[Microscopy vs. molecular biology in the diagnosis of intestinal protozoal infections, is it time for a change?]

Objective: Microscopic examination of the intestinal parasites, from the patient's concentrated feces, has a lower sensitivity when compared to molecular diagnostic techniques. Therefore, the objective of this study has been to compare both techniques, as well as to evaluate whether there is a correlation between the microscopic examination and the threshold cycles (Ct) obtained for Blastocystis hominis.

Methods: Retrospective study of the samples received in the Microbiology laboratory during September 2021. The MiniParasep SF® concentration test was performed for microscopic visualization and then PCR was performed with the Seegene AllplexTM Parasite Assay panel.

Results: A 27% (n=74) of the samples were positive by molecular diagnosis, with a total of 87 parasites detected. 53% (n=39) were women with a mean age of 47 ± 24 years. In 76% (n=56) of the cases the service of origin was Primary Care. The most frequently found parasite was B. hominis, 85% (n=64), followed by Dientamoeba fragilis 20% (n=15) and Giardia lamblia 11% (n=8). Co-infection by two parasites was detected in 13 cases (B. hominis + D. fragilis in 6 cases, and B. hominis + G. lamblia in 7 cases). In the microscopic diagnosis, 9.5% (n=26) positivity was obtained. The most frequently found parasite was B. hominis, 84% (n=23), followed by G. lamblia, which was seen in three cases by microscopy. D. fragilis was not seen in any case. Coinfection of B. hominis + G. lamblia was observed in one sample.

Conclusions: Techniques for molecular diagnosis of intestinal parasites are fast, reliable and more sensitive than microscopic techniques, improving microbiological diagnosis and quality of care.