this study was approved by institutional review boards at baylor college of medicine ( houston , tx , usa ) , the gulf coast regional blood center ( houston ) , and the south texas tissue and blood center ( san antonio , tx , usa ) .
blood donors residing in the greater san antonio , texas , area who had t. cruzi antibodies detected by prism chemiluminescent immunoassay ( abbott laboratories , chicago , il , usa ) or ortho t. cruzi elisa ( ortho - clinical diagnostics inc . , raritan , nj , usa ) , and a positive result for a radioimmune precipitation assay ( quest diagnostic laboratories , madison , nj , usa ) or an esa chagas test ( abbott laboratories ) during january 1 , 2008december 31 , 2014 , were invited to participate in the study .
persons previously enrolled in a houston - based t. cruzi  seropositive blood donor project were not eligible for this study ( 8) . letters in english and spanish were sent to donors who had t. cruzi antibodies by the blood centers for this study . those who agreed to participate provided informed consent .
we performed 3 procedures : 1 ) blood collection for additional serologic screening , 2 ) structured interview to assess potential transmission sources and health , and 3 ) 12-lead resting electrocardiogram ( ecg ) ( 8) .
we defined a case of t. cruzi infection if donor screening test results and > 2 serologic test results were positive .
likely autochthonous t. cruzi infection was defined in a case - patient who had no major travel to a latin american country ( lasting > 2 weeks or that included an overnight stay in a rural region ) , not having been born in latin america , and not having a mother born in latin america ( 4,810 ) . congenital transmission from a maternal grandmother ( 2 contiguous congenital infections ) can not be ruled out with this case definition but is unlikely given the low risk for congenital transmission ( 7 ) .
demographic information , likely autochthonous transmission , and concurrent conditions were determined through case - patient interview .
ecg , electrocardiogam ; ind , indeterminate ; + , positive ;  , negative .
donors listed as showing autochthonous transmission ( donors 1214 ) reported living in mexico or chile . 
esa , chagas test ( abbott laboratories , chicago , il , usa ) ; ortho , t. cruzi elisa ( ortho - clinical diagnostics inc . , raritan , nj , usa ) ; prism , chemiluminescent immunoassay ( abbott laboratories ) ; ripa , radioimmune precipitation assay ( quest diagnostic laboratories , madison , nj , usa ) .   dpp , dual path platform immunochromatographic confirmation assay ( chembio , medford , ny , usa ) ; eia , chagatest recombinant v3.0 enzyme inmmunoassay ( wiener , rosario , argentina ) ; hemagen ; chagas eia kit ( hemagen diagnostics , inc . ,
columbia , md , usa ) ; stat - pak , chagas immunochromatographic sssay ( chembio , medford , ny , usa ) ; tesa , trypomastigote excreted or secreted antigen immunoblot ( biomrieux , marcy letoile , france ) .
hemagen , stat - pak , and dpp were performed at baylor college of medicine , ( houston , tx , usa ) , and eia and tesa were performed at the centers for disease control and prevention ( atlanta , ga , usa ) . 
results were determined from readout of a resting 12-lead ecg and interpreted by a board - certified cardiologist .
av , atrioventricular ; lad , left axis deviation ; lvh , left ventricular hypertrophy ; rbbb , right bundle branch block . for persons who donated blood in the greater san antonio area during the study period , we found that 61/256,801 donors had positive serologic results for t. cruzi infection ( 1/4,200 donors had positive serologic results for t. cruzi infection by 2 assays ) .
seventeen ( 28% ) of these were enrolled in the study ; additional serologic testing confirmed that 14 had antibodies against t. cruzi when the study began ( table 1 ) .
these persons had a mean age of 47 years ( range 1983 years ) ; 50% were hispanic , 50% were non - hispanic white , and 50% were men . for 3 persons whose blood donor testing results
were not confirmed by further serologic testing , 2 were non - hispanic and 1 was hispanic ( 2 women and 1 man ) ; mean age was 51 years . because of the blinded nature of study recruitment , we can not identify demographic data for persons who received the letter and chose not to participate .
likely autochthonous transmission of t. cruzi was suspected for 11 ( 79% ) of 14 persons , as defined by study criteria .
these 11 persons had a mean age of 50 years ; 7 were non - hispanic whites , and 6 were men .
remaining data presented will concern only the 11 newly identified persons with likely autochthonous infections .
a structured interview adapted from a questionnaire used by the centers for disease control and prevention ( atlanta , ga , usa ) , the american red cross ( washington , dc , usa ) , and blood systems , inc .
( scottsdale , az , usa ) , was used to identify risk factors for t. cruzi infection ( 4 ) .
because of the lifelong nature of infection and antibody - based diagnostics used , a specific time of infection could not be established for each case - patient .
most ( 91% ) case - patients with likely autochthonous infection reported a history of living in a rural community ( figure ) .
residence in rural communities could pose a risk for t. cruzi transmission because this setting might lead to close proximity with sylvatic transmission cycles involving the vector and infected animals ( 11 ) .
current and previous residences of persons with likely autochthonous infection with trypanosoma cruzi , south central texas , usa , including 11 autochthonous donors with current residence and birthplace .
previous residences in texas were chosen if the case - patient reported living in the location > 5 years .
although recreational activities or occupations associated with outdoor exposure were reported among our cohort , we obtained evidence suggesting that opportunities for transmission might be occurring near homes in rural communities ( table 2 ) .
specifically , patients with likely autochthonous infections reported seeing the vector around their current or previous residence ( 36% ) , and had animal housing near their homes ( 73% ) .
an extensive history of outdoor recreational activities of hunting and camping , which has been suggested as a high - risk activity for t. cruzi transmission in the southern united states , was less common then expected ( 36% ) ( 8,12 ) .
two of 11 case - patients reported agricultural jobs and staying in substandard housing during the harvest season , thereby introducing the potential for disease transmission from triatomines in the home .
no risk ( 0 ) was defined as not living in a rural area and having no history of outdoor occupation or recreational activities .
low risk ( + ) was defined as ever living in a rural area , having an outdoor occupation , or engaging in hunting or camping in an area with known triatomine activity .
moderate risk ( + + ) was defined as , in addition to low - risk activities , an extensive history of these activities ( > 1 y ) , or having slept in a tent in a rural part of texas .
high risk ( + + + ) was defined as , in addition to moderate - risk activities , reporting 1 of the following : reported seeing triatomines , had collective animal housing around the property , or lived or slept in substandard housing .
five case - patients reported a lack of knowledge of chagas disease by their primary care physicians .
some case - patients were provided with misinformation , reporting having been told that their screening test result must be false positive because they had no travel history .
furthermore , only 2 case - patients were offered treatment before enrollment in the study .
one case - patient reported that , despite seeking treatment for > 1 year , he was unable to find a physician able and willing to help .
this finding is particularly problematic given that a large proportion ( 6 of 11 ) of this cohort had abnormal ecg readings possibly attributable to chagasic cardiac disease .
although precise cardiac etiologies could not be determined , prevalence of ecg abnormalities was higher than that for population - based studies ( 13,14 ) ; common findings included atrioventricular block and left axis deviation ( table 1 ) .
a previous report also highlighted the same lack of physician awareness of chagas disease in texas , despite patients having positive serologic screening results and cardiac manifestations ( 8) .
given the low level of participation of seropositive blood donors , results of this study are limited to persons who participated and might not represent the larger texas blood donor population or general population . also , because a 7-year span separated initial screening and enrollment in this study , it is difficult to identify why 3 persons who were initially positive by blood bank screening had discordant results during the study . at follow - up , participating persons were tested with available centers for disease control and prevention assays , food and drug administration  approved screening , or supplemental tests .
our study adds 11 cases of likely domestically acquired t. cruzi infection to the increasing body of evidence for autochthonous chagas disease transmission in the southern united states .
combined with previous studies indicating a high rate of t. cruzi infection in triatomine vectors and mammalian reservoirs in this area , our study shows that south central texas could be a focal point for endemic disease transmission ( 7,15 ) .
we also identified a major knowledge gap for chagas disease , which highlights the need for enhanced public health campaigns targeting clinicians and the general population in south central texas .
 chagas disease , caused by trypanosoma cruzi , is a major neglected tropical disease affecting the americas . 
 the epidemiology of this disease in the united states is incomplete . 
 we report evidence of likely autochthonous vectorborne transmission of t. cruzi and health outcomes in t. cruzi  seropositive blood donors in south central texas , usa . 
The Study
Conclusions