Should Blood Donors Be Screened for Trypanosomal Infection?
ABSTRACT & COMMENTARY
Synopsis: Serological evidence of infection with Trypanosoma cruzi, which is transmissible by blood transfusion, was present in 0.14% of southern California and Miami blood donors.
Source: Leiby DA, et al. Seroepidemiology of Trypanosoma cruzi, etiologic agent of Chagas’ disease, in U.S. blood donors. J Infect Dis 1997;176:1047-1052.
Leiby and colleagues evaluated the prevalence of serum antibody to Trypanosoma cruzi among blood donors in the United States because of the potential transmissibility of this organism by blood transfusion. All community whole blood donors in American Red Cross regions including Los Angeles and Orange counties, as well as metropolitan Miami, were evaluated during a 14-month period. During that time, 8.24% of 299,397 donors reported, on questioning, that they had spent at least four weeks in Mexico, Central America, or South America and were, therefore, at risk of having been infected with T. cruzi.
Serum from 23,978 "at risk" and 25,587 "not at risk" donors was tested by EIA for antibody to the organism, and those that were repeatedly positive were further evaluated by a confirmatory radioimmunoprecipitation assay (RIPA). False-positive EIAs were so frequent that their positive predictive value was only 32.4%. Of the at-risk group, 33 (0.14%) were RIPA positive, as was one (0.004%) of those "not at risk." Investigation found that this single individual had, in fact, been born in and had lived in El Salvador.
Among the risk factors for seropositivity identified in a case-control study were prolonged duration of residence in an endemic area (all but one having been born in such an area, as well) and lower socioeconomic status, including having lived in "simple housing."
Nine confirmed seropositive donors had donated blood prior to their identification. In a lookback investigation, all 11 recipients of their blood who were tested were found to be negative by EIA.
COMMENT BY STAN DERESINSKI, MD, FACP
It is estimated that there are approximately 50,000 deaths per year in these endemic areas due to Chagas’ disease in the endemic areas among the 16-18 million infected individuals (Kirchhoff LV. N Engl J Med 1993;329:639-644). At the same time, in the last decade, millions of individuals have emigrated from those areas to North America. Leiby and colleagues estimate that at least 2.5% of blood donors in the United States have a geographic risk of exposure to T. cruzi, with much higher prevalences in areas of the country with larger Hispanic populations, such as those studied by them. Furthermore, it appears that time does not heal; transmission may occur from blood donors who left the endemic area more than a decade previously.
Transmission of infection with T. cruzi by transfusion is not uncommon in the endemic areas. In the United States, four such cases, all in immunocompromised hosts who had received at least one unit of platelets, received cells prepared and stored under conditions that may concentrate the organism and favor its survival. Only one of the 11 lookback recipients reported in the paper under review received platelets.
Leiby and associates point out that the upper confidence limit for the risk of transmission of trypanosomiasis by transfusion of seropositive blood, despite the lack of same in 11 of 11 cases, is 28%. This is within the range of risk reported in the endemic areas.
Leiby and colleagues conclude that a strategy of testing only donors who report geographic risk is not likely to be effective and that the most effective strategy may be to test all donors for antibody to T. cruzi.
Which of the following is correct?
a. An individual infected with T. cruzi becomes non-infectious within five years in the absence of reinfection.
b. Areas endemic for T. cruzi include South America and Africa.
c. Although theoretically possible, transmission of T. cruzi infection by blood transfusion has not been observed in the United States.
d. It is estimated that as many as 18 million people living in endemic areas are infected with the organism that causes Chagas’ disease.
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