Vol

DEPARTMENT OF PATHOLOGY The Johns Hopkins Medical Institutions

Vol. 18, No. 4
THE JOHNS HOPKINS MICROBIOLOGY NEWSLETTER
Monday, January 25, 1999

Provided by Leslie Edwards Reger, Division of Outbreak Investigation, Maryland Department of Health and Mental Hygiene.

13 outbreaks reported: 3 foodborne gastroenteritis: 2 in food-service facilties, 1 resulting from a dinner prepared in a private home, 7 influenza-like illness outbreaks in nursing homes, 1 ringworm outbreak in a school, 1 respiratory syncytial virus outbreak at a medical facility, and 1 acute respiratory disease outbreak at a nursing home

The Johns Hopkins Hospital. Information provided by Dr. Michael Dardik, Department of Pathology.

Clinical Information: A 41-year-old female experienced abdominal discomfort and diarrhea for approximately three weeks. Laboratory studies included WBC 6100/ cu mm (neutrophils 76%, eosinophils 2%, lymphocytes 16%), hemoglobin 14.0 g/dL, and platelets 242 K/cu mm. Urinalysis and a comprehensive metabolic panel were unremarkable. Flexible sigmoidoscopy was unremarkable. Stool bacteriology culture was negative for enteric pathogens. A Clostridium difficile toxin assay was negative. A stool specimen was sent for ova and parasites and Dientamoeba fragilis was identified. In the interim, the patient’s symptoms spontaneously resolved and no therapy was instituted. Dientamoeba fragilis Dientamoeba fragilis is a protozoan parasite with no recognized cyst stage. Although previously classified as an amoeba, ultrastructural and immunologic studies have demonstrated that the organism is a flagellate, despite its having no observable flagella. The trophozoite typically has two nuclei with four to eight large granules. As the trophozoite does not survive outside the bowel for more than 24 hours and ruptures in fresh water, a food or waterborne transmission is unlikely. Direct fecal-oral transmission may occur; however, the higher than expected association of Dientamoeba fragilis with Enterobius vermicularis suggests that Enterobius vermicularis eggs may be infected with the flagellate and serve as the vector of transmission.

Clinical Features: Dientamoeba fragilis colonizes the cecum and ascending colon with a quoted incidence in the general population of 2-4%. In certain specific populations, including Native Americans of South Dakota and Arizona, inmates, and communities with poor hygiene, the incidence is higher, between 20% and 70. Colonization does not mean infection, but 90% of colonized children and 25% of colonized adults experience disease. The disease is most commonly characterized by non-bloody diarrhea and abdominal pain, with occasional reports of nausea, vomiting, fatigue and weight loss.

Diarrhea predominates early in the course of the disease and the abdominal pain manifests later.

Diagnosis: The standard of diagnosis is stool examination. Due to the fragility of the organism’s cytoplasm, wet mounts are inappropriate. Fresh stool samples should be immediately preserved in polyvinyl alcohol, sodium acetate-acetic acid-formalin, or Schaudinn’s fixative, and then permanently stained with either trichrome, hematoxylin, or celestin blue B. Even under ideal circumstances, a single stool specimen is diagnostic only 50% to 60% of the time; three samples increases the sensitivity to 80% and six samples to 95%. Due to the suspected pathogenesis of the disease, once Dientamoeba fragilis is diagnosed, Enterobius vermicularis should be sought.

Treatment: Symptomatic adults should be treated with iodohydroxyquin and symptomatic children with metronidazole. Clearance of the organism should be demonstrated by a negative ova and parasite examination of stool ten days after treatment is completed.

References:

Butler WP. Dientamoeba fragilis: An unusual intestinal pathogen. Digestive Diseases and Sciences 41 (9): 1811-1813. Sep. 1996.
Grendon JH, DiGiacomo RF, Frost FJ. Descriptive features of Dientamoeba fragilis infections. Journal of Tropical Medicine and Hygiene 98: 309-15. 1995.

Laboratory Update: Effective immediately, stool specimens for ova and parasite examination taken from hospital inpatients after three days in the hospital will not be accepted. This policy is in accordance with the policies of other major teaching institutions. Questions on this policy or need for exemption can be addressed with the Microbiology Faculty/Residents.