremia were followed up weekly for 4 weeks and then monthly for up to 6 additional months or until seroconversion. Plasma samples were tested for WNV RNA by transcription-mediated amplification (TMA) and for WNV-specific IgM and IgG antibodies. RNA persistence was investigated by 6 replicate TMA tests; samples that were viremic for >40 days were tested for WNV-neutralizing activity. Follow up of 35 additional viremic donors for up to 404 days was conducted to evaluate persistence of WNV-specific antibody.

RESULTS

The median time from RNA detection to IgM seroconversion was 3.9 days; to IgG seroconversion, 7.7 days; to RNA negativity by single-replicate TMA, 13.2 days; and to RNA negativity by 6-replicate TMA, 6.1 additional days after results of single-replicate TMA are negative. For 4 donors in whom RNA persisted for >40 days after the index donation, all samples obtained after this threshold were also positive for WNV IgG and neutralizing activity. The mean times to IgM and IgA negativity were 156 and 220 days, respectively.

CONCLUSIONS

IgM and IgG develop rapidly after viremia and before RNA levels become undetectable, which occurred a mean of 13.2 days after the index donation among donors in this study. WNV RNA detection by replicate TMA rarely persists for >40 days after the index donation and is accompanied by WNV-specific neutralizing antibody, consistent with an absence of WNV transmission via transfusion of seropositive blood components.

West Nile Virus Adheres to Human Red Blood Cells in Whole Blood

Background. West Nile virus (WNV) is endemic in the United States. It is transmissible by blood transfusion, and the nation's blood supply is currently screened for WNV. Documented transmission of WNV infection through red blood cell (RBC) units in which the plasma co-component had a low viral load could be explained, in at least 1 instance, by cell-association of WNV; in this case, the RBC unit was released as negative by minipool nucleic acid testing (NAT) performed on plasma but was intermittently NAT-positive when subsequently tested as an individual sample. We hypothesized that a proportion of WNV bound to blood cells and was not measured by NAT performed on plasma samples. We have investigated whether WNV binds to RBCs, leading to reduction of WNV RNA detection by NAT performed on plasma samples.Methods. Equal volumes of leukoreduced RBCs and their corresponding plasma components from 20 blood donors with NAT results that were positive for WNV were tested in 5 replicates by reverse-transcriptase polymerase chain reaction TaqMan for WNV. In addition, aliquots from 8 of the RBC units were tested by infectivity assays using Vero cells.Results. The reverse-transcriptase polymerase chain reaction TaqMan assay showed that the viral load in the RBC components exceeded that in the corresponding plasma units by 1 order of magnitude. In addition, viruses associated with the RBCs were infectious in Vero cell cultures.Conclusions. These observations reinforce the notion that extraction of viral RNA from whole blood could improve assay sensitivity for blood donor screening and further reduce the residual risk of WNV transmission through transfusion.

Performance evaluation of the PROCLEIX® West Nile virus assay on semi-automated and automated systems

The PROCLEIX West Nile virus assay (WNV assay) is a qualitative nucleic acid test based on transcription-mediated amplification (TMA). The assay was used under an investigational protocol in the United States to screen blood donations for West Nile virus (WNV) RNA starting in the summer of 2003, and was licensed by the FDA in December 2005 for use on the PROCLEIX System, also known as the enhanced semi-automated system (eSAS). Performance characteristics for the assay were determined on both eSAS and the fully automated PROCLEIX TIGRIS (TIGRIS) System. Detection of both lineage 1 and lineage 2 WNV was demonstrated on both systems. For lineage 1, the 95% detection limit was 8.2 copies/ml for eSAS and 9.8 copies/ml for the TIGRIS system. For lineage 2, > or =95% detection was seen at > or =30 copies/ml on both systems. The overall specificity of the assay was >99.9% in fresh and frozen plasma specimens. Reproducibility studies on the TIGRIS system yielded > or =99.1% agreement with expected results for the 3-member panel tested (0, 30, and 100 copies/ml). The WNV assay exhibited robust performance in cadaveric specimens and specimens representing various donor and donation conditions, including specimens from different plasma collection tubes that were subjected to multiple freeze/thaw cycles; specimens with elevated levels of endogenous substances; specimens containing other viruses and microorganisms; and specimens from patients with autoimmune and other diseases. Overall, these studies demonstrate high sensitivity, specificity, and reproducibility of the WNV assay on both the semi-automated and automated systems.

Blood Screening for West Nile Virus: The Cost-Effectiveness of a Real-Time, Trigger-Based Strategy

Previous studies have demonstrated that universal blood screening for West Nile virus is not cost-effective. A newly proposed, real-time, trigger-based screening strategy was analyzed and was also shown to be not cost-effective. These results were highly sensitive to pricing of screening assays.

West Nile virus infections projected from blood donor screening data, United States, 2003

Routine donor nucleic acid amplification testing is a valuable surveillance screening tool.

National blood donor screening for West Nile virus (WNV) RNA using minipool nucleic acid amplification testing (MP-NAT) was implemented in the United States in July 2003. We compiled national NAT yield data and performed WNV immunoglobulin M (IgM) testing in 1 WNV-epidemic region (North Dakota). State-specific MP-NAT yield, antibody seroprevalence, and the average time RNA is detectable by MP-NAT were used to estimate incident infections in 2003. WNV donor screening yielded 944 confirmed viremic donors. MP-NAT yield peaked in August with >0.5% of donations positive for WNV RNA in 4 states. Peak IgM seroprevalence for North Dakota was 5.2% in late September. The average time viremia is detectable by MP-NAT was 6.9 days (95% confidence interval [CI] 3.0–10.7). An estimated 735,000 (95% CI 322,000–1,147,000) infections occurred in 2003, with 256 (95% CI 112–401) infections per neuroinvasive case. In addition to preventing transfusion-transmitted WNV infection, donor screening can serve as a tool to monitor seasonal incidence in the general population.

The Development of West Nile Virus Safety Policies by Canadian Blood Services: Guiding Principles and a Comparison Between Canada and the United States

To address the emerging threat of West Nile virus (WNV) to the blood supply, Canadian Blood Services (CBS) made a series of policy decisions that were either similar to those adopted in the United States or more stringent than policies formulated in the United States at the same time. More stringent Canadian policies included the development of an in-house WNV RNA assay, the stockpiling of frozen plasma components in the winter for transfusion in WNV-affected areas in the summer, a special recruitment campaign for red blood cell collections before the start of the 2003 WNV season, and an inventory exchange (ie, WNV-tested for untested red blood cells) initiated 2 weeks after the onset of WNV screening, as well as the implementation of targeted individual-donation WNV testing on August 2, 2004, in the absence of any positive donors or clinical cases of WNV infection in Canada. The general principles that guided CBS decision making with regard to WNV safety included application of the precautionary principle, harmonization with policies in the United States, a consideration of logistic issues, compliance with Health Canada requests, responsiveness to public expectations about transfusion safety, and transparency in decision making with timely communication to stakeholders. Before implementing WNV blood safety policies, CBS assessed their impact on blood availability. When policies were implemented, data were obtained quickly to ensure that the prior impact assessments were accurate. This review discusses the guiding principles affecting CBS policy development and compares CBS WNV safety policies to policies adopted in the United States.

West Nile Virus Infections Projected from Blood Donor Screening Data, United States, 2003

National blood donor screening for West Nile virus (WNV) RNA using minipool nucleic acid amplification testing (MP-NAT) was implemented in the United States in July 2003. We compiled national NAT yield data and performed WNV immunoglobulin M (IgM) testing in 1 WNV-epidemic region (North Dakota). State-specific MP-NAT yield, antibody seroprevalence, and the average time RNA is detectable by MP-NAT were used to estimate incident infections in 2003. WNV donor screening yielded 944 confirmed viremic donors. MP-NAT yield peaked in August with >0.5% of donations positive for WNV RNA in 4 states. Peak IgM seroprevalence for North Dakota was 5.2% in late September. The average time viremia is detectable by MP-NAT was 6.9 days (95% confidence interval [CI] 3.0-10.7). An estimated 735,000 (95% CI 322,000-1,147,000) infections occurred in 2003, with 256 (95% CI 112-401) infections per neuroinvasive case. In addition to preventing transfusion-transmitted WNV infection, donor screening can serve as a tool to monitor seasonal incidence in the general population.

Cost-effectiveness of alternative blood-screening strategies for West Nile Virus in the United States

BACKGROUND

West Nile virus (WNV) is endemic in the US, varying seasonally and by geographic region. WNV can be transmitted by blood transfusion, and mandatory screening of blood for WNV was recently introduced throughout the US. Guidelines for selecting cost-effective strategies for screening blood for WNV do not exist.

METHODS AND FINDINGS

We conducted a cost-effectiveness analysis for screening blood for WNV using a computer-based mathematical model, and using data from prospective studies, retrospective studies, and published literature. For three geographic areas with varying WNV-transmission intensity and length of transmission season, the model was used to estimate lifetime costs, quality-adjusted life expectancy, and incremental cost-effectiveness ratios associated with alternative screening strategies in a target population of blood-transfusion recipients. We compared the status quo (baseline screening using a donor questionnaire) to several strategies which differed by nucleic acid testing of either pooled or individual samples, universal versus targeted screening of donations designated for immunocompromised patients, and seasonal versus year-long screening. In low-transmission areas with short WNV seasons, screening by questionnaire alone was the most cost-effective strategy. In areas with high levels of WNV transmission, seasonal screening of individual samples and restricting screening to blood donations designated for immunocompromised recipients was the most cost-effective strategy. Seasonal screening of the entire recipient pool added minimal clinical benefit, with incremental cost-effectiveness ratios exceeding USD 1.7 million per quality-adjusted life-year gained. Year-round screening offered no additional benefit compared to seasonal screening in any of the transmission settings.

CONCLUSIONS

In areas with high levels of WNV transmission, seasonal screening of individual samples and restricting screening to blood donations designated for immunocompromised recipients is cost saving. In areas with low levels of infection, a status-quo strategy using a standard questionnaire is cost-effective.

West Nile Virus: Epidemiology and Clinical Features of an Emerging Epidemic in the United States

West Nile virus (WNV) was first detected in North America in 1999 during an outbreak of encephalitis in New York City. Since then the virus has spread across North America and into Canada, Latin America, and the Caribbean. The largest epidemics of neuroinvasive WNV disease ever reported occurred in the United States in 2002 and 2003. This paper reviews new information on the epidemiology and clinical aspects of WNV disease derived from greatly expanded surveillance and research on WNV during the past six years.

Relative sensitivities of licensed nucleic acid amplification tests for detection of viremia in early human immunodeficiency virus and hepatitis C virus infection

BACKGROUND

Screening donors for human immunodeficiency virus (HIV) and hepatitis C virus (HCV) RNA is primarily performed on minipools (MPs) with one of two commercial nucleic acid amplification tests (NAT; Roche Molecular Systems; or Gen-Probe/Chiron). We compared these assays with respect to detection of RNA in early HIV and HCV infection.

STUDY DESIGN AND METHODS

Twelve HIV plasma donor panels (116 serial samples) and 12 HCV panels (180 serial samples) were selected to optimally represent early viremia. Initial testing was performed in singlicate or triplicate on separately coded aliquots, both neat and at dilutions corresponding to MP screening (1:16 for Gen-Probe; 1:24 for Roche); 20 additional replicates were performed when discordant results were observed. Odds ratios (ORs) comparing detection of RNA by different assays were derived with logistic regression models. Differences in window-period closure and yields of assays in MP or individual-donation (ID) format were estimated.

RESULTS

Differences in detection rates between Roche and Gen-Probe NAT assays were small and only observed with samples with very-low-level viremia. ORs for detecting RNA by the Gen-Probe versus the Roche assay were significant for HIV if conducted on MPs (1.8; 95% confidence interval [CI], 1.3-2.5) but not neat (1.0; 95% CI, 0.72-1.4). Odds of detecting HCV RNA were higher if the Gen-Probe assay was conducted either neat (2.3; 95% CI, 1.6-3.2) or on MPs (4.0; 95% CI, 2.8-5.8). These differences translated to <1 day window-period closure and

CONCLUSIONS

Differences in sensitivities of licensed NAT assays for HIV and HCV are very small and clinically insignificant, particularly when compared to differences of MP versus ID NAT screening.

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Key Words Collapse

MESH Headings

• Blood Banking/methods
• HIV/genetics
• HIV/isolation & purification
• HIV Infections/blood
• HIV Infections/diagnosis
• Hepacivirus/genetics
• Hepacivirus/isolation & purification
• Hepatitis C/blood
• Hepatitis C/diagnosis
• Humans
• Licensure
• Mass Screening/methods
• Nucleic Acid Amplification Techniques/methods
• RNA, Viral/blood
• RNA, Viral/isolation & purification
• Sensitivity and Specificity
• Viremia/blood
• Viremia/diagnosis

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Grants

• N01-HB-47114 NHLBI NIH HHS
• N01-HB-97077 NHLBI NIH HHS
• N01-HB-97078 NHLBI NIH HHS
• N01-HB-97079 NHLBI NIH HHS
• N01-HB-97080 NHLBI NIH HHS
• N01-HB-97081 NHLBI NIH HHS
• N01-HB-97082 NHLBI NIH HHS

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Affiliation(s)

Michael P Busch Blood Systems Research Institute, San Francisco, California 94118, USA.
Simone A Glynn
David J Wright
Dale Hirschkorn
Megan E Laycock
Joan McAuley
Yongling Tu
Cristina Giachetti
James Gallarda
John Heitman
Steven H Kleinman

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Utilization of follow-up specimens from viremic blood donors to assess the value of west nile virus immunoglobulin G avidity as an indicator of recent infection

The value of West Nile virus immunoglobulin G avidity for distinguishing recent from past infection was investigated using 348 follow-up specimens from 170 viremic blood donors. Low avidity accurately indicated infection within the previous 4 months. However, due to rapid avidity maturation in some individuals, high avidity did not accurately indicate past infection.

Screening the blood supply for West Nile virus RNA by nucleic acid amplification testing

BACKGROUND

The use of nucleic acid amplification tests of "minipools" of 16 samples to screen blood donors for West Nile virus RNA began in July 2003. We report the yield and characteristics of positive donations and the incremental yield and safety of nucleic acid amplification tests of individual donations.

METHODS

Reactive minipools were analyzed to identify the individual reactive donations. For the regions with the highest yield on minipool testing, retrospective nucleic acid amplification testing was performed on individual donations that were negative on minipool testing. Reactive donations were confirmed by alternative nucleic acid amplification tests and IgM and IgG tests, and donors were followed to document seroconversion.

RESULTS

From July 1 through October 31, 2003, 677,603 donations were prospectively screened for West Nile virus by minipool testing, yielding 183 confirmed viremic donations (0.027 percent, or 1 in 3703 donations). Retrospective individual testing of 23,088 donations from high-prevalence regions that were negative on minipool testing yielded 30 additional units with a low level of viremia, with 14 additional viremic units detected by prospective testing of individual donations late in the 2003 transmission season. Of all the viremic units detected, 5 percent were detected only by individual testing and were negative for IgM antibody, 29 percent were detected by individual testing after IgM seroconversion, and 66 percent were detected by minipool testing. West Nile virus infection was confirmed in both recipients of IgM-negative units that were reactive on individual testing, whereas neither recipient of antibody-positive blood components that were reactive on individual testing was infected. In 2004, prospective testing of individual donations in regions that yielded donations that were reactive on minipool testing resulted in a 32 percent incremental yield of units with a low level of viremia that would have been missed by minipool testing.

CONCLUSIONS

Although nucleic acid amplification testing of minipools of blood donations prevented hundreds of cases of West Nile virus infection in 2003, it failed to detect units with a low level of viremia, some of which were antibody-negative and infectious. These data support the use of targeted nucleic acid amplification testing of individual donations in high-prevalence regions, a strategy that was implemented successfully in 2004.

West Nile virus among blood donors in the United States, 2003 and 2004

BACKGROUND

West Nile virus first appeared in the United States in 1999 and has since spread throughout the contiguous states, resulting in thousands of cases of disease. By 2002, it was clear that the virus could be transmitted by blood transfusion, and by the middle of 2003, essentially all blood donations were being tested for West Nile virus RNA with the use of investigational nucleic acid amplification tests; testing was performed on individual samples or on "minipools" of up to 16 donations.

METHODS

We analyzed data from the West Nile virus testing program of the American Red Cross for 2003 and 2004 to identify geographic and temporal trends. In areas with a high incidence of infection, individual donations were tested to increase the sensitivity of testing. Donors with reactive results participated in follow-up studies to confirm the original reactivity and to assess the natural history of infection.

RESULTS

Routine testing in 2003 and 2004 identified 540 donations that were positive for West Nile virus RNA, of which 362 (67 percent) were IgM-antibody-negative and most likely infectious. Of the 540 positive donations, 148 (27 percent) were detectable only by testing of individual donations, but only 15 of the 148 (10 percent) were negative for IgM antibody. The overall frequencies of RNA-positive donations during the epidemic periods were 1.49 per 10,000 donations in 2003 and 0.44 per 10,000 in 2004. In 2004, 52 percent of the positive donations were from donors in four counties in southern California.

CONCLUSIONS

Rapid implementation of a nucleic acid amplification test led to the prospective identification of 519 donors who were positive for West Nile virus RNA and the removal of more than 1000 potentially infectious related components from the blood supply of the Red Cross. No cases of transfusion-transmitted infection were confirmed among recipients of the tested blood.

Detection of West Nile virus RNA and antibody in frozen plasma components from a voluntary market withdrawal during the 2002 peak epidemic

BACKGROUND

The US West Nile virus (WNV) epidemic in the summer and fall of 2002 included the first documented cases of transfusion-transmitted WNV infection. In December 2002, the FDA supported a voluntary market withdrawal by the blood banking community of frozen blood components collected in WNV high-activity areas. At the time, the prevalence of viremia and serologic markers for WNV in the blood supply was undefined.

STUDY DESIGN AND METHODS

In collaboration with America's Blood Centers, 1468 frozen plasma components (of approx. 60,000 frozen units voluntarily withdrawn from the market) were selectively retrieved from the peak epidemic regions and season (June 23, 2002-September 28, 2002). These units were unlinked, subaliquoted, and tested by WNV enzyme immunoassays (EIAs; Focus Technologies and Abbott Laboratories) and nucleic acid amplification tests (NATs; Gen-Probe Inc. and Roche Molecular Systems).

RESULTS

Of the 1468 EIA results from Abbott and Focus, 7 were anti-immunoglobulin M (IgM)- and anti-immunoglobulin G (IgG)-reactive by both assays, 8 and 1 were IgM-only-reactive, and 8 and 23 were IgG-only-reactive, respectively. NAT by Gen-Probe and Roche Molecular Systems yielded one RNA-positive, antibody-negative unit containing approximately 440 RNA copies per mL. An additional 10-fold replicate NAT testing by Gen-Probe on 14 of 15 IgM-reactive specimens yielded 2 additional IgM- and IgG-reactive units with low-level viremia (i.e., 7/10 and 2/10 replicates tested reactive).

CONCLUSION

The prevalence of acute (RNA-positive) and recent (IgM-seroreactive) WNV infections indicates that transfusion risk in high-risk areas could have been considerable and that voluntary market withdrawal of frozen components likely averted some WNV transfusion transmissions. The existence of very-low-level viremic units raises concerns, because WNV minipool NAT screening will miss such units and individual NAT may not completely correct this situation.

The 2003 West Nile virus United States epidemic: the America's Blood Centers experience

BACKGROUND

A detailed assessment of West Nile virus (WNV) yield is needed to evaluate the effectiveness of the WNV nucleic acid amplification technology (NAT) screening implemented in 2003.

STUDY DESIGN AND METHODS

WNV NAT screening and donation data were compiled from members of America's Blood Centers, which collect nearly 50 percent of the US blood supply. WNV RNA screening was performed with either the Gen-Probe/Chiron Procleix transcription-mediated amplification assay or the Roche TaqScreen polymerase chain reaction. Results of alternate NAT and WNV immunoglobulin M (IgM) antibody assays conducted on index and follow-up samples were obtained from test manufacturers. Presumed WNV positivity was based on NAT repeat reactivity of the individual index donation whereas confirmatory status was based on additional IgM testing of the index donation and NAT and serology testing of follow-up samples.

RESULTS

From July through October 2003, 2.5 million donations were screened for WNV RNA. Of 877 NAT-reactive donations (screening positivity rate of 3.5 per 10,000 units), 430 (49%) were confirmed positive, whereas 68 (8%) lacking follow-up data remained presumed positive. The sensitivity and positive predictive value of a presumed viremic result relative to final confirmatory status were 92 and 99 percent, respectively. WNV activity was highest in the central plains with prevalence per 10,000 peaking August 1 to 15 in Colorado (67.7) and South Dakota (77.5) and August 16 to 31 in Wyoming (74.1) and North Dakota (102.0).

CONCLUSIONS

WNV screening interdicted many viremic units, thereby reducing transfusion-transmitted infections. This study demonstrates that a national collaborative effort facilitates timely surveillance of blood donor infectious disease prevalence rates.

Analytical and clinical sensitivity of West Nile virus RNA screening and supplemental assays available in 2003

BACKGROUND

Transfusion-transmitted West Nile virus (WNV) infections were first reported in 2002, which led to rapid development of investigational nucleic acid amplification tests (NAT). A study was conducted to evaluate sensitivities of WNV screening and supplemental NAT assays first employed in 2003.

STUDY DESIGN AND METHODS

Twenty-five member-coded panels were distributed to NAT assay manufacturers. Panels included five pedigreed WNV standards (1, 3, 10, 30, and 100 copies/mL), 15 or 16 donor units with very-low-level viremia identified through 2003 screening, and four or five negative control samples. Samples were tested neat in 10 replicates by all assays; for NAT screening assays, 10 replicates were also performed on dilutions consistent with minipool (MP)-NAT. The viral load distribution for 142 MP-NAT yield donations was characterized, relative to the analytical sensitivity of MP-NAT systems.

RESULTS

Analytical sensitivities (50% limits of detection [LoD] based on Poisson model of detection of WNV standards) for screening NAT assays ranged from 3.4 to 29 copies per mL; when diluted consistent with MP pool sizes, the 50 percent LoD of screening NAT assays was reduced to 43 to 309 copies per mL. Analytical sensitivity of supplemental assays ranged from 1.5 to 7.7 copies per mL (50% LoD). Detection of RNA in donor units varied consistent with analytical LoD of assays. Detection of low-level viremia after MP dilutions was particularly compromised for seropositive units, probably reflecting lower viral loads in the postseroconversion phase. Based on the viral load distribution of MP-NAT yield donations (median, 3519 copies/mL; range, < 50-690,000), 13 to 24 percent of units had viral loads below the 50 percent LoD of screening NAT assays run in MP-NAT format.

CONCLUSION

WNV screening and supplemental assays had generally excellent analytical sensitivity, comparable to human immunodeficiency virus-1 and hepatitis C virus NAT assays. The presence of low-level viremic units during epidemic periods and the impact of MP dilutions on sensitivity, however, suggest the need for further improvements in sensitivity as well as a role for targeted individual-donation NAT in epidemic regions.

Le virus West Nile : généralités et implications en transfusion sanguine

West Nile virus (WNV) is an arbovirus (genus Flavivirus, Family Flaviviridae, transmitted to humans by mosquito bite. In most cases (80%), human infection remains asymptomatic. Severe central nervous system complications (encephalitis and meningoencephalitis) are rare. In the Old World, the virus circulation has been demonstrated in Asia, Australia, Africa, Middle East and Europe. Several outbreaks in humans have been described. Following its introduction into North America in 1999, WN virus has been responsible of a large number of human cases in USA and Canada. For the first time, viral transmission by blood products was clearly demonstrated in USA in 2002. In France, the presence of virus has been reported in the Southeastern departments since 1962. In 2003, the occurrence of humans cases at specific geographical foci urged the French National Blood Agency (etablissement francais du sang) to take preventive measures for evaluating the virus transmission risks.