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
Perry Vandell, The Arizona Republic, 5 Nov. 2024
What Causes Chronic Wasting Disease? CWD is caused by infectious proteins called prions.
—Jake Parks, Discover Magazine, 5 Nov. 2024
Her infectious energy and unwavering support for her squad and peers create an encouraging environment that brings out the best in everyone around her.
—Caroline Beck, The Indianapolis Star, 4 Nov. 2024
The virus is not spread through casual contact such as hugging, shaking hands or through the air, and patients are not believed to be infectious before symptoms begin.
—Nathaniel Weixel, The Hill, 29 Oct. 2024
See all Example Sentences for infectious 
Dictionary Entries Near infectious
Cite this Entry
“Infectious.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/infectious. Accessed 23 Nov. 2024.
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infectious
adjective
Medical Definition
infectious
adjective
Felix A. Rey
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