Prevention of disease is divided into 3 levels. Primary prevention is aimed at maintaining a healthy population; i.e., preventing the occurrence of disease. Secondary prevention (also called disease control) attempts to minimize resultant damage after disease has occurred and primary prevention has failed. Tertiary prevention consists of rehabilitation after primary and secondary prevention have failed.
Primary prevention involves the healthy population. Secondary and tertiary Prevention is aimed at the diseased or patient population. The economic aspect of disease prevention is of paramount importance; particularly in considering food animals. Simply stated, as one progresses from primary through secondary to tertiary prevention, the cost per animal unit usually increases.