Amebic colitis in an antigenically and serologically negative patient: usefulness of a small-subunit ribosomal RNA gene-based polymerase chain reaction in diagnosis

Specific identification of Entamoeba histolytica in clinical specimens is an essential confirmatory diagnostic step in the management of amebiasis. Here, we report an unusual case of amebic colitis in a 20-year-old female immigrant from South China. The patient had experienced diarrhea, crampy abdominal pain, and fever for approximately 3 weeks prior to admission to hospital and had treated herself at home with metronidazole. On admission, stool microscopy and serology for E. histolytica were negative. Because the clinical findings raised the suspicion of Clostridium difficile fulminant colitis, she underwent a subtotal colectomy. Histopathology revealed flask-shaped ulcers characteristic of amebic colitis. Consequently, E. histolytica DNA was detected by a sensitive small-subunit rRNA polymerase chain reaction (PCR) from feces, and the patient was successfully treated for amebiasis with metronidazole. This case exemplifies the relative insensitivity of serologic tests for the diagnosis of intestinal amebiasis and the difficulties encountered in detecting the parasite antigen in a patient partially treated with metronidazole. We conclude that when the possibility of invasive intestinal amebiasis is suspected, detecting the parasite DNA directly in the stool sample by PCR using E. histolytica-specific primers may be an alternative, noninvasive, and reliable tool for the specific diagnosis of the disease.