v21n07

DEPARTMENT OF PATHOLOGY
The Johns Hopkins Medical Institutions

Vol. 21, No. 7
THE JOHNS HOPKINS MICROBIOLOGY NEWSLETTER
Tuesday, February 26, 2002

Provided by Karen Fujii, Division of Outbreak Investigation, Maryland Department of Health and Mental Hygiene.

* 2 outbreaks of influenza (1 outbreak of lab-confirmed influenza at a nursing home in Frederick Co.; 1 outbreak of Influenza A at a transitional care facility in Montgomery Co.)
* 2 outbreaks of influenza-like illness/pneumonia (1 at a nursing home in Talbot Co.; 1 at a nursing home in Anne Arundel Co. [2 chest X-ray confirmed pneumonias])
* 1 outbreak of influenza-like illness at a nursing home in Frederick Co.
* 5 gastroenteritis outbreaks (1 at a nursing home in Cecil Co.; 1 at a nursing home in Prince George's Co.; 1 at a nursing home in Montgomery Co.; 2 in Washington Co.[1 at an assisted living facility, 1 at a nursing home])
* 1 shigellosis outbreak at a school in Anne Arundel Co.
* 4 foodborne gastroenteritis outbreaks (2 associated with a store in Prince George's Co.; 1 associated with a restaurant in Howard Co.; 1 associated with a fast food restaurant in St. Mary's Co.)
1 outbreak of scabies at a nursing home in Baltimore Co. B. The Johns Hopkins Hospital, Department of Pathology, Information provided by M. Ali Ansari-Lari, MD, Ph. D. Case presentation: An institutionalized 18 year-old male with severe mental retardation presented with a 3 week history of vomiting and a 2 week history of non-bloody diarrhea, averaging 4-5 stools per day. He was afebrile. His abdomen was soft with mild pain on palpation. The remainder of his physical exam was unremarkable. His white blood cell count was 5,270 with normal differential. His stool culture was negative for enteric pathogens. However, the analysis of his stool for ova and parasites revealed many Dientamoeba fragilis. He was started on iodoquinol therapy. Dientamoeba fragilis

Organism and Laboratory Diagnosis:

D. fragilis is a protozoan parasite which was originally classified as an amoeboid organism. Despite the lack of flagella, based on morphologic, electron microscopic, and 16S-like rRNA sequence findings, it has been reclassified as a flagellate. It is closely related to Trichomonas. D. fragilis measures 5-15 ?m is size on wet preparations and 1 to 2 ?m less on permanent stains. It has a nonprogressive motility by pseudopodia. The trophozoite has 1 to 2 nuclei. There is no cyst stage as part of its life cycle. The organism predominantly resides in the cecum and the proximal part of the colon.

The recovery of D. fragilis is greatly improved by obtaining at least 3 stool samples. On a wet mount, the organism does not show distinct nuclear structures, making the diagnosis very difficult. The detection rate is greatly enhanced after staining of fixed fecal smears. The most commonly used stains are Gomori and iron hematoxylin. The most sensitive method of D. fragilis detection is by culture; however, most laboratories do not offer it.

Epidemiology: The prevalence rates of D. fragilis reported in stools after routine parasitologic examination ranges from 1.5% (Australia) to 41.5% (Germany). In one study, the prevalence among the general population of Oakland, California, screened during routine health examination, was approximately 3%. In a screen of healthy children in day care centers in Toronto, the prevalence of D. fragilis was approximately 8%. The organism can be detected both in soft and solid stools. The variability in detection rate may be as a result of sampling and detection methods. Due to the lack of cyst stage, the mode of transmission of D. fragilis is not well understood. It is unlikely that the organism survives in the environment or in water for any length of time. The much higher incidence of D. fragilis in certain close-living populations with poor personal hygiene, suggests direct fecal-oral transmission. Several studies indicate association between D. fragilis and Enterobius vermicularis (pinworm) infections. Although not proven, ova of E. vermicularis might be the vector for transmission of D. fragilis. Using riboprinting, two genetically distinct variants of D. fragilis have been identified.

These two variants may represent pathogenic and nonpathogenic strains of D. fragilis, accounting for existence of asymptomatic infections (3).

Clinical presentation: In Children, up to 90% of infections are symptomatic whereas in adults this frequency is much lower (15-25%). The most common symptoms are abdominal pain and diarrhea, which may contain blood and mucus. The abdominal pain can persist up to two months and is more frequently seen in chronic infection, while diarrhea usually lasts 1-2 weeks. Other symptoms may include nausea and vomiting, flatulence, anorexia, weakness, fever and weight loss. Biliary infection and suppurative appendicitis are rare reported complications. Approximately 30% of children with D. fragilis infection exhibit peripheral blood eosinophilia. Treatment: The treatment of choice in symptomatic individuals is tetracycline. However, tetracycline is not recommended in children due its side effects. Iodoquinol is considered the treatment of choice by some authors. Other effective medications include metronidazole, and if there is concomitant E. vermicularis infection, mebendazole. References:

Windsor, JJ, Johnson, EH. Dientamoeba fragilis: the unflagellated human flagellate. Br J Biomed Sci. 1999; 56:293-306.
Dickinson, EC, et al. Dientamoeba fragilis: a significant pathogen. Am J Emerg Med. 2002; 20:1-
Johnson, J. Clark, G. Cryptic genetic diversity in Dientamoeba fragilis. J Clin Microbiol. 2000; 38:4653-4654.

Murry, PR, Baron, EJ, Pfaller, MA, Tenover, FC, Yolken, RH. Manual of clinical microbiology (7^th edition). 1999. ASM Press, Washington, DC.