infectious

adjective in·fec·tious \ in-ˈfek-shəs \

|Updated on: 22 Jul 2018

Examples: infectious in a Sentence

Editor's Note: What is the Difference Between contagious and infectious?

Definition of infectious

1 a : capable of causing infection

viruses and other infectious agents

b : communicable by infection

an infectious disease

— compare contagious

2 : that corrupts or contaminates

3 : spreading or capable of spreading rapidly to others

their enthusiasm was infectious

an infectious grin

—

infectiously

adverb

—

infectiousness

noun

See infectious defined for English-language learners

See infectious defined for kids

Examples of infectious in a Sentence

viruses and other infectious agents
She has an infectious grin.

Recent Examples of infectious from the Web

Depending on the situation at hand, your doctor may decide to administer what’s called a prophylaxis against Lyme disease, Luis Marcos, M.D., the fellowship program director at Stony Brook Medicine’s division of infectious diseases, tells SELF.

— kate sheridan, SELF, "Here’s Exactly What to Do if a Tick Bites You," 14 July 2018
Around 75 percent of today’s emerging infectious diseases are zoonotic, or transferred by contact between wildlife and humans.

— katherine j. wu, Smithsonian, "A Never-Before-Seen Virus Has Been Detected in Myanmar’s Bats," 11 July 2018
The hospital has sent the boys’ blood samples to a Bangkok laboratory that specializes in emerging infectious diseases.

— New York Times, "Freed From Thai Cave, Boys May Still Face Health Problems," 10 July 2018
Experts say the boys could be coping with a variety of medical problems stemming from their weeks trapped in the cave, such as exposure to infectious diseases, low oxygen, cold temperatures and food deprivation.

— deborah netburn, latimes.com, "What health risks will the Thai soccer players face after they're rescued from the cave?," 10 July 2018
An additional, smaller waiting room is designated for patients with an infectious disease.

— yadira sanchez olson, Lake County News-Sun, "New county health center in Zion designed to meet 'the unmet needs of patients'," 9 July 2018
Sam Telford, a professor of infectious disease and global health at Tufts University, helped discover the mechanism that led to the development of Lymerix and ran one of the clinical trials that tested it.

— sumathi reddy, WSJ, "New Effort for Lyme Disease Vaccine Draws Early Fire," 9 July 2018
Valley fever is one of the most commonly reported infectious diseases in Arizona, and of those cases, 94 percent are in Maricopa, Pima and Pinal counties, all desert areas.

— nathan j. fish, azcentral, "Another dust-storm season, another reminder about valley fever," 6 July 2018
Doctors, nurses and mental health specialists are on call to treat trauma, organ failure and infectious disease in the event that anyone is found alive.

— Time, "A Youth Soccer Team Has Been Trapped in a Thai Cave for More Than a Week. Here's Why It's Taking So Long to Find Them," 2 July 2018

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.

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.