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.

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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 Earlier this year, McCaul championed the Global Health Fund, which raises money to eradicate infectious diseases worldwide. Claire Goodman, Houston Chronicle, "Rep. McCaul’s Global Hope Act brings lifesaving cancer treatments to children in developing nations," 3 Jan. 2020 Noelle has an infectious smile that stretches super wide. oregonlive, "Mikayla Pivec’s Oregon State women’s basketball diary: Thanksgiving on the road, extreme couponing habits, what her Beaver teammates are like," 16 Dec. 2019 He will be remembered for his easy-going manner, his infectious ever-present smile and his beautiful light brown eyes. courant.com, "Kurran A. Rai," 17 Nov. 2019 The new numbers, though still conservative, underscore the magnitude of the problem and will help prioritize resources to address the most pressing threats, infectious disease experts said. Anchorage Daily News, "Deadly superbugs pose greater threat than previously estimated," 13 Nov. 2019 But the results are another good reason to immunize children against the virus, the studies' authors and other infectious disease experts say. Eva Frederick, Science | AAAS, "How measles causes the body to ‘forget’ past infections by other microbes," 31 Oct. 2019 No humans have ever become infected, although some public health groups recommend not eating meat from an infected deer because some infectious disease experts believe the disease could someday jump to people. Dave Orrick, Twin Cities, "Chronic wasting fears force DNR to ‘scramble’ over deer carcass disposal in some areas," 29 Oct. 2019 Health care providers often treat these symptoms as little more than annoying side effects of having an infectious disease. Joshua Schrock, The Conversation, "Feeling sick is an emotion meant to help you get better faster," 17 Dec. 2019 To make the matter worse, no one knows why, prompting investigations into everything from infectious diseases to climate change to water pollution. Carrie Arnold, National Geographic, "A freshwater mussel apocalypse is underway—and no one knows why.," 16 Dec. 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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Time Traveler for infectious

Time Traveler

The first known use of infectious was in 1534

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Statistics for infectious

Last Updated

7 Jan 2020

Cite this Entry

“Infectious.” The Merriam-Webster.com Dictionary, Merriam-Webster Inc., https://www.merriam-webster.com/dictionary/infectious. Accessed 20 January 2020.

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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

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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