ABSTRACT
Blastocystis hominis is now gaining acceptance as an agent of human intestinal disease. This case-control study of the prevalence of B. hominis infection in children less than 6 years old was conducted in an urban area and a rural area in Alexandria. A total of 600 stool samples were examined by wet mount preparation, Merthiolate iodine Formaldehyde concentration technique and permanent staining by using modified Ziehl Neelsen and trichrome stains. The difference between the prevalence of B. hominis in infants and preschool children from an urban area [20.33%] was not significantly different from that in a rural area [24%]. The most common clinical manifestations of B. hominis infection were diarrhea, abdominal pain, fever and vomiting. B. hominis was found in 85 [28.33%] of 300 stool specimens of cases with diarrhea and in 48 [16%] of 300 control specimens. Seventy cases [82.35%] of diarrhea had heavy infection [>5 organisms/20 HPF]. The presence of diarrhea with B. hominis infection was more common in boys aged from one to six years, in severely malnourished cases and in areas with no sewage system and in absence of in-house piped water supply. Contaminated water was suspected to be the major source of infection, since several cases were associated with Giardia infection. These findings support the concept of B. hominis pathogenicity in children with diarrhea