Use of rapid diagnostic tests (RDTs) for conclusive diagnosis of chronic Chagas disease – field implementation in the Bolivian Chaco region

Chagas disease, caused by the parasite Trypanosoma cruzi, is the neglected tropical disease with a highest burden in Latin America. Its acute stage is mostly asymptomatic and goes unnoticed. Symptoms appear at the chronic stage, which is when diagnosis is usually made. This is based on the agreement of two conventional serological tests such as Enzyme-Linked Immunosorbent Assays (ELISAs). There are commercial kits with good sensitivity and specificity but their use is impractical in many highly endemic regions with poorly equipped laboratories. Luckily, several rapid diagnostic tests (RDTs) are available for the detection of anti-T. cruzi immunoglobulins. They are easy to operate, require no cold storage, provide fast turnaround of results, and some can work with a tiny volume of whole blood as sample. With the aim to field validate their use we compared an alternative algorithm based on a combination of RDTs with the standard based on ELISAs. In both cases a third test was available in case of discordance. RDTs were implemented by mobile teams in field campaigns to detect chronic T. cruzi-infections in the Chaco region of Bolivia. ELISAs were made in the reference laboratories located in the main hospitals of Yacuiba and Villa Montes, two major cities of the region. We enrolled 685 subjects who voluntarily participated in the study and had not been treated against the disease before. The agreement between the two main RDTs was 93.1% (638/685) (kappa index = 0.86; CI 95% 0.83–0.90). In comparison to the ELISAs algorithm, the combined use of the RDTs provided a sensitivity of 97.7% and a specificity of 96.1%. These results support the use of RDTs for the diagnosis of chronic Chagas disease in the studied region, and encourage their evaluation in other regions of Bolivia and other endemic countries.Author summary: Chagas disease is caused by the parasite Trypanosoma cruzi. It affects ~7 million people worldwide, exerting its highest impact in Latin America. The acute stage of the infection is generally asymptomatic and goes undiagnosed and untreated. It is in the long lasting chronic stage that the life-threatening heart and/or gut tissue disruptions may occur. Then diagnosis is performed by serological detection of T. cruzi-specific immunoglobulins in the patients´ sera, usually upon suspicion of the clinical symptomatology. Such diagnosis may arrive too late for those with advanced tissue damage as there are evidences indicating that the treatment might be ineffective for them. It is thus of huge importance to provide an early diagnosis to get access to treatment. But the use of current conventional serological tools is not possible in many highly endemic regions distant from equipped reference laboratories. Herein we evaluate an alternative algorithm for the conclusive diagnosis of chronic Chagas disease based on the use of rapid diagnostic tests (RDTs) in a field study made in the Chaco region of Bolivia. Comparison of the RDTs performance with that of the ELISAs “gold-standard” yielded a sensitivity of 97.7% and a specificity of 96.1%. These values justify a wider use of the RDTs in the region under study, and encourage their evaluation in other regions of Bolivia and other endemic countries.