The evaluation of patients with opportunistic lung infection is often a confusing and frustrating ordeal for the physician. A diagnostic and therapeutic dilemma often ensues. The diagnostic dilemma stems from the nonspecificity, costs, and risks of tests designed to delineate the etiology of the infection. The therapeutic dilemma arises because many opportunistic infections have no satisfactory treatment. Additionally, patients often have such a rapidly fatal underlying disease that resorting to invasive procedures to diagnose either a potentially untreatable infection or a pathological manifestation of an underlying disease, although academically interesting, seems to be cruel and unusual punishment.
Part of the decision analysis includes the likelihood of rapid deterioration if empiric treatment fails. Thus, no algorithm can be developed that satisfactorily provides a generic approach to this difficult problem. General principles that guide the decision analysis include a rapid history and physical examination, chest roentgenogram, and the collection of respiratory secretions
Bone RC. Opportunistic Pneumonia: A Stepped Approach. JAMA. 1985;253(12):1783. doi:10.1001/jama.1985.03350360109032