Preventing the Spread of Norovirus

What Is Norovirus?

Norovirus is a highly contagious virus that is responsible for gastroenteritis (inflammation of the intestines) in humans that is usually referred to as a norovirus infection. The specific virus responsible for causing illness in humans is the Norwalk virus, which is part of the Norovirus group. Norovirus is also referred to as the stomach flu or winter vomiting bug. It is responsible for a considerable number of inpatient and outpatient visits every year.

Norovirus Symptoms

Norovirus infection results in inflammation of the intestinal tract, which can result in sudden onset of severe diarrhea and vomiting. Some people also experience pain or cramps in the abdominal region, low-grade fever, muscle aches and pains, general feelings of discomfort, and nausea. In some cases extreme dehydration may result. In most people, symptoms last between one and three days, but traces of norovirus can remain in fecal deposits for up to several weeks or even months. Some carriers of the virus are asymptomatic (showing no common signs or symptoms of the pathogen) but are still contagious.¹

How Contagious Is Norovirus?

As few as 18 particles of the virus are needed to spread the pathogen to another person, making it extremely contagious.² This explains its ability to spread quickly, especially in closed environments such as schools, colleges, day-care centers, cruise ships and prisons. Individuals are most contagious when they are symptomatic and during the three days after recovery.

Norovirus Incubation Period

The incubation period refers to the time between first exposure to a virus or infection and the appearance of symptoms commonly associated with the virus. According to the Centers for Disease Control and Prevention (CDC), the incubation period after exposure to norovirus is 12 to 48 hours, with the average period being around 33 hours.²

Who Is at Risk?

Everyone is at risk of norovirus, but the elderly, infants and people already experiencing acute or chronic comorbidities are at increased risk. Elderly patients in long-term care facilities are particularly at risk if a norovirus outbreak occurs due to general decreased strength and ability to fight off disease and illness. Patients with compromised immune systems, such as those undergoing chemotherapy or organ transplant, or those with a coinfection resulting from HIV, are also at increased risk. Immunosuppressed patients are unable to recover as quickly from norovirus, in some cases developing chronic symptoms that persist for weeks to years.³

How Is Norovirus Diagnosed?

A clinical diagnosis based on signs and symptoms usually determines whether a patient has norovirus. In outbreak situations, when the source of the outbreak needs to be determined, norovirus can be detected by measuring levels of viral RNA in fecal specimens from infected patients using a reverse transcription-polymerase chain reaction (RT-PCR) assay. This assay is available at most state public health laboratories.²

There is no recommended treatment for norovirus illness other than rest and hydration. Antibiotics are not effective, as norovirus is not a bacterium. Recovery time depends on the strength of the patient’s immune system, but for most healthy adults the virus will finish running its course within a few days. It is important to recover the liquids lost during this period due to the dehydration caused by diarrhea and vomiting. In patients unable to sufficiently replace their levels of hydration by drinking liquids, intravenous fluid rehydration might be required.

The CDC estimates that norovirus is responsible for 19 million to 21 million cases of gastroenteritis annually in the U.S. Almost 2 million people seek outpatient treatment, and a further 400,000 seek treatment at hospital emergency rooms. Annually, 56,000–71,000 people are hospitalized, resulting in 570-800 deaths.⁴ Although norovirus infections tend to peak during the winter season, they are common throughout the year. Additionally, new strains of the virus that emerge can result in significant increases in reported illnesses.

Between 2009 and 2012, almost 3,500 outbreaks were reported to the CDC’s National Outbreak Reporting System. Of those, 63% were in healthcare settings, with the overwhelming majority of those outbreaks occurring in long-term care facilities and nursing homes. Restaurants and banqueting facilities accounted for 22% of all outbreaks, while 6% occurred in schools.⁵

Norovirus is shed in the stool (feces) and vomit of infected people. Transmission usually results from the accidental ingestion of contaminated feces and vomit. This can occur in several ways:

Contact with surfaces contaminated with infected stool or vomit particles: The transmission of norovirus via inanimate objects such as shared medical equipment, computers and mobile devices puts the general public at risk. This is especially true in locations such as hospitals, nursing homes, schools, colleges and cruise ships. Transmission through contaminated surfaces also increases the risk of infection for healthcare providers who care for infected patients, and for environmental service workers and custodians who clean and disinfect during an outbreak.

Contact with contaminated food and water: This can occur in restaurants and communal eating areas where an infected worker has contaminated food and water that is then ingested by customers. Food may also be contaminated at any point, such as during its growing, processing or preparation. Foods that are commonly responsible for outbreaks include leafy greens, fresh fruits and shellfish, particularly oysters.

The Role of Surfaces in the Spread of Norovirus

Hard surfaces play a particularly important role in the transmission of norovirus. Studies have shown that the virus can persist in a dormant state on steel, wood, ceramic, plastic and glass for up to 28 days.⁶ The long persistence means that transmission may still occur long after a surface is contaminated. Only a small amount of the highly contagious virus needs to be transmitted to cause an infection.

The rapid spread of norovirus was shown by the results of a study that assessed the ability of hands and cloths to spread norovirus-contaminated fecal material to other hand-contact surfaces, such as faucets, door handles and phones.⁷ The study showed that contaminated hands could transfer the virus to up to seven otherwise clean surfaces that hands often touch. Another study used a harmless surrogate virus to mimic the spread of norovirus in an office building. At the beginning of the day, the surrogate was placed on common surfaces such as doorknobs and tabletops. After several hours, the hands of 40-60% of office workers had become contaminated. Many other commonly touched surfaces were also contaminated within a short period of time.⁸5. Preventing the Spread of Norovirus

Measures to prevent the spread of norovirus correspond to the ways the virus can be transmitted. CDC guidelines issued in 2011 make five recommendations: hand hygiene, cleaning and disinfection of surfaces, thorough cooking of food, not preparing food when sick, and correctly washing soiled laundry. Two of the most important recommendations are cleaning and disinfection and hand hygiene.

Cleaning and Disinfection

Correct and thorough cleaning and disinfection of hard surfaces is critical to preventing the transmission of norovirus. Surfaces should be regularly cleaned and disinfected with an EPA-registered disinfectant with approved claims against norovirus. In general surfaces should be cleaned first to remove visible organic material such as contaminated feces and vomit, and then disinfected. Once the disinfectant has been applied, it should be allowed to remain wet on the surface for the appropriate contact time. The contact time, also known as the wet or dwell time, is the time the surface must stay visibly wet with the disinfecting solution in order for it to be effective against norovirus. The product label will specify the contact time, which can range from 30 seconds to 10 minutes, depending on the disinfectant.

Some disinfectants containing quaternary ammonium chlorides as the antimicrobial ingredients may be effective against norovirus. Hydrogen peroxide-containing disinfectants are often more effective than quaternary ammonium chlorides. However, the CDC commonly recommends a sodium hypochlorite (bleach) product, since bleach is considered the most effective disinfecting agent in norovirus outbreak situations. The CDC recommends using a solution of 1,000–5,000 ppm household bleach, made by adding 5–25 tablespoons of household bleach (5.25%) to one gallon of water (equivalent to a 1:50 or 1:10 dilution) or any other disinfectant registered as effective against norovirus by the EPA. Users should always follow the product label’s directions for use if the product is registered against norovirus. 

Studies have documented the effectiveness of cleaning and disinfection to reduce norovirus load on surfaces and combat outbreaks. In the study that demonstrated the spread of norovirus on surfaces, bleach was the only disinfectant that completely eliminated norovirus from surfaces. It did so only after the surface was first cleaned to remove organic soil.⁷ The study also showed that use of a detergent that visibly cleaned surfaces did not inactivate norovirus but rather spread the virus on the surfaces. In a hospital outbreak that affected 90 patients and 265 healthcare workers, a multi-strategy approach that included disinfecting with a 1:50 dilution of bleach was required to terminate the outbreak.⁹

Hand Hygiene

Hands should be washed vigorously with soap and warm water for more than 20 seconds and at the following times:

The CDC recommends cleaning and disinfecting contaminated surfaces using an EPA-registered disinfectant effective against norovirus. The following Clorox Healthcare and CloroxPro products have EPA-approved claims against norovirus. Always follow the label’s directions for use when cleaning and disinfecting.