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Testing for Trypanosoma cruzi in the U.S. Blood Supply

Based on data from California blood banks, testing all donors — or screening and then testing — was cost-effective; the preferred strategy would vary with site-specific risk.

Trypanosoma cruzi, which causes Chagas disease, can be transmitted via transfused blood products. By some estimates, more than half a million immigrants (documented and undocumented) from Latin America living in the U.S. are infected with this protozoan. An ELISA test to detect T. cruzi antibodies has been licensed by the FDA, but testing donated blood is not mandatory. To determine the best approach for U.S. blood banks, researchers assessed three strategies: serologic testing of all donations; verbal screening, with serologic testing of donations from persons positive on such screening; and no screening or testing.

The investigators surveyed 2029 blood donors at five California sites to determine risk for Chagas disease. Using a semi-Markov model, they compared the cost-effectiveness of the three strategies, taking into account factors such as location of exposure, donor age, test sensitivity and specificity, and costs of early and late consequences of infection.

In the donor population studied, 30% (range, 16% to 37%) had a positive verbal screening for potential risk. Either testing all donors or verbally screening first and then testing selectively was cost-effective compared with not testing at all. The preferred strategy will vary by geographic region and by the percentage of the population at high risk for infection. In the population studied, U.S. census estimates of the Hispanic population did not predict the percentages of high- and low-risk blood donors.

Comment: The authors acknowledge limitations of a study based on only five blood banks, but they provide a framework that might be useful to other institutions developing testing policies. They assessed only single-unit testing, whereas pooled-blood analysis has been cost-effective in testing for some pathogens. They also did not consider repeat donors in their model. The issue of testing blood is not trivial: In the U.S., the average number of annual donations is nearly 15 million.

— Mary E. Wilson, MD

Published in Journal Watch Infectious Diseases July 23, 2008

Citation(s):

Wilson LS et al. Cost-effectiveness of implementation methods for ELISA serology testing of Trypanosoma cruzi in California blood banks. Am J Trop Med Hyg 2008 Jul; 79:53.

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