Chagas disease, caused by the parasite Trypanosoma cruzi,
is a global phenomenon, but the highest burden is concentrated in low-income parts of South America. While there are effective tests for detecting Chagas disease commercially available, their use isn’t practical in highly endemic regions due to poorly equipped laboratories.
Rapid diagnostic tests provide a potential alternative for diagnosis of Chagas disease in the context of material constraints. A new field study
published in PLOS Neglected Tropical Diseases
evaluated the use of these tests to detect chronic Trypanosoma cruzi
infections in the Chaco region of Bolivia, with results supporting the use of rapid diagnostic tests.
To compare the performance of rapid diagnostic tests with enzyme-linked immunosorbent assays (ELISAs), rapid diagnostic tests were introduced to field screening campaigns performed in communities surrounding the cities of Villa Montes and Yacuiba.
Investigators compared an alternative algorithm based on a combination of standard ELISAs with rapid diagnostic tests, with a third test available in case of discordance.
Field teams consisted of an operator—who was responsible for the administration and interpretation of rapid diagnostic tests—and a support team to help inform and communicate with the study participants.
Enrollment was offered to individuals above 1 year of age who had not been treated for Chagas disease in the past. A total of 685 individuals voluntarily participated in the study. Sampling was done between April and August 2018. Investigators reported that the number of people who could be screened per day ranged from 18 to 60.
Subjects were seen in a single visit which included informed consent around the study and performance of rapid diagnostic tests from finger-prick blood samples. A larger volume of blood (approximately 3 ml) was also extracted for the comparison ELISA tests to be conducted in hospital laboratories.
Agreement between the rapid diagnostic tests was established for 638 out of 685 tests (93.1%). Compared to the ELISAs algorithm, use of the rapid diagnostic tests provided a specificity of 96.1% and sensitivity of 97.7%. Agreement between the 2 main ELISAs was slightly higher at 96.1%, but investigators considered rapid diagnostic tests to have high agreement regardless.
When results were discordant among the 2 main rapid diagnostic tests, a third rapid diagnostic test called WL-Check resolved 47 cases, 39 of which were determined to be negative and 8 positives.
In total, 304 out of 685 study participants were described as positive and 381 were described as negative. This indicates overall prevalence of Chagas disease in the population under study is 44.4%.
“Even though further studies are yet required to address the use of RDTs [rapid diagnostic tests] in areas with lower prevalence of T cruzi
and/or co-circulation of closely related pathogens, the results from this work encourage the use of RDTs as an alternative to conventional serological methods in the Bolivian Chaco and other areas with similar epidemiological characteristics,” study authors wrote.
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