A necessary part of the investigation of any disease in the population at risk for that disease is the counting of affected animals. This procedure is necessary in order to describe the amount of disease (morbidity) in terms of its spatial distribution (places of occurrence) and temporal distribution (times of occurrence of cases of the disease). Consequently, this section of the outbreak surveillance plan focuses on the population at risk from which the target population and study population will be chosen.
The Target Population and Study Population that will be surveilled should be described. The target population is the total population about which information is required. Ideally this should be the population at risk. The study population is the population from which a sample is drawn. Typically, the target population and study population should be the same. However, for reasons of practicality, this may not be possible. If the study population is not representative of the target population, then inferences about disease in the target population should not be generalized beyond the study population.
Define the target population and study population to surveil.
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As a starting point, information from the State Animal Health Official, Federal Assistant Director (AD), Federal Area Emergency Coordinator (AEC) for the State, and/or individuals involved in the emergency response with local knowledge should be used to identify specific information about the target population and study population of premises and the animal species contained therein that are susceptible to the disease in question.
Alternatively, the National Agricultural Statistics Service (NASS) resources may also be used to help define the target population and study population. However, because NASS data is collected at the county level, it is likely useful only if control zones are defined on a county basis.
Tip: NASS resources can be helpful in defining a target population and study population, but it may also take a great deal of time to sort through NASS data to find the desired information. It may be necessary to develop a rough draft of the target population and study population description initially and then refine it later as more information is gained, either from NASS or local experts.