Dictionary > Focus


noun, plural: foci
(general) A central point
(pathology) The central site in which a disease localizes or develops
In biological and pathological contexts, focus refers to the site in the body wherein a disease first develops, or that which localizes. A theory relating to it is called focal infection theory. In this theory, a localized site of infection disseminates microbes or toxins away from the central source. The spread of infection to distant sites may lead to secondary infections. Examples of sites that serve as focus of infection are oral tissues, appendix, bladder, gall bladder, kidney, liver, prostate, and sinuses. The most common focal site of infection is the oral tissues. Proponents of this theory believe that certain diseases could have established over time and could have come from the focal site of infection. However, this theory was largely criticized by many scientists and researchers, and Hobart A Reimann and W Paul Havens were its strong critics.1
Word origin:
Related term(s):

  • focal
  • Friend spleen focus forming virus
  • Plasma focus
  • Natural focus of infection
  • Condenser variable-focus
  • Focus principal
  • Mink cell focus-inducing viruses
  • Ghons focus
  • Principal focus
  • Real focus
  • Virtual focus


1Reimann, Hobart A.; Havens, W. Paul (1940). “Focal Infection and Systemic Disease: A Critical Appraisal”. Journal of the American Medical Association 114. doi:10.1001/jama.1940.02810010003001.

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