The words infectious and contagious are often used interchangeably, but they do not mean exactly the same things. We’ll look at the difference between the words infectious and contagious, the origins of the terms and a few examples of their use in sentences.
Infectious refers to diseases that are contracted through the environment. In fact, someone who is ill with an infectious, non-contagious disease can not spread the disease by physical contact. Infectious diseases are caused by bacteria or viruses. Examples of infectious diseases are Lyme disease and malaria. Infectious is also used in a figurative sense to mean something that spreads easily and rapidly. The word infectious is derived from the Old French word infeccion, which means poison or contagion.
Contagious refers to a disease that is spread by direct physical contact between people or animals. This use of the term direct physical contact includes items that the ill individual may have touched. All diseases are infectious, but only some diseases are contagious. Some examples of contagious diseases are smallpox and influenza. Contagious is also used figuratively to describe something that spreads easily and rapidly. The word contagious is derived from the Old French word contagieus. Remember, all diseases are caused by a pathogen and are therefore infectious, but only diseases that are communicated through direct physical contact are contagious.
The city of Flint, Mich., is facing an outbreak of an infectious disease called shigellosis, according to local reports. (USA Today)
Anil also entertained the audience with his infectious laughter and energy. (The Indian Express)
More than a dozen Clark County high school football players infected with the contagious skin disease impetigo has prompted public health and school leaders to take action. (The Springfield News-Sun)
Yawning seems to be pretty much ubiquitous in the animal kingdom, and for some animals — many humans included — it really is contagious. (The Washington Post)