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U.S. Department of Health and Human Services


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List of Terms: N

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Did You Know?

Noroviruses are named after the original strain "Norwalk virus," which caused an outbreak of gastroenteritis in a school in Norwalk, Ohio, in 1968. Currently, there are at least four norovirus genogroups (GI, GII, GIII, and GIV), which in turn are divided into at least 20 genetic clusters.


can only sit in food. They can't multiply in food as bacteria do. The viruses is killed by thorough cooking;
survive freezing;
are highly infectious and the body doesn't build immunity to them very well;
resist chlorine and other sewage-treatment agents.


> National Antimicrobial Resistance Monitoring System (NARMS) 
A system that allows the Food and Drug Administration (FDA) to detect when food-borne bacteria - which can cause disease in humans - begin to develop resistance to antimicrobials used in food animals. The program combines the resources of the FDA, the Centers for Disease Control and Prevention (CDC), and the U.S. Department of Agriculture (USDA) to create a nationwide monitoring system.


> National Center for Food Safety and Technology
A consortium of the FDA, Illinois Institute of Technology, and food industry members working together to make food safer for the consumer.


> National Food Safety Education MonthSM (NFSEM)
Founded in 1994 by the International Food Safety Council - a coalition of restaurant and food industry professionals, the month of September is dedicated to focusing public attention on foodborne illness and the Fight BAC!TM campaign's 4 Steps to Food Safety: clean, cook, separate (combat cross-contamination), and chill.
(Also see Fight BAC!TM Campaign.)


> Noroviruses
Noroviruses are a group of viruses (previously known as Norwalk-like viruses) that can affect the stomach and intestines. These viruses can cause people to have gastroenteritis, an inflammation of the stomach and the large intestines. Gastroenteritis is sometimes called a calicivirus infection or food poisoning, even though it may not always be related to food. Norovirus is sometimes called the "stomach flu," although it is not related to the flu (a common respiratory illness cause by the influenza virus). At least 50% of all foodborne outbreaks of gastroenteritis are thought to be attributable to noroviruses. Noroviruses spread extremely easily through food, surfaces such as door handles or other things hands often touch, and aerosolized droplets in the air.

Norwalk Virus
Photo: F.P. Walker, U.S. EPA
Norwalk Virus

Sources: Raw oysters/shellfish, cole slaw, salads, baked goods, frosting, contaminated water and ice, and person-to-person contact.


Incubation: 1 to 2 days after ingestion.

Symptoms: Diarrhea, nausea, vomiting, abdominal pain, headache, and fever.

Duration: 1 to 2 days.


> Nucleic Acid
A polymer substance found in animal and plant cells that holds the genetic information. Two classes of nucleic acids are ribonucleic acid and deoxyribonucleic acid. (Also see Deoxyribonucleic Acid and Ribonucleic Acid.)


> Nucleoid
A circular loop of double-stranded helical deoxyribonucleic acid (DNA) in a cell that is not enclosed in a membrane.

A Nucleoid Structure
Photo: Naomi Ward, Louisiana State University/Biological Sciences
A Nucleoid Structure


> Nucleus (see Cell)