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infectious

adjective
in·​fec·​tious | \ in-ˈfek-shəs How to pronounce infectious (audio) \

Definition of infectious

1a : producing or capable of producing infection bacteria and other infectious agents
b : transmitting or capable of transmitting infection : containing pathogenic agents which may be transmitted infectious droplets
c : caused by or resulting from an infection with one or more pathogenic agents infectious mononucleosis Influenza, malaria, and tetanus are infectious diseases.
2 : spreading or capable of spreading rapidly to others an infectious laugh Her happiness was infectious.
Other Words from infectious Synonyms What is the Difference Between contagious and infectious? More Example Sentences Learn More about infectious

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Other Words from infectious

infectiously adverb
infectiousness noun

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

viruses and other infectious agents She has an infectious grin.

Recent Examples on the Web

 Wearing his signature oversize glasses, Porter relaxes on a couch in a green room after a recent rehearsal, his animated personality and infectious laughter on full, flamboyant display. — Christopher Wallenberg, BostonGlobe.com, "‘Pose’ star Billy Porter is savoring a breakthrough he wasn’t sure would ever happen," 29 Aug. 2019 The big cat is a delicate species, especially susceptible to feline and infectious diseases, the vet said. — CNN, "The ultra-rich are illegally buying cheetahs as pets and it's leading to their extinction," 28 Aug. 2019 Johnson’s infectious moves made the touchdown celebration part of the game, inspiring generations of players to let loose in the end zone, as well as after sacks and other big plays. — The Si Staff, SI.com, "100 Figures Who Shaped the NFL’s First Century," 28 Aug. 2019 In Aurora, a city council committee last week gave preliminary approval to a new city rule that would require the staff of the GEO Group immigration detention facility there to report any infectious disease diagnoses to the fire department. — Elise Schmelzer, The Denver Post, "With growing opposition and slowing prison population growth, what is the future for private prison companies in Colorado?," 25 Aug. 2019 Studies have found that the surfaces of treadmills, weight machines and other typical gym equipment are teeming with bacteria and other infectious germs. — Scott Douglas, sun-sentinel.com, "Your gym is teeming with invisible members: Germs. Here’s how to avoid them.," 29 July 2019 Oftentimes, cancer is caused by infectious viruses such as hepatitis B and human papillomavirus, which can be prevented with a vaccine. — Molly Sullivan, sacbee, "How do you get a skeptical patient to test for cancer? UCD, health center target cultural barriers," 2 June 2018 The Minnesota Board of Animal Health said horses in Otter Tail, Pine and Swift counties have been euthanized since eastern equine encephalitis, equine infectious anemia and West Nile virus were detected. — Forum News Service, Twin Cities, "3 different equine diseases have sickened horses in Minnesota, officials report," 13 Aug. 2019 Five takeaways from the Colorado Rapids infectious offensive outburst against Montreal. — Joe Nguyen, The Denver Post, "“Who is this guy?”: Former Broncos RB Peyton Hillis on how he ended up on the Madden cover," 5 Aug. 2019

These example sentences are selected automatically from various online news sources to reflect current usage of the word 'infectious.' Views expressed in the examples do not represent the opinion of Merriam-Webster or its editors. Send us feedback.

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First Known Use of infectious

1534, in the meaning defined at sense 1a

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More Definitions for infectious

infectious

adjective
How to pronounce infectious (audio)

English Language Learners Definition of infectious

: capable of causing infection
: capable of being passed to someone else by germs that enter the body
: suffering from a disease that can be spread to other people by germs

See the full definition for infectious in the English Language Learners Dictionary

infectious

adjective
in·​fec·​tious | \ in-ˈfek-shəs How to pronounce infectious (audio) \

Kids Definition of infectious

1 : passing from one to another in the form of a germ an infectious illness
2 : easily spread to others an infectious laugh

infectious

adjective
in·​fec·​tious | \ in-ˈfek-shəs How to pronounce infectious (audio) \

Medical Definition of infectious

1 : producing or capable of producing infection bacteria and other infectious agents … virus particles, or virions, are protected within these polyhedra and can remain infectious for years outside cells, even in harsh environmental conditions.— Felix A. Rey
2 : transmitting or capable of transmitting infection : containing pathogenic agents which may be transmitted infectious droplets
3 : caused by or resulting from an infection with one or more pathogenic agents infectious mononucleosis — see infectious disease

Other Words from infectious

infectiously adverb
infectiousness noun

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