Decision Analysis for Isoniazid Chemoprophylaxis

To the Editor. —  Colice is to be commended for his meticulous effort, through the use of decision analysis,¹ to resolve the controversy regarding isoniazid chemoprophylaxis for young purified protein derivative (PPD) reactors of unknown date of conversion, with a normal chest roentgenogram, and with no additional risk factors for developing tuberculosis. As he notes, three previous decisionanalysis studies have reached conflicting conclusions. With the addition of the current study, the "score" now stands as two^1,2 favoring the American Thoracic Society/Centers for Disease Control recommendation, and two^3,4 failing to support it.In all of these studies,^1-4 the decision trees are similar in design in that the "no isoniazid" limb is followed by a "tuberculosis—no tuberculosis" chance node. What is missing in terms of clinical relevance is a "risk factorno risk factor" branch point prior to the possible development of tuberculosis. Those physicians who advocate not giving