infectious

adjective

in·fec·tious | \ in-ˈfek-shəs

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.

Other Words from infectious Synonyms What is the Difference Between contagious and infectious? More Example Sentences Learn More About infectious

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 Fellow senior guard Jalen Marshall, a standout track and field performer who has started the past three years on the hardwood, says his backcourt mate’s play is infectious. — Glenn Graham, baltimoresun.com, 23 Jan. 2022 But Buchan said the antigen tests were about 90 percent effective at picking up cases in people who were most likely to be infectious. — Washington Post, 20 Jan. 2022 Similarly, a study done by the U.K. government itself through its Health Security Agency found that up to 31% of people would still be infectious five days after the onset of COVID symptoms. — Sophie Mellor, Fortune, 17 Jan. 2022 Similarly, testing several days before an event won’t tell you much about who might be infectious on the day of the gathering. — Kaiser Health News, oregonlive, 17 Jan. 2022 Similarly, testing several days before an event won’t tell you much about who might be infectious on the day of the gathering. — al, 16 Jan. 2022 His smile was healing, his hugs the warmest refuge, and his laughter was infectious. — Jen Juneau, PEOPLE.com, 10 Jan. 2022 With Omicron, people were very infectious before a rapid test delivered a positive result, says Blythe Adamson, lead author of the study and founder and chief executive officer of Infectious Economics, a public-health consultancy. — Sumathi Reddy, WSJ, 9 Jan. 2022 His smile was healing, his hugs the warmest refuge, and his laughter was infectious. — Keyaira Boone, Essence, 8 Jan. 2022

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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Dictionary Entries Near infectious

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infectious

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Last Updated

25 Jan 2022

Cite this Entry

“Infectious.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/infectious. Accessed 28 Jan. 2022.

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More Definitions for infectious

infectious

adjective

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

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

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