The IgM-SAPA-test for the early diagnosis of congenital Chagas disease in the time of the elimination goal of mother-to-child transmission.

BACKGROUND Diagnosis of congenital Chagas disease (CChD) in most endemic areas is based on low-sensitive microscopy at birth and 9-month IgG, which has poor adherence. We aim to evaluate the accuracy of the IgM-Shed Acute Phase Antigen (IgM-SAPA) test in the diagnosis of CChD at birth. METHODS Two cohort studies (training and validation cohorts) were conducted in three hospitals in the department of Santa Cruz, Bolivia. Pregnant women were screened for Chagas disease, and all infants born to seropositive mothers were followed for up to nine months to diagnose CChD. A composite reference standard was used to determine congenital infection and was based on the parallel use of microscopy, qPCR, and IgM-TESA-blot (Trypomastigote Excreted-Secreted Antigens) at birth and/or 1-month, and/or the detection of anti-Trypanosomacruzi IgG at 6- or 9- months. The diagnostic accuracy of the IgM-SAPA-test was calculated at birth against the composite reference standard. RESULTS Adherence to the 6- or 9-month follow-up ranged from 43.8% to 59.7%. Most cases of CChD (training and validation cohort: 76.5% and 83.7%, respectively) were detected during the first month of life using the combination of microscopy, qPCR and/or IgM-TESA-blot. Results from the validation cohort showed that when only one infant sample obtained at birth was evaluated, the qPCR and the IgM-SAPA-test have similar accuracy (sensitivity: range 79.1% to 97.1%, and 76.7% to 94.3%, respectively, and specificity: 99.5%, and 92.6%, respectively). CONCLUSIONS The IgM-SAPA-test has the potential to be implemented as an early diagnostic tool in areas that currently rely only on microscopy.