Pediatric Cryptosporidiosis Workup

Imaging studies are not indicated as a first-line diagnostic approach in cryptosporidiosis.

Abdominal radiography and computed tomography (CT) scanning are nonspecific and may reveal distended loops of bowel, air-fluid levels, and disrupted bowel motility.

When indicated, as guided by symptoms, ultrasonography or CT scanning may reveal an enlarged gallbladder with a thickened wall, dilated or irregular intrahepatic and extrahepatic biliary ducts, and a normal or stenotic distal common bile duct.

In cases of respiratory involvement, chest radiography is unremarkable, with modest infiltrates or increased bronchial markings.

Cholangiography may reveal beading of the common bile duct or papillary stenosis.

Cryptosporidium can be difficult. Most often, stool specimens are examined microscopically using different techniques (eg, acid-fast staining, direct fluorescent antibody [DFA], and/or enzyme immunoassays for detection of Cryptosporidium species antigens). Go to Cryptosporidiosis for complete information on this topic.

Collection

Follow collection recommendations and precautions on routine parasitologic examination of stools. For immunodiagnostic assay kits, follow the manufacturer’s instructions.

Transport

If immediate examination is not possible, use one of several preservatives, such as 5-10% buffered formalin, merthiolate-iodine-formalin (MIF), or SAF. Refrigerate unpreserved specimens to delay deterioration. Do not freeze specimens.

Processing

Unconcentrated, fresh specimens can be examined by wet mount preparations. Concentration by the formalin ethyl acetate method is preferable. Optimal centrifugation time and speed, 10 minutes at 500 X, are critical for concentrating Cryptosporidium oocysts. Commercial fecal concentration tubes are available that decrease processing time and supplies needed for concentrating specimens (eg, Fecal Parasite Concentrator, Evergreen Scientific). PVA-preserved specimens are not acceptable for modified acid-fast staining for detection of Cryptosporidium.

Examination techniques

Modified acid-fast staining procedure is useful for the identification of oocysts of the coccidian species (Cryptosporidium, Cystoisospora, and Cyclospora), which may be difficult to detect with routine stains, such as trichrome. Cryptosporidium species stain a pinkish-red color. The background should stain uniformly green. Unlike the Ziehl-Neelsen modified acid-fast stain, this stain does not require the heating of reagents for staining. (See the images below.)

A monoclonal antibody-based fluorescein conjugated stain for oocysts in stool is commercially available. An enzyme immunoassay (EIA) to detect antigen in stool is also commercially available and is the most specific, reliable test that is widely available.^[15]

Specimen examination

Concentrated sediment of fresh (within 30 min after passage of stools) or formalin-preserved stool may be used. Other types of clinical specimens, such as duodenal fluid, bile, and pulmonary samples (induced sputum, bronchial wash, biopsies) may also be stained. The sucrose flotation method or formalin ethyl acetate method is used to concentrate stool before staining with a modified Kinyoun acid-fast stain, because routine laboratory examination of stool for ova and parasites does not detect Cryptosporidium.^{[2, 4]} This technique stains oocysts pink or red, whereas fecal debris or yeast assumes the color of blue or green counterstain.

Because shedding may be intermittent, examine at least 3 stool specimens collected on separate days before considering the test results negative. Fecal leukocytes are not found in stool specimens because it does not invade below the epithelial layer of the mucosa.

Oocysts are small (4-6 μm in diameter) and can be missed without a very careful examination of the slide.

GI biopsy specimens can be used instead of stool specimens. A high concentration of oocysts is seen in the jejunum.

Electron microscopy of stool or biopsy specimens can also be performed for direct visualization of oocysts.

For research purposes and for species identification, polymerase chain reaction (PCR) assays are used.

Serologic detection of specific anti-Cryptosporidium antibodies is primarily used as a research or epidemiologic tool.

GI or liver biopsy may be indicated in cases of diagnostic uncertainty. Different parts of the intestinal tract may be affected. Liver biopsy findings may reveal the organism attached to bile duct epithelial cells. Concurrent infection with cytomegalovirus (CMV), Enterobacter cloacae, and microsporidia is common.

In patients with related symptoms, bronchoalveolar lavage or lung biopsy findings may reveal the parasite in lavage fluid, in brush biopsy specimens, attached to the surface of bronchial mucosal cells, or in macrophages. In most instances, another pulmonary pathogen, such as CMV or Pneumocystis carinii, is concurrently detected; however, in a series of 4 patients infected with HIV, Cryptosporidium was the only pathogen identified in the respiratory tract. Clear association with intestinal cryptosporidiosis or diarrhea has not been shown in these cases.

Villous atrophy with blunting, epithelial flattening, and an increase in lamina propria lymphocytes are seen in patients with persistent cryptosporidiosis. In patients with heavier infection, crypt hyperplasia and marked infiltration with lymphocytes, plasma cells, and neutrophils are also noted. Biopsy samples of the biliary ducts may reveal the parasites.