Norovirus

The most common cause of gastroenteritis in the U.S. among patients of all age groups.

A highly contagious, stomach bug characterized by sudden vomiting and diarrhea.

It can arise through cruise trips, long-term care, facilities, and school cafeterias.

Norovirus virus is the leading cause of acute gastroenteritis worldwide.

In the US, it causes more than 50% of all foodborne illnesses.

Each year accounts for a half 1 million emergency department visits, mostly for young children and roughly 900 deaths predominantly in older adults.

Norwalk agent the leading cause of epidemics of gastroenteritis and an important cause of sporadic gastroenteritis in children and adults.

Single positive-strand RNA virus, approximately 7.7 kb in size, enclosed in a non-enveloped protein coat with cuplike depressions.

Genus norovirus and family Caliciviridae.

At least 25 genotypes exist, along with numerous subgroups, but genogroup II, genotype IV is responsible for majority of cases, and outbreaks.

Have not been grown in cell culture.

The virus is known to persist on environmental surfaces for up to two weeks, and resists many commercial disinfectants.

As few as 18 virus particles are enough to cause an infection.

Susceptibility to Norwalk virus is dependent on the expression of a functional focosyl-transferase 2 (FUT2) gene, and individuals who had a nonfunctional FUT2 gene are genetically resistant to such virus infections.

Mutations are responsible for genetic drift, and the emergence of variants is responsible for epidemics.

Humans are the only known hosts.

Estimated 23 million cases per year in the U.S.

Estimated 570-800 deaths per year.

Estimated to be responsible for 56000-71000 hospitalizations and 400,000 ED visits and 1.8 million outpatient visits per year.

US resident has a lifetime risk of having a norovirus gastroenteritis in his or her lifetime.

Average incubation period is 24-48 hours.

Infection manifested by acute onset of vomiting and/or diarrhea that lasts 12-60 hours.

Symptoms pass after a few days, but threatens the health of populations, especially those suffering from malnutrition, chronic starvation or dehydration, norovirus contributes, nearly one in five episodes of diarrheal disease, worldwide.

The most vulnerable population includes children, younger than five years, older adults, and people who are immuno compromised.

In developing countries death from norovirus is common among children who make up more than 1/3 of the global death toll.

Cost $60 billion to society including $4.2 billion in healthcare cost globally every year.

The norovirus can be transmitted by touching and then ingesting it from contaminated surfaces, and it can be inhaled.

Patients who have recovered from the infection can continue to shed the virus for weeks, and it can live on surfaces for even longer.

It can cause fever and headaches.

There are nearly 50 genotypes split into 10 groups.

Type G1 and G II are the most common.

Dominant neurovirus strains change and invade immune systems.

GII caused most of the neurovirus cases in the US presently.

GIV viruses the ones that caused pandemic levels of disease and cyclic patterns overtime: they can evade immunity by changing themselves.

Immunity is variable and estimated from several months to up to nine years.

Vaccine production has been difficult, and is presently under investigation.

Approximately two thirds of people infected are symptomatic.

Generally mild and of short duration, but at times can be severe and even fatal, especially in the young and elderly.

Primary route of transmission of noroviruses is fecal-oral, with consumption of contaminated water or food, person-to-person contact, and from contaminated objects or environments.

Can be transmitted by airborne vomit droplets.

Primary cases may come from fecal contamination and secondary cases may result from person-to-person contact.

Infectious vomitus may play a role in infection transmission.

Associated with transmission with a low infectious dose of approximately 18 to 1000 viral particles to allow spread through droplets, fomites, person-to-person contact and environmental contamination (Teunis PF).

Low dose exposure can lead to infection, virus can be shed in a prolonged and asymptomatic fashion.

Secondary attack rates of 30% or more among family members and close contacts, indicates the significant infectious nature of the virus.

Viral shedding precedes the clinical onset of illness in up to 30% of exposed patients and may continue long after the illness abates, and can increase the potential risk of secondary spread among family members and food handlers.

The virus can survive in temperatures from freezing to 60°C and 10 persist on environmental surfaces, in recreation bodies of water, drinking water, and in foods such as raw oysters and fruits and vegetables exposed to sewage and uncooked.