True versus apparent prevalence.

As can be inferred from the discussion above, the reported point prevalence of disease is influenced by the case definition and the test employed to determine a case’s outcome. It is conceivable that for some diseases, in-field examination for phenotypic expression of disease may be negative while laboratory tests determine disease presence (i.e. deformed wing virus). In such cases, two types of prevalence can be specified; true prevalence with all cases of disease existing at a specific point in time, and apparent prevalence that is determined by test results (i.e. in-field examination, molecular test, etc.). The apparent prevalence is subject to the accuracy of the test (sensitivity and specificity).