Norwalk Viruses Here Since Man Has Been On the Planet


Barry Inman

Barry Inman

Noroviruses: The Virus That Won’t Quit

Acute infectious gastroenteritis, also commonly referred to as the “stomach flu” (although it is not at all related to influenza), is an extremely common illness long suspected to be caused by viruses, but only in the past three decades have these viruses been identified.

Among the most common are the Noroviruses, also called Norwalk-like viruses (NLVs), which have probably been around since man has been on the planet. In the early 1900s, it was referred to as “winter vomiting disease” and later also called, “epidemic viral gastroenteritis”, “acute infectious nonbacterial gastroenteritis,” and the list goes on.

For many years though, it has remained under the radar for most clinicians, because it does not grow in culture and as humans are the only host, there is no animal model to study.

NOROVIRUSES are a group of viruses that cause acute gastroenteritis in humans. Norovirus was recently approved as the official genus name for the group of viruses provisionally described as “Norwalk-like viruses” (NLV).

NOROVIRUSES are a group of viruses that cause acute gastroenteritis in humans. Norovirus was recently approved as the official genus name for the group of viruses provisionally described as “Norwalk-like viruses” (NLV).

In the 1940s it was demonstrated that pooled stool obtained from patients in an institutional outbreak of a nonbacterial gastroenteritis could infect exposed volunteers.  Then in 1968, the Center for Disease Control (CDC) investigated an elementary school outbreak of vomiting disease where half of the students and teachers developed symptoms, in Norwalk, Ohio, giving the virus its name.

Later, the specific virus was finally identified using immune electron microscopy to distinguish the viral particles in stools of infected volunteers.  And it was only in the recent 1990s through molecular laboratory techniques, that it has become easier to identify these agents.  In fact, in 1996, the CDC was able to finally conclusively demonstrate that the majority of gastroenteritis outbreaks, both food borne and institutional, were due to noroviruses.

The Norovirus is a single stranded RNA virus, classified as a calicivirus with five genogroups; I, II, and IV cause human disease.  These non-enveloped-small viruses are usually resistant to disinfection and are stable in the environment, resisting heat up to 60° C.

Epidemiology of Norovirus
The epidemiology of Norovirus is impressive in that it infects some 23 million annually in the United States, may account for 75 to 90 percent of all gastroenteritis outbreaks and is the most common cause of travelers diarrhea.  It only takes 10 virus particles to cause disease and it is now thought that Norovirus is the most common cause of viral gastroenteritis.

Transmission is usually through the fecal-oral route, but person to person and surface contact, and droplet transmission through “projectile” vomiting has also been proven. Large outbreaks have implicated oysters, raspberries and water among other things.  For example, more than 3,000 outbreak associated cases of infection over four days was traced back to and attributed to one ill employee who contaminated 76 quarts of icing distributed on various baked goods.

Characteristics of Norovirus
Norovirus, like influenza, can create new variant strains, which evade our immune system. After infection, immunity only lasts for 3-24 months and is only good for that specific strain.  If you become infected with a newer strain, you will still get sick.

Symptoms of the illness occur 10–50 hours after exposure and onset can be gradual or abrupt. Typical symptoms are usually nausea, vomiting, abdominal pain, and non-bloody diarrhea (4-8 stools per day).  Most people recover, but the very young, the very old and those with weakened immune systems are at risk of more significant outcomes including death, usually due to dehydration.

This virus has become notorious in outbreaks on cruise ships, but health care facility outbreaks have occurred as well.  One of the best described was at Johns Hopkins Medical Center in Baltimore.  The outbreak lasted from January to April 2004, infected 90 patients and 265 employees, and cost the medical center $650,000.  To control that outbreak, Johns Hopkins had to resort to more stringent infection control measures than were commonly used at the time.  Ultimately all visitors and admissions were prohibited and two units were closed (The cardiac care unit and psychiatry).

ep-34-wReducing Transmission
Prevention and control efforts should focus on the potential transmission routes.  Newer food safety laws have emphasized education regarding proper hand washing, work exclusion for ill employees, and treating vomiting incidents as emergencies requiring adequate cleaning and disinfection and disposal of anything potentially contaminated.

Aggressive control efforts in health care and long term facilities are necessary to quell epidemics.  Appropriate cleaning techniques include FDA approved disinfectants or a solution of 1:50 parts bleach/chlorine to water.  There is debate as to whether hand sanitizers are adequate for Norovirus.  Outbreaks have been stemmed with their use, but recommendations include using large amounts and rubbing hands for a minimum of 30 seconds and to use sanitizers with higher concentrations of alcohol if available.

In the past year, nationally, on a state level and locally in Brevard County, Florida we have seen increased Norovirus activity, particularly among long term care facilities, cruise ships, and in food borne outbreaks. It takes aggressive due diligence to address a Norovirus outbreak, requiring strict collaboration by everyone involved.  Patients/residents, employees, family/visitors, travelers, students, healthcare providers, etc. must work closely together to resolve this problem by vigilantly trying to minimize or prevent transmission through meticulous hand hygiene and appropriate cleaning and disinfection.

Report Norovirus Outbreak
Florida Statute, Section 381.0031 requires that any disease outbreak be reported to the Brevard County Health Department Epidemiology Section at 321-454-7101, or Ultimately recommendations for controlling an active outbreak and preventing further transmission within a facility depend on accurate information regarding the type of outbreak (food related), the extent of exposure and the number of affected persons.  After notification of an outbreak, our epidemiologists with due diligence and cooperation from everyone can help improve the situation usually within 7 to 10 days and eliminate the virus from the facility.


Barry Inman has 33 years experience in Community Health, Epidemiology, Infection Control, Health Education, Counseling and Disease Surveillance. A 1974 graduate of the University of Florida with extensive postgraduate training at the Florida Department of Health and the Centers for Disease Control in Atlanta, he has served the past 16 years as an Epidemiologist for the Brevard County Health Department in Florida focusing on control and prevention of communicable disease on the Space Coast.

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