Noroviruses are tiny, intracellular organisms that consist of a single-stranded RNA genome. The viruses are classified into six different subgroups, designated GI through GVI. Of these subgroups, GI and GII comprise the majority of norovirus infections in humans. GI and GII norovirus subtypes contain approximately 30 distinctly identifiable variations of the virus.

In the United States, the norovirus is the main cause of foodborne illness, leading to more than 21 million cases of acute gastroenteritis, over 70,000 hospitalizations, and close to 800 deaths annually. In developing nations, the statistics are far worse, particularly for children under the age of 5, who die from the virus at a rate of nearly 200,000 per year.

Public health researchers often consider the norovirus to be the perfect human pathogen. It is highly contagious and rapidly evolving, and while unpleasant, it doesn’t usually incapacitate its hosts, thus allowing them to move around and infect even more people. Most individuals who fall ill with norovirus feel better within a few days; yet they can transmit the virus days and even weeks following their recovery.

This article discusses the unique characteristics of the norovirus, including its transmission methods, the symptoms of infection, and ways to treat the illness.


Viruses are the smallest microbes in existence, ranging in size from a couple dozen to approximately 1,000 nanometers. However, noroviruses are extremely tiny, even by virus standards, measuring just 27 nanometers.

The insignificant size of noroviruses is in stark contrast to their hardiness. Their potent chemical makeup, rapid evolution, and environmental resistance make them a unique pathogen.

For example, the virus has one of the lowest dosage requirements for infection (≥ 18 particles) of all viral agents in nature. The virus is also actively present at remarkably prolific levels—an estimated 5 billion infectious doses per gram of feces. In addition, the chemical makeup of the norovirus is unusually stable, thus enabling it to withstand environmental conditions that would eradicate the vast majority of potential contaminants.

Because of its inherent chemical stability, the norovirus can tolerate wide temperature ranges, thereby increasing the length of time in which it can cross-contaminate—up to two weeks on most surfaces. The norovirus has also demonstrated resistance to most types of chemical disinfectants, which many people heavily rely upon to avoid illness.


The norovirus is among the most contagious viruses in existence. As a consequence, most people over the course of their lifetimes will contract some type of norovirus infection. Citizens of the United Kingdom (UK), for example, often acquire a variation of norovirus sickness during the winter months. The virus is so commonplace, that locals simply call it the “winter vomiting bug.” The country is one among many that consider norovirus to be a public health concern.

There are numerous ways that one can acquire the norovirus. The most common means of transmission are: consuming contaminated food or drink, providing care to someone who is ill, touching contaminated surfaces, and shaking hands. Most often, the virus spreads when an individual comes into contact with contaminated feces or vomit and then touches his or her mouth. Other, less-common methods of transmission also exist.

The virus’s ability to rapidly evolve is also problematic for containment efforts. This trait applies to all known subtypes of norovirus. As a result, it is difficult for public health officials to apply a comprehensive prevention and treatment framework (e.g. routine treatment protocols during flu season).


The norovirus affects populations across the world. In English-speaking countries, the virus is simply named “the stomach flu” or “stomach bug.” The most common symptoms associated with norovirus include abdominal pain and/or cramps, mild fever, muscle pain, nausea, vomiting, and loose stools or diarrhea.

Most often, symptoms will surface 24 to 48 hours after exposure and last up to three days. In rare cases, the virus can cause severe dehydration, the symptoms of which include dry mouth, dizziness, fatigue, listlessness, and decreased urine production.


Most people stricken with norovirus are able to recover without medical intervention. For many, rest, hydration, and over-the-counter medications (if desired) are sufficient for self-treatment.

While in most cases, the virus will simply regress and not become life-threatening, at-risk patients, such as immunocompromised adults, young children, and the elderly, can experience serious health complications. Babies, especially, are more prone to dehydration due to their small stature and underdeveloped organs.