Detection of West Nile virus in the Mexican blood supply

BACKGROUND

West Nile virus (WNV) is the etiologic agent of an emerging disease in the Western Hemisphere that can be transmitted to humans by blood transfusion. WNV first appeared in the United States in 1999, in Canada in 2001, and in Mexico in 2002. The aim of this nationwide study was to determine the prevalence of WNV in blood donors in Mexico as a first step in preventing its transfusion-associated transmission.

STUDY DESIGN AND METHODS

In July and August 2004, a total of 3856 fresh plasma specimens collected from each state's center for blood transfusion in 29 of 31 Mexican states were screened with an investigational WNV assay (Procleix,(R) Gen-Probe Inc. and Chiron Corp.), a nucleic acid test based on transcription-mediated amplification (TMA). Reactive specimens were confirmed with a second TMA-based test, the alternative WNV assay (Gen-Probe), and with WNV capture enzyme-linked immunosorbent assays (ELISAs) for detection of immunoglobulin M (IgM) and IgG antibodies. In addition, 3714 frozen plasma samples collected in 2002 and 2003 were similarly tested.

RESULTS

One of 3856 fresh samples from an asymptomatic donor from Chihuahua was reactive by both TMA-based tests and IgM ELISA, suggesting a recently acquired infection. The observed percentage of viremic donors blood donors was 0.03 percent. Results from frozen samples were not included in the prevalence calculation and none were TMA-reactive for WNV.

CONCLUSIONS

WNV is present in the Mexican blood supply and measures should be taken to reduce the risk of transfusion transmission.

Hepatitis C seroprevalence in accepted versus deferred blood-donor candidates evaluated by medical history and self-exclusion form

BACKGROUND

Hepatitis C virus (HCV) represents a viral pandemic that is five times as widespread as human immunodeficiency virus. Blood transfusion posed a major risk of HCV infection in developed countries before 1990, but the introduction of improved blood-screening measures has decreased the risk of transfusion-associated HCV infection, which may now be even lower since the introduction of screening of pooled samples by nucleic acid testing (NAT). Unfortunately, NAT is not affordable in most developing countries. The goal of this work is to assess the usefulness of both screening measures, the medical history, and the self-exclusion form to distinguish between high-risk and low-risk populations of HCV-carrier blood-donor candidates in Mexico.

STUDY DESIGN AND METHODS

From February 2002 to April 2003, 4174 consecutive candidates were enrolled in a prospective, nonrandomized and comparative study. In total, 4158 candidates were included in the analysis and divided in two groups: Group A consisted of 3101 accepted donors and Group B consisted of 1057 deferred donors according to a complete medical history and self-exclusion form. The only exclusion criteria was the lack of a signed consent form to enter the study. All candidates from both groups underwent anti-HCV detection by third-generation enzyme immunoassay (EIA). Those who had either a positive or gray-zone signal-to-cutoff ratio underwent polymerase chain reaction and a second EIA test. If the second EIA test resulted in either a positive or gray-zone signal-to-cutoff ratio, a recombinant immunoblot assay test was performed. The chi-square test was used for statistical analysis, and a p value less than 0.05 was considered significant.

RESULTS

Anti-HCV prevalence by the EIA method was as follows: 0.61 percent for Group A and 1.32 percent for Group B (p = 0.0243); whereas with recombinant immunoblot assay the prevalence was 0.19 percent for Group A and 0.47 percent for Group B (p = 0.1265). When we analyzed the polymerase chain reaction test results, the prevalence in Group A was 0.10 percent (95% confidence interval, 0.089-0.110) and in Group B was 0.47 percent (95% confidence interval, 0.439-0.500) (p = 0.0159).

CONCLUSIONS

The medical history of blood donors in conjunction with serologic screening tests helps to improve blood transfusion safety. This measure is recommended in blood banks of those countries where NAT is still unaffordable.