Rapid Diagnostic Tests Sensitive, Specific for Chagas Disease

By Anne Harding

December 27, 2019

NEW YORK (Reuters Health) - Rapid diagnostic tests (RDTs) can be used to diagnose chronic Chagas disease with high sensitivity and specificity, a new field implementation study shows.

"In a region highly endemic for Chagas disease as it is the Bolivian Chaco, the combined use of two Rapid Diagnostic Tests managed to work with similar efficiency to currently used algorithm for the detection of chronic Chagas disease," Dr. Julio Alonso-Padilla of the Barcelona Institute for Global Health at the University of Barcelona told Reuters Health in an email.

"This is great news as it has shown in the field that the application of easy-to-use RDTs could eventually substitute (for) the more complicated and equipment-demanding ELISAs in the process of granting access to diagnosis of this neglected disease," he added.

Chagas disease does not typically manifest symptoms until infection becomes chronic, and is usually diagnosed at this stage, Dr. Alonso-Padilla and his team note in their report in PLOS Neglected Tropical Diseases. While acute infection responds well to treatment, they write, about 40% of those with chronic infection will develop serious damage to cardiac and gut tissues that can be fatal if left untreated.

"Despite the advantages of treatment, it is estimated that less than 1% of those infected eventually get access to it, due to a series of factors amongst which overarches the lack of a timely diagnosis," they add.

Many of the regions where Chagas disease is endemic don't have the infrastructure to support conventional serological testing, the authors note. Previously, they proposed using two RDTs simultaneously for diagnosing Chagas disease in remote regions without lab access. In the new report, the authors evaluated the tests in 14 field screening campaigns around the towns of Yacuiba and Villa Montes, testing samples from 685 volunteers who had not received treatment for Chagas disease.

The authors used the Chagas Stat-Pak (CSP; Chembio Inc., Medford, USA) and Chagas Detect Plus (CDP; InBIOS International Inc., Seattle) RDTs. If these two RDTs were discordant, they followed up with the WL-Check RDT kit (Wiener Laboratorios, Buenos Aires, Argentina). The three tests were performed simultaneously using blood gathered by finger prick.

A total of 304 volunteers were positive with both RDTs, and 334 had negative results with both. Using the gold-standard algorithm based on the agreement of two ELISA tests, there were 297 confirmed positives and 7 false positives, 5 false negatives and 329 true negatives.

For the 47 with discordant results, WNCheck found 8 were positive and 39 were negative. Confirmation with ELISA testing identified two false negatives.

Results agreement for CSP was 97.5% with an 0.95 kappa value. For CDP, the level of agreement was 92.1% and kappa value was 0.84.

Compared to a combination of up to three ELISAs, the RDTs algorithm with up to three tests was 97.7% sensitive and 96.1% specific, with a positive predictive value of 95.2% and a negative predictive value of 98.1%.

Future research is needed to evaluate the performance of the RDTs in areas with a lower seroprevalence of Chagas disease, and in areas where patients may also have leishmaniasis, Dr. Alonso-Padilla said.

"Other challenges would be to evaluate RDTs in other geographic areas where different T. cruzi strains are predominant," he added.

SOURCE: http://bit.ly/2PTrIj7 PLOS Neglected Tropical Diseases, online December 20, 2019.