Abstract & Commentary
Norovirus It's Here to Stay
By Stan Deresinski, MD, FACP, FIDSA, Clinical Professor of Medicine, Stanford, Associate Chief of Infectious Diseases, Santa Clara Valley Medical Center, is Editor for Infectious Disease Alert.
Synopsis: Noroviruses are the major single cause of gastroenteritis outbreaks throughout the world and the leading cause of foodborne disease in the United States.
Source: Centers for Disease Control and Prevention. Updated Norovirus Outbreak Management and Disease Prevention Guidelines Recommendations and Reports. Morb Mortal Wkly Rep 2011;60(RR03):1-15. Available at http://cdc.gov/mmwr/preview/mmwrhtml/rr6003a1.htm?s_cid=rr6003a1_w. Accessed March 14, 2011.
Ten years after their original publication, the Centers for Disease Control and Prevention (CDC) has updated their recommendations for the prevention of norovirus infection and the management of outbreaks due to this non-enveloped, single-stranded RNA member of the Calciviridae family. Since 2001, a single norovirus genotype GII.4 has emerged as the major cause of infections throughout the world. Its emergence is evidence of the ability of the virus to evolve in response to the selective pressure of host immune systems, thus allowing its escape from immune suppression. The success of this virus is also the result of the fact that prior exposure to the virus does not provide lasting protection. While pre-existing homologous antibody is protective, this protection appears to be lost after 2-6 months. These facts, combined with an estimated infectious dose as low as 18 virions when a gram of feces collected during the period of peak viral shedding is estimated to contain 5 billion infectious doses help frame the problem. To make matters worse, while peak shedding is reached 2-5 days after symptom onset, viral excretion persists during and after convalescence, lasting for an average of 4 weeks after infection. In addition, as many as approximately one-third of infections are asymptomatic and, while such infections are associated with lower levels of fecal shedding, the very small infectious dose necessary for transmission makes these asymptomatic individuals a potential source of transmission.
Noroviruses are the predominant cause of outbreaks of gastroenteritis throughout the world, being responsible for approximately one-half of those investigated in Europe and the United States. In the United States, approximately one-third of norovirus outbreaks occurred in long-term care facilities, another approximately one-third were from restaurants, parties, and events, and one-fifth were vacation-related, including cruise ships. Thirteen percent arose in schools and communities. Noroviruses are the leading cause of foodborne disease outbreaks in the United States.
The preferred diagnostic method for diagnosis of norovirus infection is reverse transcriptase (RT)-PCR of stool or vomitus. While some laboratories offer such testing, there is no FDA-approved commercial kit for this purpose.
CDC recommendations for investigation and response to norovirus outbreaks in any setting, including acute and long-term care facilities, are as follows:
- Initiate investigations promptly, including collection of clinical and epidemiologic information, to help identify predominant mode of transmission and possible source.
- Promote good hand hygiene, including frequent washing with soap and running water for a minimum of 20 seconds. If available, alcohol-based hand sanitizers (≥ 70% ethanol) can be used as an adjunct in between proper handwashings, but should not be considered a substitute for soap and water handwashing.
- Exclude ill staff in certain positions (e.g., food, child care, and patient care workers) until 48-72 hours after symptom resolution. In closed or institutional settings (e.g., long-term care facilities, hospitals, and cruise ships), isolate ill residents, patients, and passengers until 24-48 hours after symptom resolution. In licensed food establishments, approval from the local regulatory authority might be necessary before reinstating a food employee following a required exclusion.
- Reinforce effective preventive controls and employee practices (e.g., elimination of bare-hand contact with ready-to-eat foods and proper cleaning and sanitizing of equipment and surfaces).
- After initial cleaning to remove soiling, disinfect potentially contaminated environmental surfaces using a chlorine bleach solution with a concentration of 1,000-5,000 ppm (1:50-1:10 dilution of household bleach [5.25%]) or other Environmental Protection Agency (EPA)-approved disinfectant. In health care settings, cleaning products and disinfectants should be EPA-registered and have label claims for use in health care; personnel performing environmental services should adhere to the manufacturer's instructions for dilution, application, and contact time.
- Collect whole stool specimens from at least five persons during the acute phase of illness (≤ 72 hours from onset) for diagnosis by TaqMan-based real-time RT-PCR, perform genotyping on norovirus-positive stool specimens, and report results to CDC via CaliciNet (CDC's electronic norovirus outbreak surveillance network).
- Report all outbreaks of acute gastroenteritis to state and local health departments, in accordance with local regulations, and to the CDC via the National Outbreak Reporting System.