RESUMEN
BACKGROUND: Giardia duodenalis is a common cause of chronic diarrhea especially in tropical countries. Diagnosis is based on microscopy (three stool samples) for trophozoites/cysts. Role of stool or duodenal biopsy PCR as a diagnostic method needs to be defined. We conducted a prospective study to determine the diagnostic characteristics of G. duodenalis stool and duodenal biopsy PCR in comparison to stool microscopy (reference standard). Later, we compared other techniques with stool PCR, considering it as new reference standard and characterized the type of Giardia assemblage. METHODS: G. duodenalis stool nested PCR was first evaluated using 40 positive controls and 50 negative controls considering stool microscopy as reference standard. Patients with chronic diarrhea (n = 100) were evaluated by stool microscopy and nested PCR. In 30 patients in whom upper gastrointestinal endoscopy was performed, duodenal biopsy samples were obtained and evaluated by histopathology, imprint cytology, and nested PCR. The type of Giardia assemblage was detected by assemblage-specific PCR. RESULTS: Stool nested PCR was found to have sensitivity and specificity of 100% and 94%, respectively, compared to stool microscopy. In patients with chronic diarrhea, 48% had evidence of Giardia infection. Stool microscopy detected 65%, stool PCR detected an additional 27%, and duodenal biopsy PCR detected an additional 8% of cases. The commonest assemblage found was assemblage B. Clinical and demographic characteristics were similar in patients harboring either assemblage A or B. CONCLUSION: Stool PCR is more sensitive than stool microscopy. By utilizing stool microscopy, stool nested PCR, and duodenal biopsy PCR in sequential manner, diagnostic yield can be increased.