How Contagious Are Common Respiratory Tract Infections?

Abstract

This article will follow consistent usage. Infections are diseases caused by infectious agents — microorganisms that can be cultivated and transmitted. Transmissibility or communicability refers to the capacity of an infectious agent to spread from one person to another. Once transmitted, organisms may colonize (proliferate on the skin or in a cavity or a viscus) or infect (invade and proliferate in tissues) or do both; colonization is often a necessary step in the sequence of events leading to bacterial, but not to mycobacterial or viral, infection. Infection, which may be asymptomatic (subclinical) or may cause symptoms (disease), nearly always occurs in association with an immune response. Contagion results when an organism is transmitted from one person to another, causing disease. Virulence describes the capacity of an organism to infect, but the term tends to be used more loosely to denote the tendency to cause serious disease.