Prevention and control

by Kirsten M. Thompson and Ruth L. Petran

Background

Noroviruses (previously known as Norwalk-like viruses) are widely known for causing outbreaks of illness among large numbers of people on cruise ships. Since the original Norwalk virus was identified in 1968, there has been increasing recognition of norovirus as an agent of viral gastroenteritis traced to restaurants and catered meals, nursing homes, schools and camps. The Centers for Disease Control and Prevention (CDC) estimate that at least 50 percent of foodborne outbreaks in the United States are attributed to norovirus.¹ Of that, 60 percent occur in restaurants and banquet facilities, 9 percent in private homes, 8 percent in the workplace, 4 percent in schools, and 2 percent in healthcare settings. The remaining cases occurred in camps, churches/temples, fairs, festivals, picnics, and in prison/jails. ²

In global terms, the number of norovirus infections is increasing drastically and becoming a common cause of gastroenteritis outbreaks in Europe³ and other countries. Epidemic-like outbreaks in hospitals and long term care facilities are being seen more and more frequently, and have the longest duration in healthcare settings with the median length of outbreak of 19 days in hospitals and 16 days in nursing homes. In non-healthcare settings outbreaks were significantly shorter, with an average outbreak lasting 7 days. ⁴

There are three important reasons for controlling norovirus outbreaks in healthcare settings. First, norovirus infection prolongs hospital stay and causes complications in compromised individuals. Second, outbreaks are costly—particularly with the added cost of cleaning and disinfection, the cost of a healthcare-associated infection and staff absenteeism. Finally, some patients may develop chronic infections which facilitate mutation in the virus, perpetuating the cycle of infection. ⁵

Symptoms and Disease Process

Noroviruses are members of the Calicivirus family. The first norovirus was discovered in the city of Norwalk, Ohio, which is why they were previously called “Norwalk viruses.” Noroviruses are uncoated RNA viruses, approximately 26 to 35 nm in size, and their only known reservoir is the human body. Noroviruses are reported to be the second most frequent cause of acute gastrointestinal infections, ⁶ the symptoms of which include nausea, frequent and violent vomiting, and diarrhea. Other symptoms include low-grade fevers, chills, headaches, muscle aches and fatigue. Onset occurs in as little as 12 hours from exposure, but commonly takes 24 to 48 hours after ingesting the virus. The illness usually lasts one to two days, and in most cases recovery occurs without problems unless the person becomes dehydrated from the illness.

Noroviruses are extremely infectious. As few as 10 to 100 virus particles are sufficient to trigger an infection. After the outbreak of the illness, the pathogens can be detected in high numbers in both the stool and vomit of patients. One gram of stool can contain up to 100 billion virus particles. ⁷

Treatment of norovirus infection depends on the symptoms and primarily involves compensating the enormous loss of fluid and electrolytes. There are presently no vaccines to prevent infections and no antiviral medicines available that treat norovirus infection. After an infection, the body is often immune to the pathogen for just a very short period of approximately eight weeks.

Primary Routes of Transmission

Because noroviruses in very high levels (millions per gram), are present in the stool or vomit of infected people it is essential that ill people are prohibited from handling food. Most foodborne outbreaks of norovirus illness are likely caused by direct contamination of food by a food handler before its consumption. Norovirus particles can also be carried by aerosols over distances longer than three feet to land on surfaces. ⁸ Others may become ill by touching these contaminated surfaces and then touching their mouths, or having direct contact with an infected person. Many outbreaks in long term care facilities are preceded by illness among food handlers, suggesting that these outbreaks may initially be caused by foodborne transmission.⁹

Outbreaks have frequently been associated with consumption of ready-to-eat foods, including various salads, sandwiches and bakery products. Liquid items such as salad dressing or cake icing that allow the virus to mix evenly have also been implicated as a source of outbreaks. Additionally, food can be contaminated at its source, for example oysters from contaminated waters, which have been associated with widespread outbreaks of gastroenteritis. Other foods, including raspberries and salads, have been contaminated before widespread distribution and subsequently caused extensive outbreaks. ¹⁰

Noroviruses have very high resistance levels and can remain infective for several months in a healthcare environment. ¹¹ Both this high resistance to environmental conditions and the small amount needed for an infection may explain how it spreads so quickly and widely. A large norovirus outbreak impacted more than 1,000 people in the Houston Astrodome when it housed Hurricane Katrina evacuees. Inadequate sanitary conditions, the lack of adequate hand-washing facilities, delays in cleaning and decontaminating soiled areas and bedding, and close proximity of people contributed to the spread.¹²

Norovirus is especially active in the winter months. The reasons for this seasonal increase are still not clear. One possible reason is that the pathogens benefit from the low average temperatures and low air humidity in the winter months. Another possible significant factor is the decreased sunlight, which can affect both the environmental stability of the pathogen and the immune status of human beings. It could also be that in colder climates people stay indoors in closer contact, a situation which encourages the spread of infection.

Detection and Testing

Norovirus cannot be detected by standard culture methods, but only by more complex techniques such as microscopic examination or by polymerase chain reaction. As the pathogen cannot be reproduced in laboratory animals or cell cultures, it is not possible to carry out efficacy tests on human noroviruses so feline calicivirus (a disease-causing pathogen in cats) is often used as a surrogate virus for testing microbiocides effective against it. Still, the level of reduction required for efficacy, generally speaking 99.99 percent for many pathogens, is not sufficient in the case of norovirus due to the low infection dose and high concentration of the pathogen in stool. As the effectiveness of the norovirus cannot be verified directly on the pathogen, appropriate safety margins must be taken into consideration when disinfecting hands, surfaces or other objects. In fact, the United States Food and Drug Administration (FDA) has not recognized a viral efficacy test method for hand hygiene products, so no norovirus claims are allowed on hand soaps or hand sanitizers sold in the U.S. market at this time.

Prevention

The excretion of large numbers of the virus in stool and vomit, the high infectivity and environmental resistance of the pathogen, and the lack of long-term immunity favor the rapid spread of a norovirus infection in healthcare facilities in particular. It is therefore important that facilities and institutions follow proper hygienic protocols, particularly with respect to environmental and hand hygiene. When preparing meals, care must be taken to ensure that foods such as meat and seafood are well cooked, rendering potential pathogens harmless.

If an outbreak of the infection occurs despite all precautionary measures, the first priority is to break the chain of infection at an early stage—only in this way can the continued spread of the illness be avoided. Everyone employed in a healthcare facility should therefore be well informed about the spread of norovirus infections and the correct way to deal with infected patients. Staff training programs can supply the necessary know-how in this respect.

Control

The primary control of norovirus relies on the exclusion of ill individuals from patient care, food and hospitality settings. Food handlers who have recently recovered from norovirus illness should be given non-food handling tasks and non patient care duties.

If an outbreak of a norovirus infection occurs, devices, surfaces and hands must be cleansed and disinfected particularly carefully. At least once a day, it is necessary to scrub, wash and disinfect all surfaces such as bedrails, bedside tables, door handles that a norovirus patient comes into contact with. Toilets and bathrooms are especially critical areas and require the highest standards of hygiene. Several studies cite the association of norovirus with high touch surfaces such as toilet handles, door handles, patient equipment, elevator buttons, switches and telephones. When fingers come into contact with virus-contaminated material, norovirus is consistently transferred to typical high touch surfaces or objects. ¹³

Normal cleaning and sanitizing procedures are typically not sufficient to inactivate the virus; rather, aggressive disinfection protocols are needed. Prompt attention to disinfection is needed to reduce the magnitude of norovirus outbreaks. For cleanup of vomit or other body excretions, personal protection equipment and a biohazard clean-up kit is very useful to minimize further spread of the virus.

Measures to limit transmission: ¹⁴

1. Patients with suspected norovirus infection should be managed with Standard Precautions; however, Contact Precautions should be used when caring for diapered or incontinent persons or during outbreaks. Group symptomatic patients and provide separate toilet facilities for ill and well persons. Instruct visitors on appropriate hand hygiene and monitor compliance with contact isolation precautions.
2. Practice good hand hygiene. Hand hygiene is critical to help prevent and control of virus outbreaks. This is a primary transmission mode and must be judiciously implemented. Washing well and often is the best control.

• Wash hands frequently with soap and water: ¹⁵
  • Wet hands first with water.
  • Apply manufacturer-recommended amount of product to hands.
  • Rub hands together vigorously for at least 15 seconds, covering all surfaces of the hands and fingers.
  • Rinse hands with water and dry thoroughly with a disposable towel.
  • Use towel to turn off the faucet.
• Alcohol-based sanitizing hand gels (> 62% ethanol content) may be used to complement hand washing with soap and water.
  • When decontaminating hands with an alcohol-based hand rub, apply product to palm of one hand and rub hands together, covering all surfaces of hands and fingers, until hands are dry.

1. Disinfect contaminated surfaces with either chlorine bleach at 1000 to 5000 ppm or a disinfectant registered as effective against norovirus by the Environmental Protection Agency in accordance with the manufacturers’ instructions. A list of EPA-approved products is available at http://www.epa.gov/oppad001/list_g_norovirus.pdf. Persons cleaning areas heavily contaminated with vomit or stool should wear surgical masks as well.

           In general:

• Cover material with tissue or paper toweling until clean-up detail arrives.
• Wear disposable gloves and face mask when cleaning the spill.
• Follow biohazard clean-up kit instructions:
  • Sprinkle adsorbent material on body fluids.
  • Pick up with scoop and place in disposal bag.
• Apply a properly registered disinfectant per label instructions.
• Wash hands thoroughly after removing protective equipment.

1.  Affected staff should not return to work until 24 to 72 hours after symptoms resolve and practice good hand hygiene after returning. Avoid sharing staff members between units or facilities with affected patients and units or facilities that are not affected. Close affected units to new admissions and transfers.
2.  Food items that may have become contaminated with norovirus should be immediately discarded. The virus does not multiply in foods or in the environment, but can persist on contaminated surfaces and survives freezing. Norovirus is also relatively heat stable, though cooking foods to 70°C (158°F) for five minutes or boiling for one minute was shown to destroy feline calicivirus, ¹⁶ the surrogate for norovirus.

References

1. CDC. 2009. Surveillance for Foodborne Disease Outbreaks—United States, 2006. MMWR 58(22);609-615. http://www.cdc.gov/mmwr/preview/mmwrhtml/mm5822a1.htm.
2. CDC. OutbreakNet Foodborne Outbreak Database Search Tool  http://wwwn.cdc.gov/foodborneoutbreaks/Default.aspx (accessed 10/2/09).
3. Lopman BA, Reacher MH, van Duijnhoven Y, Hanon F-X, Brown D, Koopmans M. Viral gastroenteritis outbreaks in Europe, 1995-2000. Emerg Infect Dis. 2003 Jan.
4. Harris JP, Lopman BA, O’brien SJ.  Infection control measures for Norovirus: a systematic review of outbreaks in semi-enclosed settings  Journal of Hospital Infection (2010) 74, 1-9.
5. Koopmans M. Noroviruses in healthcare setting: a challenging problem. Journal of Hospital Infection (2009) 73, 331-337.
6. Patel, et. al 2008 Emerg Infect Dis 14(8):1224-1231.
7. Atmar, et.al. 2008. Norwalk virus shedding after experimental human infection. Emerging Ingectious Disease 14:1553-7.
8. Siegel JD, Rhinehart E, Jackson M, Chiarello L, and the Healthcare Infection Control Practices Advisory Committee, 2007. Guideline for Isolation Precautions: Preventing Transmission of Infectious Agents in Healthcare Settings, June 2007. http://www.cdc.gov/ncidod/dhqp/pdf/isolation2007.pdf
9. MMWR August 24, 2007/56(33); 842-846 Norovirus Activity – United States, 2006 – 2007.
10. MMWR, June 2001; Vol. 50, No. RR-9:1-18.
11. Cheesbrough, et.al. 2000. Epidemiol. Infect. 125:93-98.
12. MMWR, Oct 14, 2005; Vol 54(40);1016-1018.
13. Dancer SJ. The role of environmental cleaning in the control of hospital-acquired infection. Journal of Hospital Infection (2009) 73, 378-385.
14. CDC Norovirus in Healthcare Facilities – Fact Sheet released December 21, 2006: http://www.cdc.gov/ncidod/dhqp/id_norovirusFS.html
15. Centers for Disease Control and Prevention. Guideline for Hand Hygiene in Health-Care Settings: Recommendations of the Healthcare Infection Control Practices Advisory Committee and the HICPAC/SHEA/APIC/IDSA Hand Hygiene Task Force. MMWR 2002;51(No. RR-16).
16. Doultree, J.D., J.D. Cruce, C.J. Birch, D.S. Bowen, and J.A. 1999. Marshall. Inactivation of Feline Calicivirus, a Norwalk virus surrogate. Journal of Hospital Infection 41:51-57.

Kirsten Thompson is a senior program leader with Ecolab Healthcare. She frequently writes on the topic of hand hygiene and infection control. Thompson can be reached at kirsten.thompson@ecolab.com.

Ruth Petran is a scientist at Ecolab specializing in Food Safety. She can be reached at ruth.petran@ecolab.com.