Ans. B: Immunofluorescence test Diagnosis of cryptosporidium is made by demonstration of oocyst in feces Methods of detection and confirmation of cryptosporodium Wet mount-In bright-field microscopy using differential interference contrast (DIC), oocysts appear as small round structures (4 to 6 im) similar to yeasts. They do not autofluoresce. Modified acid-fast stain-Oocysts (4 to 6 im) often have distinct oocyst walls and stain from light pink to bright red. In paicular, infections that are resolving can have colorless oocyst "ghosts." Mature oocysts may have discernible sporozoites (up to 4). Indirect fluorescent antibody assay-This technique offers the highest combination of sensitivity and specificity and is considered the gold standard. However, it does not provide a stained slide that can be archived. It requires special equipment (fluorescence microscope) and commercially available test kits. Methods for detection (but not confirmation) of Cryptosporidium Oocysts may be detected by the following methods, but should be confirmed by the diagnostic techniques listed above. Safranin stain-Oocysts of Cryptosporidium often (but not always) stain a bright reddish-orange color. This method, advocated for Cyclospora, is not widely used for Cryptosporidium because the Cryptosporidium oocysts may not always properly stain. - Trichrome stain-Oocysts may be detected, but should not be confirmed, by this method. This staining method is inadequate for definitive diagnosis because all oocysts will appear unstained. Oocysts appear as small round structures measuring 4 to 6 im. Other methods for detecting Cryptosporidium in stool. - Enzyme immunoassay (EIA)-The EIA does not rely on microscopy skills, is highly sensitive and specific, and is useful for screening large numbers of specimens. - Rapid immunochromatographic caridge assays-The rapid caridge assays may be used with preserved specimens and are quick and easy to perform