Molecular versus conventional diagnosis of intestinal parasitoses

Objectives: A field comparison in the period 2003–2010 between conventional and molecular methods for the diagnosis of infection by Entamoeba histolytica, E. dispar, Giardia intestinalis, Dientamoeba fragilis and Cryptosporidium spp. is reported analysing faecal samples from patients with gastro-intestinal signs and symptoms related to a clinical suspicion of intestinal parasitoses.Methods: Two real-time PCR assays for the differentiation of E. histolytica and E. dispar and for the detection of D. fragilis, respectively, in faecal specimens were evaluated in comparison with microscopy and culture. Two real-time PCR assays for the detection of G. intestinalis and Cryptosporidium spp., respectively, were evaluated in comparison with the combination of microscopy, an immunocromatographic assay and an immunofluorescence assay. Results: Conventional assays had a sensitivity of 88.4% for giardiasis, 43.5% for dientamoebiasis, 92.3% for cryptosporidiosis, 41.7% for amoebiasis and a diagnostic specificity of 100% in all cases, whereas molecular assays had 100% sensitivity and specificity in all cases. G. intestinalis. On a total of 422 patients, 112 cases of giardiasis were diagnosed by real-time PCR; only 99 cases were detected by microscopy and/or antigen detection traducing in 13 missed diagnosis. D. fragilis. On a total of 527 patients, 108 cases of dientamoebiasis were diagnosed by real-time PCR; only 47 cases were detected by microscopy and/or cultivation traducing in 61 missed diagnosis. Cryptosporidium spp. On a total of 552 patients, 13 cases of cryptosporidiosis were diagnosed by real-time PCR; only 12 cases were detected by microscopy and/or antigen detection traducing in 1 missed diagnosis. E. histolytica and E. dispar. On a total of 1,108 patients, 12 cases of amoebiasis and 79 cases of E. dispar infection were diagnosed by real-time PCR. Only 64 cases of E. histolytica/E. dispar infection were detected by microscopy and/or cultivation (5 E. histolytica and 59 E. dispar as determined by real-time PCR) traducing in a missed diagnosis of 7 cases of amoebiasis (6 of whom extra-intestinal). Conclusion: All the real-time PCR assays proved to be in our hand a useful tool for the diagnosis of infections by protozoa showing a higher sensitivity than conventional assays. Therefore, if available and accessible, they would be the most accurate tool for the diagnosis of intestinal parasitoses.