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Blood Donor Screening for Chagas Disease
Abstract & Commentary
By Mary-Louise Scully, MD
Sansum-Santa Barbara Medical Foundation Clinic, Santa Barbara, CA.
Dr. Scully reports no financial relationship relevant to this field of study.
Synopsis: A newly approved serologic assay for detecting Trypanosoma cruzi infection opens the door for universal screening of blood donations to prevent transfusion-transmitted Chagas disease.
Source: CDC. Blood Donor Screening for Chagas Disease- United States, 2006-2007. MMWR Morb Mortal Wkly Rep. 2007;56:141-143.
During August 2006-January 2007 the American Red Cross conducted a clinical trial to evaluate an investigational assay for detecting Trypanosoma cruzi infection in blood donations. 148,969 blood samples from 3 collection centers (Los Angeles, CA; Oakland, CA; and Tucson, AZ) were screened using an enzyme-linked immunosorbent assay (ELISA) that uses epimastigote lysate antigens to detect antibodies to T. cruzi in serum and plasma. A total of 63 specimens from 61 donors were repeatedly reactive for T. cruzi antibodies. Of the 63 positive specimens, 50 donors (79%) were from the Los Angeles collection center, 14% from Oakland, and 6% from Tucson. Repeatedly reactive specimens were further tested using a radioimmunoprecipitation assay (RIPA): those with positive RIPA results were considered confirmed positives. Of these 63 repeatedly reactive specimens, 32 (51%) donations (approximately one in 4,655) were confirmed positive with RIPA testing, and 31 (49%) were considered negative.
On December 13, 2006, the FDA licensed the new T. cruzi ELISA Test System to screen blood donors in the United States. The assay is also labeled for use on serum and plasma samples from living cell and tissue donors and from heart-beating organ donors but is not approved for general clinical diagnosis. Use of the test by blood centers is not yet mandatory but the American Red Cross and Blood Systems, Inc. began screening all blood donations for T. cruzi on January 27, 2007. These 2 blood collection organizations account for about 65% of the U.S. blood supply. Also, the AABB (formerly known as the American Association of Blood Banks) recommends that all components from blood donations that are repeatedly reactive by the ELISA test be quarantined and removed from distribution. In addition, confirmed positive donors should be deferred from making any further blood donations and testing offered to at-risk family members who have also had a history of exposure to T. cruzi vectors in an endemic area.
Chagas disease is named after Carlos Chagas, a Brazilian physician who discovered and described the disease in 1909 while working at the Oswaldo Cruz Institute in Rio de Janeiro. The parasite, T. cruzi, is transmitted by triatomine insects (ie, kissing bugs) that are found only in the Americas; hence Chagas disease is also known as American trypanosomiasis. Although acute infection can result in mild symptoms such as fever, lymphadenopathy, headache, fatigue, or a swelling (chagoma) at the site of parasite entry, the infected patient is more often asymptomatic. It is estimated that the majority of the 11 million people in Mexico, Central America, and South America with Chagas disease are unaware they have the infection.
If early infections are not treated, Chagas patients will have low-level, intermittent, often asymptomatic parasitemia during what is referred to as the chronic indeterminate phase. However, an estimated thirty percent of infected patients will develop chronic symptomatic Chagas disease with potentially lethal cardiomyopathy or megasyndromes, such as megaeosophagus or megacolon. Treatment options are limited, but early infection should be treated with either benznidazole, which is not available in the United States, or nifurtimox, which is available from the CDC under an investigational new drug protocol. There is increasing evidence to suggest that treatment of persons with chronic infection may result in seroreversion and prevent progression of cardiac morbidity.1
Since even asymptomatic Chagas patients have intermittent low-level parasitemia, they remain potentially infectious. Seven cases of transfusion-associated transmission of T. cruzi have been documented in the United States and Canada, and 3 recent cases of transmission of T. cruzi through organ transplantation have been reported.2 Since T. cruzi parasitemia is intermittent, the nucleic acid testing method that is used for other pathogen screening is less effective than serology testing. The parasite can survive irradiation of blood products, and even leukoreduction fails to remove all T. cruzi parasites. With an estimated 50,000-100,000 T. cruzi- infected immigrants residing in the United States the approval of this new assay now makes it possible to move toward universal screening of blood and tissue donors.
Available data on the performance of the new assay suggest high sensitivity (98.9%) and specificity (98.2 to 99.9%) in high-risk populations.3 However, in areas of lower disease prevalence a greater number of false positives can be expected. Since positive donors will be informed of the results and deferred from further donation, patients will look to their health care providers to identify true positives using further diagnostic testing (eg, diagnostic ELISA tests, immunofluorescence assay, or indirect hemagglutination), clinical evaluation, and exposure risk. In anticipation of questions likely to emerge from this new screening, the CDC released a fact sheet for patients and health care providers on February 6, 2007. It is available at www.cdc.gov.