Cruise Ship Goes Viral
Cruise ship carrying over 600 passengers sickened by a gastrointestinal infection returned early to Bayonne, New Jersey port.
A norovirus is the usual culprit in mass outbreaks of infection on cruise ships. What exactly is a norovirus?
Noroviruses (Calicivirus family) are small (for a virus, 27-40 nm) non-enveloped viruses with a positive, single-stranded RNA genome. (Formerly know as Norwalk or Norwalk-like virus.)
Noroviruses are the single most important cause of non-bacterial, epidemic, acute gastroenteritis (stomach virus) outbreaks in adults in the westernized world. They are also a leading cause of food-related outbreaks of gastroenteritis in the United States.
Norovirus outbreaks can occur in any enclosed environment, such as institutional settings (hospitals, prisons, military barracks, or nursing homes), college dorms, cruise ships, restaurants, schools, and daycare centers. There was also a norovirus outbreak in 2006, after Hurricane Katrina hit the US, in a crowded, temporary evacuee center in Texas.
What are the symptoms of a norovirus infection?
Norovirus infections are usually characterized by a very abrupt onset of abdominal pain, nausea, vomiting, and diarrhea – classic GI symptoms. These can last for 24-72 hours. Usually the symptoms are mild and self-limiting, but can be very incapacitating during the symptomatic phase. Normally the illness resolves without complications.
How does norovirus spread?
Norovirus spreads rapidly for several reasons. The virus has a very low infectious dose – as few as 10 viral particles are needed to cause an infection. The virus has an incubation period of 24-48 hours, meaning that symptoms can develop one to two days after the virus particles enter the body.
There are several modes of viral transmission. The primary one is the fecal - oral route: people ingesting contaminated food or water and shedding the virus in stool, but person-to-person contact or aerosolization of contaminated body fluids can also cause an infection.
The virus is also relatively stabile in the environment and can live on objects (tables, doorknobs, desks, etc.) for hours, so infection can occur if a person comes in contact with a contaminated surface.
Can a norovirus infection kill you?
Not normally in a previously healthy person. Since the disease has such a rapid and forceful onset, dehydration is the most common complication in otherwise healthy individuals.
Some patients are at risk for more serious complications or even death. These are very young children, elderly, and immunosuppressed patients. All of these groups already have compromised immune systems and could have a more severe disease course. In developing countries, without adequate medical facilities, there are about 200,000 deaths per year in children younger than 5 years old, mostly from dehydration.
How is it treated?
Usually the infection is self-limiting. That means that it will usually go away by itself. No antiviral treatment or vaccine is available. Treatment is mainly symptomatic. Fluid and electrolyte replacement therapy is usually sufficient. Pepto-Bismol® and Kaopectate® reduce the severity and duration of abdominal cramps and may shorten the gastrointestinal symptoms.
Who is most at risk during an outbreak of norovirus?
All age groups are at risk. Living, even for a few days, in a crowded venue will maximize the spread of the virus, since it has only a one to two day incubation period.
Although a norovirus infection usually resolves by itself without complications in normally healthy individuals, it can be sufficiently severe to require medical intervention with an increased risk for life threatening dehydration at both ends of age spectrum (the elderly and infants). Immunocompromised patients (including those receiving either a transplant or chemotherapy) are at an increased risk for more severe illness, as well.
What actually happens biologically when one is infected with a norovirus?
The virus enters via an oral or aerosol route and is acid stabile (can survive passage through stomach). After a 24-48 hour incubation period, when the virus replicates in the upper intestinal tract, the patient then comes down with the acute gastrointestinal illness, lasting about 24-60 hours. It is thought that when the virus replicates in the intestines it damages the hair-like projections, called villi, lining the GI tract. These villi are responsible for the absorption of food and liquids into the body. This leads to malabsorption and abnormal gastric motor function, which are responsible for the nausea, diarrhea, and vomiting. Live virus can be shed in stool for weeks after the acute symptoms are gone.
Once an outbreak occurs during a cruise, what can individual passengers do to avoid getting sick themselves?
Outbreak management should focus on prevention of the spread of the virus. Frequent hand washing with soap is a must! This virus is resistant to ethanol-based cleaners. Alcohol-based hand sanitizers may actually increase risk of norovirus transmission! Environmental decontamination (the wiping down of ALL surfaces) requires chemical disinfection such as hypochlorite, hydrogen peroxide, or phenolic based cleaners.
Care must be taken to prevent contamination of food and water supplies. Kitchen workers must be trained in the hygienic processing of food.
Lee Ann Schein, Ph.D is an Assistant Professor, Department of Pharmacology at Robert Wood Johnson Medical School. She is the Course Director for two first year medical school courses, Microbiology and Immunology, in the Mechanisms of Disease and Defense Block. She is also the Course Director of the Microbiology and Immunology Course in the Master in Biomedical Sciences Program (RWJMS). Contact: Lee Ann Schein, Ph.D firstname.lastname@example.org