Chronically Infected Patients with Trypanosoma cruzi Parasitemia: Further Support for Screening

Blackburn, Brian
January 2009
Travel Medicine Advisor;Jan2009, Vol. 19 Issue 1, p1
Chagas disease (American trypanosomiasis) is caused by infection with the protozoan parasite Trypanosoma cruzi, and is spread primarily by triatomine insect vectors ("kissing bugs"). Although vector-borne transmission is primarily confined to rural Latin America, other routes of transmission (eg, blood transfusion) are also possible. Untreated infection seems to persist indefinitely, and the estimated lifetime risk of developing cardiac or other sequelae is about 20%-30%. When combined with increasing migration from Latin America, this long-term infection persistence means there is an increasing risk of blood transfusion-associated T. cruzi transmission in non-endemic areas such as the United States; estimates of the number of infected US immigrants range from tens of thousands to more than 100,000. Furthermore, some data indicate that the estimated T. cruzi-seropositivity rate among blood donors in Los Angeles rose between 1996 and 1998. In the United States, the largest contributor to the blood supply (the American Red Cross) began screening blood products for T. cruzi in 2007 with an ELISA-based test that had been FDA approved just months earlier. Recent data suggest one in 4,655 donations to be positive by both ELISA and a confirmatory, second immunologic assay (data were derived from donors in California and Arizona) for T. cruzi. Although hundreds of potentially infective blood products are transfused annually, only five US transfusion-associated cases have been documented to date. This discordance raises the question of whether seropositive persons have patent infection and, thus, the potential to transmit T. cruzi to others through blood transfusion, or simply evidence of prior infection. Leiby et al undertook a study that attempted to confirm that T. cruzi-seropositive donors do have persistent, patent infection by identifying 147 persons who had previously been identified as seropositive for T. cruzi. Fifty-two (35%) of these 147 persons consented to enrollment, and they were asked to provide both epidemiologic data and blood for analysis by T. cruzi-polymerase chain reaction (PCR) and hemoculture testing. Although three samples (drawn six months apart) were requested from all participants, only 17 (33%) of the 52 patients in the study submitted more than a single sample for analysis. Overall, 33 (63%) of the 52 participants had T. cruzi detectable in their blood by PCR; three of the PCR-positive samples were also positive by hemoculture. Of the 11 PCR-positive persons who provided more than one blood sample for testing, eight (73%) were positive on multiple occasions, although most only intermittently (ie, not on every sample tested). Epidemiologic data indicated that 80% were from either Mexico or El Salvador, and the median time since immigration to the United States was 18 years. Eighty-six percent of the cohort reported living in substandard housing during their time in Latin America, and 64% reported seeing triatomine insects at some point in their lives.


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