Norovirus Etiology, Epidemiology, and Prevention Norovirus Acute

Norovirus Etiology, Epidemiology, And Prevention

Norovirus

Acute gastroenteritis (diarrhea) can be caused by viruses, bacteria, and parasites, but in the United States the most common cause is the norovirus (CDC, 2012b). The norovirus contributes to 800 deaths and 70,000 hospitalizations in the U.S. each year, but unless a person is elderly, very young, severely ill, or immunocompromised, most people suffer only minor symptoms. Since the estimated U.S. health care burden of norovirus infections around $2 billion annually (CDC, 2012a), this report will examine what is known about norovirus etiology and how these infections can be prevented.

Norovirus Etiology, Epidemiology, and Prevention

The norovirus belongs to the virus family Caliciviridae and contains a single-stranded RNA genome encased within an envelope-free protein isocahedral capsid (Morillo and Timenetsky, 2011). Based on recent sequencing information, noroviruses can be grouped into five genogroups: G1, GII, GIII, GIV, and GV. Only GI, GII, and GIII infect human hosts, and only the first two seem to cause disease.

Infections typically occur via the oral route and only about 20-1000 viral particles are required to cause an infection in 50% of those exposed (Morillo and Timenetsky, 2011). The incidence of infections is also enhanced by the number of viral particle produced by an infection, between 108 and 1010 per gram of fecal matter. Once infected, the typical symptoms in a healthy individual are diarrhea, vomiting, nausea, and stomach pain (CDC, 2012b). Other symptoms include fever, headache, and body aches. Since antibiotics are useless for viral infections, treatment of norovirus infections is limited to replacing lost fluids and maintaining the electrolyte balance. Antiemetics should only be used to treat adults.

After examining the data from 902 outbreaks worldwide, Matthews and colleagues (2012) found that food contamination was responsible for 54% of all norovirus outbreaks. Person-to-person, waterborne, and environmental accounted for 26%, 11%, and 9% of outbreaks, respectively. In terms of location, foodservice, healthcare, leisure, schools/daycare accounted for 35%, 27%, 17%, and 10% of norovirus outbreaks. Climate was also a contributing factor with 90% of outbreaks occurring in the northern hemisphere and 45% during the winter months. In terms of genogroups, GII was responsible for 66%, 87%, 37%, and 89% of foodborne, person-to-person, waterbourne, and environmental caused outbreaks, respectively. GI or GI+GII were equally responsible for the balance of waterborne outbreaks. GII is therefore the primary cause of norovirus infections.

The sources of norovirus infections are believed to be the contaminated employees, especially those that may have come into contact with fecal matter or vomitus (Lopman et al., 2012). Contaminated surfaces are also believed to be a significant source, since the virus can remain viable for hours or days on a dry surface and the efficacy of chemical disinfection is uncertain. Despite these unknowns, hand washing and bleach treatment of surfaces are recommended. While water sources contaminated with sewage could be a cause of disease, this link has not been established conclusively. A viable vaccine has not been developed yet and acquired immunity seems to last for only a short while following an infection; however, Morillo and Timenetsky (2012) argue that given the unknowns surrounding chemical disinfection a vaccine may be the best approach for preventing norovirus infections.