Diagnostic clues often are not readily apparent on physical examination; repeated examination may be essential. Careful attention to the skin, mucous membranes, and lymphatic system, as well as abdominal palpation for masses or organomegaly, is important. The physician's choice of imaging should be guided by findings from a thorough history and physical examination 21 (., a cardiac murmur in the presence of negative blood cultures should be investigated with a transthoracic echocardiogram or, if needed, transesophageal echocardiogram) rather than strictly following the stepwise approach outlined in Figure 1 . Also, Duke's clinical criteria include two major and six minor criteria that help determine the likelihood of endocarditis. 22 [Evidence level A, validated clinical decision tool] A cost-effective individualized approach is essential to the evaluation of these patients, and without a thoughtful and focused investigation, inappropriate tests might be performed.
Historical and even recent reports of P. carinii from humans are based upon older classifications (still used by many, or those still debating the recognition of distinct species in the genus Pneumocystis ) which does not mean that the true P. carinii from rats actually infects humans. In an intermediate classification system, the various taxa in different mammals have been called formae speciales or forms. For example, the human "form" was called Pneumocystis carinii f. [or f. sp.] hominis , while the original rat infecting form was called Pneumocystis carinii f. [or f. sp.] carinii . This terminology is still used by some researchers. The species of Pneumocystis originally seen by Chagas have not yet been named as distinct species.  Many other undescribed species presumably exist and those that have been detected in many mammals are only known from molecular sample detection from lung tissue or fluids, rather than by direct physical observation.   Currently, they are cryptic taxa.