A diagnostic approach to Pneumocystis jiroveci pneumonia

Pneumocystis jiroveci, the etiologic agent of pneumocystis infection in humans, was first described in 1909 by Carlos Chagas, who, in his study of guinea pigs, mistookthecystsforthesexualstateofTrypanosomacruzi (1). Severalyearslater, the Delanoes, a husband-and-wife team of scientists, realized that the cysts were a separate entity when they found them in the lungs of Parisian sewer rats that did not have trypanosomiasis (2). They named the organism Pneumocystis carinii in honor of Antonio Carini, a contemporary of Chagas, even though he, too, had thought it was a trypanosome (3). Since then, pneumocystis organisms have been identified in a wide range of other host species, including humans. Not until the 1960s, however, was pneumocystis deemed a significant opportunistic pathogen in humans. With the aid of bronchoscopy in the 1970s, the organism wasidentifiedwithincreasingfrequencyinpatients withmalignantneoplasmsand in patients with congenital or drug-induced immunosuppression. Then, in the 1980s, pneumocystis pneumonia (PCP) became widely recognized as one of the most common presenting manifestations of the Acquired Immunodeficiency Syndrome (AIDS) in North America and Europe. With the development of more sophisticated laboratory techniques, the diagnosis of PCP can be definitively established by rapid, noninvasive