New technologies, human-microbe interactions, and the search for previously unrecognized pathogens.

Evidence suggests that a significant number of clinically important microbial pathogens remain unrecognized. Observations from the natural world, from patterns of disease in human populations, from the bedside, and from the clinical laboratory all contribute to this body of evidence. A variety of acute and chronic neurologic syndromes illustrate this point; despite features of infection, most cases of aseptic meningitis, encephalitis, and cerebral vasculitis cannot be assigned a microbiologic diagnosis. The development and clinical application of molecular methods have led to the discovery of novel members of the endogenous normal flora as well as putative disease agents. Current challenges include the establishment of criteria for disease causation and further characterization of the human microbiome during states of health. These challenges and the goal of understanding microbial contributions to inflammatory disease may be addressed effectively through the thoughtful integration of modern technologies and clinical insight.