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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

 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 The virus is resilient and can survive for up to three months while staying infectious. — Naseem S. Miller, orlandosentinel.com, "After declaring hepatitis A emergency, state surgeon general stresses hand washing," 2 Aug. 2019 Parents watch after kids are in bed The celebrities appear amid animation, claymation and song — infectious songs. — Sonja Haller, USA TODAY, "Netflix's funny 'StoryBots:' John Legend, Jennifer Garner and other A-listers star in Season 3," 1 Aug. 2019 Qualley praises his generous direction and infectious excitement. — Derek Lawrence, EW.com, "Margaret Qualley knows Once Upon a Time in Hollywood was a 'once-in-a-lifetime experience'," 27 July 2019 The other theory—which Pipitone says is currently most researchers’ favorite—says that clusters of holes are visually similar to rashes or lesions caused by parasitic or infectious diseases. — Natasha Lavender, SELF, "Is Trypophobia Really a Fear of Holes or Something Else Entirely?," 26 July 2019 It can also be contracted when open wounds come into contact with saliva or other potentially infectious material, such as brain or nervous-system tissue, from the animal. — Tom Steele, Dallas News, "Bat at Fort Worth Water Gardens tests positive for rabies, health officials say," 24 July 2019 Measles is a highly infectious respiratory illness that is spread through coughing or sneezing. — Tresa Baldas, Detroit Free Press, "Measles case confirmed in Detroit: Exposure sites, what to know," 19 July 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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