Enhanced classification of Chagas serologic results and epidemiologic characteristics of seropositive donors at three large blood centers in Brazil.
BACKGROUND
A major problem in Chagas disease donor screening is the high frequency of samples with inconclusive results. The objective of this study was to describe patterns of serologic results among donors to the three Brazilian REDS-II blood centers and correlate with epidemiologic characteristics.


METHODS
The centers screened donor samples with one Trypanosoma cruzi lysate enzyme immunoassay (EIA). EIA-reactive samples were tested with a second lysate EIA, a recombinant-antigen based EIA, and an immunfluorescence assay. Based on the serologic results, samples were classified as confirmed positive (CP), probable positive (PP), possible other parasitic infection (POPI), and false positive (FP).


RESULTS
In 2007 to 2008, a total of 877 of 615,433 donations were discarded due to Chagas assay reactivity. The prevalences (95% confidence intervals [CIs]) among first-time donors for CP, PP, POPI, and FP patterns were 114 (99-129), 26 (19-34), 10 (5-14), and 96 (82-110) per 100,000 donations, respectively. CP and PP had similar patterns of prevalence when analyzed by age, sex, education, and location, suggesting that PP cases represent true T. cruzi infections; in contrast the demographics of donors with POPI were distinct and likely unrelated to Chagas disease. No CP cases were detected among 218,514 repeat donors followed for a total of 718,187 person-years.


CONCLUSIONS
We have proposed a classification algorithm that may have practical importance for donor counseling and epidemiologic analyses of T. cruzi-seroreactive donors. The absence of incident T. cruzi infections is reassuring with respect to risk of window phase infections within Brazil and travel-related infections in nonendemic countries such as the United States.
Sabino
Ester C
EC
Pró-Sangue Foundation and the University of São Paulo, São Paulo, Brazil. sabinoec@gmail.com
Salles
Nanci A
NA
Sarr
Moussa
M
Barreto
Angela M
AM
Oikawa
Marcio
M
Oliveira
Cláudia D
CD
Leao
Silvana C
SC
Carneiro-Proietti
Anna B
AB
Custer
Brian
B
Busch
Michael P
MP
D000328:Adult; D000465:Algorithms; D001771:Blood Banks / Q000592:standards / Q000706:statistics & numerical data*; D001782:Blood Donors / Q000145:classification* / Q000706:statistics & numerical data*; D001938:Brazil / Q000453:epidemiology; D014355:Chagas Disease / Q000097:blood / Q000175:diagnosis* / Q000453:epidemiology* / Q000276:immunology; D046148:Donor Selection / Q000379:methods; D005260:Female; D006801:Humans; D008297:Male; D016036:Seroepidemiologic Studies; D012698:Serologic Tests / Q000145:classification / Q000379:methods / Q000592:standards; D014349:Trypanosoma cruzi / Q000276:immunology; D055815:Young Adult; D000094902:Blood Banking / Q000379:methods