The diagnosis of giardiasis by a real-time polymerase chain reaction assay as compared to conventional assays.

Objectives: Giardia intestinalis is a world-wide distributed parasitic agent of gastroenteritis with a higher frequency in warm climate. As giardiasis is one of the most frequent parasitoses in our area, the aim of this study was the evaluation of the performance and of the applicability of a real-time PCR assay in comparison with the combination of conventional methods used in our laboratory for the diagnosis of the infection by G. intestinalis. Methods: The DNA from 800 faecal samples collected in a 3-year period and belonging to 403 patients with a clinical suspicion of intestinal parasitosis was used in a real-time PCR assay for the detection of G. intestinalis [1]. The same samples were analyzed for the presence of intestinal parasites by conventional methods (microscopic examination from fresh and concentrated faecal material and G. intestinalis and Cryptosporidium spp. specific antigen detection by immunocromatographic and/or immunofluorescence assays). Results: G. intestinalis was detected in 178 samples of 98 patients by conventional methods, while the real-time PCR assay revealed the DNA of the protozoan in 26 additional samples. In particular in 13 cases the diagnosis was possible only by using the molecular assay evaluated in this study. The detection limit of the real-time PCR assay was 2 cysts per reaction. As concerns the diagnostic performance, the real-time PCR assay showed a sensitivity and a specificity both of 100% as compared to conventional assays for the diagnosis of the infection by G. intestinalis. Discussion: In our experience, the evaluated real-time PCR assay demonstrated to be a specific and sensitive tool for the detection of G. intestinal infection. This assay could be successfully associated to the conventional methods for the diagnosis of intestinal parasitoses in our laboratory, in order to perform an accurate diagnosis of giardiasis, especially in groups of selected patients such as subjects presenting with risk factors for faecal-oral infections including immigrants and adopted children from developing countries and travellers returning from the same areas [2]. Reference(s) [1] Verweij JJ. et al. J Clin Microbiol 2004; 42:1220–1223. [2] Calderaro A. et al. Diagn Microbiol Infect Dis 2009; In press.