Infectious diseases are diagnosed when a bacterium, virus, fungus, protozoan, or helminth is found in a patient with a compatible clinical illness. Methods of detection include cultivating bacteria and fungi on growth medium, isolating viruses in cell culture, and identifying the agent biochemically, antigenically, or genetically. Infectious diseases can also be identified by detecting a specific immune response, usually antibodies, that develops during the course of illness. Infectious Disease Diagnostics of an agent in infected tissue can provide a diagnosis based on specific morphological characteristics or identify the category of organism, such as gram-positive or gram-negative bacterium or virus (e.g., eosinophilic cytoplasmic inclusion bodies in neurons in rabies virus infection).
