Laboratory diagnosis of Blastocystis spp. in diarrheic patients.

Background: Many laboratories currently diagnose Blastocystis spp. infections by looking for the presence of vacuolar forms in faeces and the amoeboid form in diarrheal stools.

Objective: To investigate the best direct method in diagnosis of Blastocystis spp. and to study different morphological forms of the parasite.

Methods: The study was carried out on one thousand and two hundred diarrheic stool samples. All samples were examined using direct smear, iodine stained smear, formalin-ether concentration techniques, trichrome stained smear and in vitro cultivation using Jones' medium.

Results: Using direct smear, Blastocystis spp was detected in 42 cases (3.5%) with a sensitivity (28.4%) and specificity (100%). Iodine stained smear detected 72 positive cases (6%) with a sensitivity (48.7%), specificity (100%). Formol ether concentration technique detected 120 positive cases (10%) with a sensitivity (81.1%) and specificity (100%). Trichrome stained smear detected 148 positive cases (12.3%). In vitro cultivation using Joni's medium detected 274 positive cases (22.8%) which was the highest number among all different diagnostic methods with a sensitivity (100%) ,specificity (88%), PPV (54.1%) and NPV (100%). It was found that, 49 blastocystosis cases had mixed infection with other intestinal parasites. Giardia lamblia was the most frequently associated parasite with Blastocystis spp.

Conclusions: In vitro cultivation is more sensitive in detection of B. hominis than simple smear and concentration technique. Blastocystis spp. vacuolar form was the most common form that was found by all methods used in this study G. lamblia was the most frequent parasite associated with Blastocystis spp .