infectious
adjective
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What is the Difference Between contagious and infectious?
The words contagious and infectious can be confusing because they do not designate wholly distinct categories; something is not either contagious or infectious.
Essentially, infectious diseases and contagious diseases are caused by disease-producing agents such as bacteria and viruses, but they differ in that contagious diseases can be spread to other people by direct or indirect contact.
Anything contagious, such as the flu, is always automatically infectious: if you can catch it from someone, it's being passed to you via an infectious agent, which is the thing that gets you sick—usually a virus or a bacteria.
The reverse, however, isn't true. Just because something is infectious does not mean it's contagious. Food poisoning, for example, is infectious but not contagious: food can be contaminated with a bacteria (an infectious agent) that makes you sick, but you can't give your food poisoning to someone else by shaking their hand or even giving them a kiss.
Both contagious and infectious are also used figuratively, often in much happier contexts: laughter can be contagious; someone's enthusiasm can be infectious. While both words are used figuratively of both pleasant and unpleasant things, contagious is more often chosen for the unpleasant, as when it's grumpiness or fear that seems to be spreading.
Examples of infectious in a Sentence
Mike Stobbe, The Denver Post, 30 Mar. 2024
So much happiness is infectious and can’t but help but rub itself off on visitors.
—Shivani Vora, Forbes, 28 Mar. 2024
Murray: Judy, your elevator enthusiasm is infectious.
—Fortune Editors, Fortune, 27 Mar. 2024
Generally, people are not infectious after five days on the antibiotic.
—Keri Brenner, The Mercury News, 26 Mar. 2024
His positivity is infectious and contributes greatly to the overall morale of the school community.
—The Courier-Journal, 22 Mar. 2024
The enthusiasm Derek brings to his playing is infectious.
—Heide Janssen, Orange County Register, 17 Mar. 2024
Your enthusiasm is infectious, and your curiosity is infectious.
—Diego Ramos Bechara, Variety, 14 Mar. 2024
One child has recovered and is no longer infectious, the health department said.
—Jen Christensen, CNN, 11 Mar. 2024
These examples are programmatically compiled from various online sources to illustrate current usage of the word 'infectious.' Any opinions expressed in the examples do not represent those of Merriam-Webster or its editors. Send us feedback about these examples.
Word History
1534, in the meaning defined at sense 1a
Phrases Containing infectious
Dictionary Entries Near infectious
Cite this Entry
“Infectious.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/infectious. Accessed 16 Apr. 2024.
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Kids Definition
infectious
adjective
Medical Definition
infectious
adjective
Felix A. Rey
More from Merriam-Webster on infectious
Nglish: Translation of infectious for Spanish Speakers
Britannica English: Translation of infectious for Arabic Speakers
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