In 1968, some 150 schoolchildren in Norwalk, Ohio became ill with severe viral gastroenteritis that had never been seen before. Four years later, the prototype strain of the virus best known for causing “stomach flu” was identified and named “Norwalk Virus.”
Each new variation was identified by its outbreak location — Snow Mountain, Mexico, Hawaii — until the virulent strains became known as norovirus and the leading cause of gastroenteritis worldwide.
Norovirus has ruined many a cruise trip, family reunion and banquet and continues to be a major problem. Just this month, the Seattle Yacht Club had to temporarily shut down for sanitation after an outbreak of norovirus made 150 guests and employees ill. In Annapolis, about 100 athletes, coaches and spectators reported the classic symptoms of norovirus infection — vomiting, diarrhea, stomach cramps, muscle aches — after attending the Maryland State Swimming Champtionships at the U.S. Naval Academy March 5.
It has been 10 years since the Centers for Disease Control and Prevention’s Morbidity and Mortality Weekly Report provided recommendations for preventing the spread of noroviruses. The drought on control guidance ended last week, when the CDC released its most recent MMWR with a new report titled, “Updated Norovirus Outbreak Management and Disease Prevention Guidelines.”
In the March 4 MMWR, authors from the CDC’s Division of Viral Diseases at the National Center for Immunization and Respiratory Diseases discuss advances in norovirus epidemiology, immunology, diagnostic methods, and infection control that have been made in the last 10 years, and provide recommendations for how norovirus outbreaks can be better detected, reported, and prevented.
The illness caused by norovirus typically occurs 12-48 hours after exposure, and is characterized by acute onset, nonbloody diarrhea, vomiting, nausea, and abdominal cramps. It can be accompanied by low-grade fever and body aches.
It is often described as “mild,” in comparison to other foodborne illnesses, but anyone who has been stricken with norovirus knows that it can cause abject misery.
According to recent estimates, approximately 21 million norovirus cases occur each year in the U.S. The extremely contagious bug is typically transferred from person-to-person or from food or water.
The CDC estimates that one-fourth of norovirus cases are foodborne. Foodborne transmission of noroviruses is typically associated with contamination by infected food handlers during food preparation or service, but can also happen through contamination with human waste. Foods eaten raw, such as leafy greens, fruits and shellfish are the foods most commonly implicated as vehicles for transmission of noroviruses.
Recreational and drinking waters can both be sources of norovirus. Contamination can come from septic tank leakage, sewage, or from breakdowns in municipal water system chlorination. Drinking water and ice have both been identified as the source of norovirus outbreaks.
Person-to-person transmission is common following food- or waterborne outbreaks.
To that end, the CDC report states, “Appropriate hand hygiene is likely the single most important method to prevent norovirus infection and control transmission. Reducing any norovirus present on hands is best accomplished by thorough handwashing with running water and plain or antiseptic soap.”
The authors do not promote the use of hand sanitizers for norovirus control, saying further study is required to determine the efficacy of alcohol-based and other hand sanitizers.
Recommendations for public health professionals “to guide efficient use of public health resources for effective prevention and control of norovirus disease” include:
• Initiating investigations promptly, to facilitate the early detection of the mode of transmission of norovirus and its possible source.
• Promoting good hand hygiene, including frequent washing with soap and running water for a minimum of 20 seconds.
• Excluding ill staff in certain positions, such as foodservice, child-care and patient-care workers, until 48-72 hours after symptoms end.
• Reinforcing effective preventive controls and employee practices to prevent the spread of norovirus.
• Disinfecting potentially contaminated environmental surfaces with a chlorine bleach solution or other Environmental Protection Agency-approved disinfectant.
• Collecting whole stool specimens from at least 5 persons during the acute phase of illness for diagnosis, and reporting results to the CDC through CaliciNet.
• Reporting all outbreaks of acute gastroenteritis to state and local health departments, and to the CDC through the National Outbreak Reporting System (NORS).