Rapid Tests Conclusively Diagnose Chagas Disease
By Labmedica International staff writers
Posted on 19 Apr 2017
Image: The Chagas Stat-Pak rapid test for the diagnosis of Chagas disease (Photo courtesy of Chembio).
Chagas disease is caused by infection with the Trypanosoma cruzi that are generally transmitted by triatomine vectors that are endemic to the Americas. It affects several million people and severe cardiac and/or digestive complications occur in about 30% of the chronically infected patients.
In recent decades, population movements from endemic to non-endemic regions and the chance of vector-independent transmission have globalized the disease impact to non-endemic countries like Spain. The acute stage of the disease is mostly asymptomatic and infection goes undiagnosed. In the chronic phase direct parasite detection is hampered due to its concealed presence and diagnosis is achieved by serological methods.
Scientists working with those at the Barcelona Institute for Global Health carried out a prospective study and took 342 blood samples from 223 women and 119 men living in an endemic region of Bolivia. Sampling was made between March and May 2014. The study was a double-blind with three different observers involved: two for each of the rapid diagnostic test (RDT), and a third one for the conventional serological tests (indirect hemagglutination assay (IHA), enzyme linked immunosorbent assays (ELISA), based on lysate antigen, and ELISA based on recombinant antigen.
The team used serodiagnosis, first by rapid screening with the RDT Chagas Stat-Pak. A second RDT, Chagas Detect Plus was also used in parallel. In order to qualify a rapidly diagnosed positive patient for treatment, conventional serological confirmation is obligatory. The ELISA tests were from Wiener Lab and included the parasite lysate-based ELISA.
The performance of CST and CDP was identical. The comparison with the conventional serology results yielded exactly the same results, either evaluating them individually or as a duo. Their reported sensitivity was 100% whereas specificity was 99.3%. RDTs positive predictive value was 99.5%, and their negative predictive value was 100%. In comparison with the three conventional serological tests, each RDT detected the same single false positive patient that was shown to be negative in all three conventional serology tests.
The authors concluded that their study validates the use of the CST and CDP diagnostic duo to reduce response time to patients and the logistic resources currently needed to elaborate a confirmed Chagas disease diagnosis. Therefore, they encourage considering the implementation of both RDTs with whole blood as sample to provide fast, reliable and definite diagnosis of Chagas disease in distant settings. The study was published on April 3, 2017, in the journal Public Library of Science Neglected Tropical Diseases.