1.1.1. Case definition
The case definition is the operating definition of a disease for studypurposes. Aristotle identified two crucial components that made for agood case definition: 1. it specifies characteristics common to alldiseased individuals; and 2. it specifies how diseased individuals differfrom non-diseased individuals (Koepsell and Weiss, 2003). Ideally, thecharacteristics used to identify the disease should be simple andrecognizable by independent observers in different geographies.Because characteristics cannot always be recognized in the field, caseconfirmation by laboratory analyses is sometimes necessary. Casedefinitions, especially for emerging or newly identified diseases, oftensuffer from having limited specificity. Further, case definitions for adisease can evolve as understanding of a disease changes and / orthe diagnostic tests performed to determine a diagnosis are refined.An outline of different classifications of case definitions has beenprovided by the World Health Organization (WHO, 1999). Whenapplied to apiculture, it is important to define the “epidemiologicalunit” for which the case definition is being applied (discussed ingreater detail in section 1.2). Epidemiological units are the groupswhich make up the population of interest, and can range fromindividual bees, colonies, apiaries, and operations.