There is an increasing demand for diagnostic testing for Giardia intestinalis (G. lamblia) and Cryptosporidium parvum, with a priority being placed on obtaining diagnostic results in an efficient and timely manner. Several commercial companies have developed rapid diagnostic tests that are simple to perform and can be completed in less time than traditional methods for detecting Giardia and Cryptosporidium. We compared one of these rapid tests, the ImmunoCard STAT! (Meridian Bioscience, Inc.) lateral-flow immunoassay, with the MERI-FLUOR direct fluorescent-antibody (DFA) test, the ProSpecT EZ microplate assay for Giardia and the ProSpecT microplate assay for Cryptosporidium, and modified Kinyoun's acid-fast stained smears for the detection of Cryptosporidium using 246 specimens. The MERIFLUOR DFA (Meridian Bioscience, Inc.) test detected the largest number of cases (32 Giardia and 37 Cryptosporidium) infections and was used to calculate the sensitivity and specificity of the other tests. For Giardia, the sensitivities of the ImmunoCard STAT! and the ProSpecT Giardia EZ microplate assay (Alexon-Trend, Inc.) were 81 and 91%, respectively. For detection of Cryptosporidium, the sensitivities of the ImmunoCard STAT!, the ProSpecT Cryptosporidium microplate assay (Alexon-Trend, Inc.), and modified Kinyoun's acid-fast stained smears were 68, 70, and 78%, respectively. Test specificities were equal to or greater than 99%. Specimens with very small numbers of organisms were not detected by the ImmunoCard STAT!, the ProSpecT microplate assay or modified Kinyoun's acid-fast stained smears.Giardia intestinalis (G. lamblia) and Cryptosporidium parvum are recognized as two of the most common intestinal protozoan parasites infecting humans in the United States (7, 9). Outbreaks of giardiasis and cryptosporidiosis, which occur via fecal-oral transmission, are associated with consumption of contaminated food (21, 22) and drinking water (2) and use of day care centers (26) and recreational water venues (2,3,16). Definitive diagnosis requires the microscopic identification of G. intestinalis cysts or trophozoites or C. parvum oocysts in stool samples (11, 19). Giardiasis is often hard to diagnose because of intermittent shedding of organisms (6), requiring examination of stool specimens collected over several days. C. parvum may be challenging to detect on modified Kinyoun's acid-fast stained smears due to its small size (4 to 6 m) (20) and variable staining of the oocysts. Furthermore, microscopic identification requires trained microscopists and involves time and labor for preparing, staining, and examining smears (17,18,23,25,27). As a result, immunoassays for the detection of Giardia and Cryptosporidium stool antigens have replaced microscopy as the routine diagnostic procedure of choice in many hospitals and public health laboratories (12). These immunoassays are reported to be as sensitive and specific as traditional microscopic methods and increase laboratory efficiency by reducing labor, time, and costs (12).The most widel...

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