Diagnosis of infectious disease is nearly always initiated by medical history and physical examination. More detailed identification techniques involve the culture of infectious agents isolated from a patient. Culture allows identification of infectious organisms by examining their microscopic features, by detecting the presence of substances produced by pathogens, and by directly identifying an organism by its genotype. Other techniques (such as X-rays, CAT scans, PET scans or NMR) are used to produce images of internal abnormalities resulting from the growth of an infectious agent. The images are useful in detection of, for example, a bone abscess or a spongiform encephalopathy produced by a prion.
How is diagnosis of infectious disease almost always initiated? What does taking a culture of an infectious agent isolated from a patient allow? What features of an infectious organism does a culture allow examining? What can organisms be directly identified by? What technique can be used to produce images of internal abnormalities?