Lambs infected with latent cryptosporidiosis excrete Cryptosporidium-oocysts in their faeces. You are evaluating a new test for Cryptosporidium in lambs.

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You have taken 151 faecal samples from lambs on the S.W. peninsular on St. Kitts (an island in the Caribbean) and tested them with a combination of oocysts isolation and PCR (the gold standard approach in this case), which confirms that all lambs are truly infected.

The new test is a coproantigen test for use in ovine faeces. It is positive in 140 of these 151 samples. Likewise in 97 lambs raised in a completely parasite free and Cryptosporidium free environment the coproantigen test is positive on only three faecal samples.