Translations:Advanced Field Epi:Manual 2 - Diagnostic Tests/182/en
Risk of infection in test-negative animals
The only way to be 100% confident that no animals comprising a particular group are infected with a particular agent is to test every animal in the group with a diagnostic test which has perfect sensitivity and specificity. However, if only a low proportion of individual animals in the group are infected and only a small number are tested there can be quite a high chance that infected groups will be misclassified as uninfected. The following table shows the number of infected animals which may be present but undetected in a population of 100,000, despite a sample testing negative using a test with perfect sensitivity and specificity at the individual animal level.