Approach to diagnosis of congenital Chagas disease

PCR: polymerase chain reaction.
* Pregnant women who warrant screening include those who have lived or spent significant periods of time in areas of Latin America with vector-borne transmission, especially those who lived in houses with adobe walls and/or thatched roofs. (Refer to the UpToDate topic on epidemiology of Chagas disease for further discussion.)
¶ Further follow-up should be arranged for maternal evaluation and treatment for Chagas disease after completion of lactation. In addition, testing for Chagas disease should be pursued for the mother's other children (if any). (Refer to UpToDate topic on diagnosis of Chagas disease for further discussion.)
Δ Positive microscopy in fresh blood or buffy coat is sufficient to make the diagnosis; however, the sensitivity is <30% in a single specimen. The sensitivity of PCR in a single specimen is 65 to 75%. Thus, PCR is often positive despite negative microscopy.
◊ Interpretation of PCR results and threshold for positivity depends on the assay used and the local laboratory threshold. In general, positive PCR results with high parasite load (eg, >100 parasite equivalents per mL, where estimated detection threshold is <1 parasite equivalent per mL) in an experienced laboratory is sufficient to establish the diagnosis. The diagnosis may also be established by two positive PCR results in two separate specimens, regardless of parasite load. Occasionally transiently positive PCR results with low parasite load (usually <50 parasite equivalents per mL) occur in uninfected infants, especially soon after birth. In such cases, a repeat specimen should be tested for microscopy and PCR in 1 to 3 weeks.