increased disease or injury severity (e.g., its morbidity or mortality or other determinants of severity); occurrence of a rare or unknown disease or a change in the pattern of the disease's occurrence; opportunity to identify new information (e.g., risk factors previously unassociated with that disease or a change in transmission method); occurrence among a particular population (e.g., children or older persons); public or political concern; opportunity to conduct research on a specific disease; and opportunity to train personnel (e.g., EISOs or state and local field investigators) in the methodology of field investigations