Diagnostic approaches for patients with suspected encephalitis.

Encephalitis represents a diagnostic challenge, with an infectious etiology identified in only 40% to 70% of cases. More than 100 agents have been either definitively or anecdotally associated with encephalitis. Important considerations for diagnosis include selection of the appropriate clinical specimen (serum vs cerebrospinal fluid), determining the most sensitive diagnostic assay (serology vs polymerase chain reaction), and assessing causality when an organism is identified outside of the central nervous system (eg, a positive nasal swab for influenza). This review aims to provide an evidence-based, clinically relevant approach to the diagnostic evaluation of patients presenting with encephalitis, focusing on the most common or important causes in the immunocompetent host. Diagnostic issues associated with encephalitis due to herpes-group viruses, arboviruses (including West Nile virus), rickettsiae, bartonella, enteroviruses, and rabies are discussed in-depth. Diagnostic testing should be individualized based on clinical presentation and epidemiology.