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 US$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. Screening all blood donations in all States to avoid transmission to blood transfusion recipients is not cost-effective. Background: West Nile virus (WNV) was first isolated from a sick woman in the West Nile region of Uganda in 1937. The virus has subsequently been found to be widespread in Africa and Eurasia, and sporadic outbreaks have been reported throughout these regions. WNV was first detected in the US in 1999, in a sick woman in New York. The disease has since spread to most states in the continental US, making thousands of people ill and causing several hundred deaths. Wild birds are the principal host of WNV, and the virus is transmitted to humans mainly by mosquitoes that bite both birds and humans. Most of the people who get infected by a mosquito bite do not get sick at all, but about 20% develop a flu-like illness. In a small number of cases—especially among the elderly and people with a weakened immune system—the infection spreads to the nervous system and can cause death or long-term disability. Like other blood-borne diseases, WNV can be transferred by blood transfusion with contaminated blood. Such cases have occurred in the US and have killed few people. Why Was this Study Done?: WNV can be detected in blood samples by recently developed and approved tests. These tests detect most, but not all, cases of contamination with the virus. This means the WNV deaths resulting from transfusion of contaminated blood are potentially avoidable by screening donated blood. As a consequence, the US Food and Drug Administration (FDA) has mandated screening of donated blood samples. However, the FDA has not prescribed specific screening strategies, and the decision on how to best screen blood samples has been left to the individual states and the blood-collection agencies. The researchers who carried out this study wanted to determine which screening strategies would be cost-effective—that is, which strategies would prevent infections through contaminated blood for a reasonable price. In an ideal world, cost would not matter when it comes to protecting human life and health, but in reality there is limited money available for public health measures. Studies such as this one are therefore essential to help politicians decide how to spend the money. What Did the Researchers Do and Find?: They calculated the costs of screening and the number of prevented infections through blood transfusion for a number of different scenarios. They found that in states with low WNV infection rates, the risk of an infected person donating blood was so low that screening was unlikely to prevent cases of serious illness from WNV, despite substantial costs. In states where WNV is common, screening throughout the year is likely to prevent cases of serious illness, but at a substantial cost. In states where WNV is common, screening blood only from May to the end of October (the months when mosquitoes are around and people get infected from them), however, was as effective at identifying contaminated blood samples as screening throughout the year. One way to reduce costs substantially was to create a separate blood pool that is reserved for transfusions to people with a weakened immune system and to screen only those samples. Because those are the people most at risk for severe WNV illness, this strategy would still prevent most of those cases. What Do These Findings Mean?: It is not clear whether the current policy to screen all blood samples in all states makes sense from a health economy point of view. Restricting screening to states where WNV is common and to samples designated for people at higher risk for severe WNV illness would reduce costs significantly without putting the recipients of blood transfusions at a substantially higher risk of serious illness caused by WNV. Where Can I Get More Information Online?: The following Web sites provide information on WNV.