Adult patients who present with recurrent infections pose a dilemma to the generalist. In most cases, there is a secondary cause, such as an anatomic abnormality. However, secondary immune defects due to other medical disorders are sometimes identified, while primary immune defects presenting in adults are rare. The initial approach to an adult patient with recurrent infections is discussed here, with a discussion of the nonimmunologic disorders that should be considered in the evaluation of recurrent infection at specific anatomic sites, and a brief overview of immunodeficiency in adults. The laboratory tests that are used to evaluate the various components of the immune system are reviewed separately. (See "Laboratory evaluation of the immune system".)
OVERVIEW OF ETIOLOGIES
In adults, recurrent infections are usually due to an anatomic lesion or to a secondary cause of immune suppression.
It is helpful to consider the following broad categories of etiologies when evaluating an adult with recurrent infections:
●Anatomic lesions, whether congenital or acquired, and disorders affecting the function of specific organs are important causes of recurrent infections in adults (table 1).
●Secondary immune disorders due to other medical conditions or treatments for these conditions are a much more common cause of recurrent infections than primary immunodeficiencies (table 2). (See 'Secondary immunodeficiency' below.)