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 : caused by or resulting from an infection with one or more pathogenic agents infectious mononucleosis — see also infectious disease
c : transmitting or capable of transmitting infection : containing pathogenic agents which may be transmitted infectious droplets
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 At Huntington Memorial Hospital in Pasadena, California, nurses that usually care for one or two patients are now caring for three or four, infectious disease specialist Dr. Kimberly Shriner told CNN on Sunday. Madeline Holcombe, CNN, "Record Covid-19 hospitalizations in US could soon force health experts to ration care," 29 Dec. 2020 People may be getting together in small groups to try to be safe because of the COVID-19 surge, but those interactions can still fuel the spread of the virus, said UCLA infectious disease specialist Dr. Tim Brewer. Los Angeles Times, "A new post-Christmas COVID-19 surge as holidays create ‘viral wildfire’," 27 Dec. 2020 The fact that the monoclonals are authorized for use only on outpatients is a major complication, said Dr. Peter Chin-Hong, an infectious disease specialist at the UCSF School of Medicine. Peter Fimrite, SFChronicle.com, "Shortage of staff, regulations keep monoclonal treatments for COVID on Bay Area hospital shelves," 23 Dec. 2020 Each team is required to have a contact-tracing working group consisting of an infectious disease specialist, team physician, contact tracing officer and contact tracers. Jeff Zillgitt, USA TODAY, "Thunder-Rockets NBA game postponed after three Houston players test positive or inconclusive for COVID-19," 23 Dec. 2020 But the new variant is rapidly replacing other viruses, says Müge Çevik, an infectious disease specialist at the University of St, Andrews. Kai Kupferschmidt, Science | AAAS, "U.K. variant puts spotlight on immunocompromised patients’ role in the COVID-19 pandemic," 23 Dec. 2020 The nine hospitals operated by HealthPartners are among those seeing improvements, said Dr. Mark Sannes, an infectious disease specialist. Christopher Snowbeck Star Tribune, Star Tribune, "Deadly December includes COVID-19 hopes in Minnesota," 19 Dec. 2020 Two of the first UCH team members to receive the vaccine were Dr. Faheem Younus, an infectious disease specialist, and John Haacke, a critical care nurse at Upper Chesapeake Medical Center in Bel Air. S. Wayne Carter Jr., baltimoresun.com, "Frontline workers at Upper Chesapeake Health receive first doses of COVID-19 vaccine," 16 Dec. 2020 Trevor Bedford, an associate professor in the vaccine and infectious disease division of the Fred Hutchinson Cancer Research Center, is also keeping a close eye on the UK variant. Elizabeth Cohen, CNN, "Genetics experts worry coronavirus vaccines might not work quite as well against UK variant," 23 Dec. 2020

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

History and Etymology for infectious

infecti- (in infection) + -ous

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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

20 Jan 2021

Cite this Entry

“Infectious.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/infectious. Accessed 22 Jan. 2021.

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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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Comments on infectious

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