Laboratory Diagnostic Challenges in Case/ Control Studies of Diarrhea in Developing Countries

Case/control studies of acute infectious diarrhea require accurate and dependable laboratory tests to detect pathogens in samples from both symptomatic patients and healthy control subjects. The methods used to detect these pathogens have usually been evaluated on patient samples only, and their performance on samples from control subjects is mostly unknown. Because many pathogens occur at a high overall frequency in developing countries and thus may be present in a notable proportion of control subjects as well as pa-tients, the relative ability of a diagnostic test to detect these pathogens in diarrheic and normal stools can have a profound effect on the interpretation of case/control data. The laboratory procedures used to detect etiologic agents in patients with acute infectious diarrhea are constantly evolving. Nevertheless, the principles un-derlying the performance and interpretation of these procedures are well established. As with clinical diag-nostic microbiology in general, the choice of the tests used to detect a possible etiologic agent is determined by clinical relevance, practicability, and cost. For th