Highly endemic regions for Chagas do not have sufficiently equipped laboratories. A new study confirms how joining two rapid tests could facilitate the diagnosis of chronically infected people.
The combined use of two rapid diagnostic tests, which already exist in the market, is capable of diagnosing chronic Chagas with high precision and specificity in mobile campaigns, according to the results of a study funded by the Inter-American Development Bank (IDB) and led by the Global Health Institute of Barcelona (ISGlobal), in collaboration with the CEADES Foundation and the Mundo Sano (Healthy World) Foundation.
The observed performance would allow us to rely on these diagnostic tests in highly endemic regions that do not have sufficiently equipped laboratories. The acute phase of Trypanosoma cruzi infection (the causative agent of chagas) is usually asymptomatic, so it goes unnoticed. Therefore, the diagnosis is usually made in the chronic phase of the disease, when symptoms appear.
Conventional serological tests to diagnose infection (ELISAs) are impractical in regions that do not have equipped laboratories. In contrast, rapid diagnostic tests are easy to use, do not need a cold chain, and require very small amounts of blood.
In an earlier study, the research team had already proposed the combined use of rapid tests as an alternative to serological techniques for the diagnosis of Chagas. “In this research, we take the tests into the field,” explains Julio Alonso-Padilla, researcher at ISGlobal and coordinator of the study, “and we tested their effectiveness, used by mobile teams in diagnostic campaigns.”
Almost complete sensitivity
The research team used 685 samples obtained in the Chaco region (Bolivia), to compare the results of both rapid tests combined and separately, with standard serological tests performed in the laboratory.
They found that the combined use of the tests had a sensitivity (i.e. the ability to detect positive cases) of 97% and a specificity (i.e. the ability to discern negative cases) of 96.1%, compared to the standard algorithm (based on ELISAs).
The results, published in the journal PLOS NTDs, indicated a high prevalence of infection in the region: 44% of analyzed samples were positive. “The results of this study support the use of rapid diagnostic tests as an alternative to conventional serological methods in the Chaco and other regions of high endemicity,” said Julio Alonso-Padilla.