Norwalk-Like Virus: 

AKA Winter Vomiting Disease 

Most adults have experienced at least one episode of viral gastroenteritis in their lives. These episodes can be caused by Rotavirus, Norwalk like virus, Adenovirus 40 and 41, Sapovirus and Astrovirus. The subject of this column is the Norwalk-like virus. It has been in the popular press and one in which Montgomery County, Maryland issued a recent alert to control an outbreak. Norwalk-like viruses causes a non-bloody diarrhea and > 50%vomiting with cramping and /or a low-grade fever. Some studies show children have more vomiting than adults and adults have more diarrhea than vomiting.  

Norwalk-like viruses are a group of single strand RNA Calciviridae. Noro virus geno type II NoV were responsible for 270 U.S. outbreaks from 2000 -2004, mostly in nursing homes, retirement facilities and hospitals. The Centers for Disease Control (CDC) reports more than half of the Norwalk-like outbreaks were food borne associated. Cruise ship outbreaks are common. In one study there was a positive association for cases with an ill roommate or using a toilet after a person had vomited. There have been reports in hotels in Virginia 2000 and workplace canteens (cafeterias) in Finland 2006.   

The problem with containment and control efforts rests with the virulence and the persistence of the virus. The Norwalk like viruses are a medium sized -virus 35 nm, but require as few as 10 -100 to cause illness, versus hundreds for Salmonella to cause illness. Once exposed, the incubation is12 -24 hours with duration of symptoms as long as 60 hours.  Three out of 10 persons will be asymptomatic.  Anectdotally, in one outbreak, nausea alone was noted.

Viral shedding is important to note and can persist at least seven days after symptoms have ceased. 

Transmission of the virus is from person to person, through fecal oral route, contact, and airborne vomitus. The airborne capacity of the virus and the ability of the virus to persist, despite freezing and heating to 140 degrees Fahrenheit contribute to outbreaks.  Hand transfer of the virus to oral mucosal, materials, fomites, and environmental surfaces are important modes of transmission. In one study using a surrogate marker for Noro virus, feline calcivirus, the virus persisted for 8-48 hours on keyboards. 

Control measures at this time are diligent hand hygiene with plain soap and environmental sanitation with bleach solution of one cup with 50 cups of water, made at the time of use. Lysol or other household or commercial phenolics require 2-4 times the normal recommended concentration for use, so are not generally used. CDC recommends commercial laundering in facilities and replacing air filters. Gloves and masks should be worn when cleaning up vomitus from surfaces. From personal experience in 2004, as an occupational health nurse I cleaned up some linens from a hotel guest visiting from   Pennsylvania, with Norwalk- like illness and within 24 hours I had the same vomiting. Gloves were worn, but not a mask.  

In two other outbreaks during the last 20 years, one in a DC Hospital and a VA Nursing home I was attempting to control the outbreaks that lasted for weeks but I remained asymptomatic because I had learned through the challenges of controlling these viruses.  

While less than 80 deaths were reported annually in Great Britain in a five-year period 2001-2006, 20% of the deaths were over 65 years old. In general, deaths are rare but are due to severe dehydration from vomiting and diarrhea. Electrolyte replacement is critical in all age groups. 

Immunity is short lived from studies of IGG in persons during outbreaks. Antibodies rise five days after onset of illness, peak at week three and fall by week six. So recurrence of symptoms can occur. Persons with blood type O seem to have the greatest risk for severe infection.  

Work loss data were not found at the time of this writing. Food handlers should not report for duty until 24 hours after recovery from diarrhea per FDA regulation. CDC recommends 72 hours after cessation of diarrhea. This is conservative given the capacity to shed the virus for seven days after onset of illness. Paid sick leave is an incentive to control spread of these and other infections.  

CDC does not conduct active surveillance on Norwalk-like viruses, but does monitor Food Net outbreaks and those outbreaks reported by the state and territorial epidemiologists. Laboratory testing for these viruses and others are in continuous development. Molecular sequencing will further define the public health impact of Norwalk-like viruses. Laboratory and epidemiologic studies will further assist in control measures. In the meantime, the Norwalk-like virus, formerly known as Winter Vomiting Disease is here to stay worldwide, year round.