Epidemiology and Management of Noroviruses in Healthcare Facilities

David J. Weber

by David J. Weber, MD, MPH

Acute gastroenteritis is one the most common illnesses, affecting both adults and children.  Infection is the most common cause of acute gastroenteritis.  Pathogens include viruses (e.g., norovirus, rotavirus), bacteria (Campylobacteria, Salmonella, Shigella, E. coli, Clostridium difficile), and protozoans (e.g., Giardia, ameba).  Among viruses the most causes of infection are human caliciviruses (including noroviruses and sapoviruses), enteric adenoviruses, rotaviruses, and astroviruses.  However, the caliciviruses, principally noroviruses, are the most common cause of acute gastroenteritis in both adults and older children with an estimated 23 million illnesses in the United States each year. 

Noroviruses contain a single-strained RNA genome.  As with other RNA viruses there is substantial genetic diversity among these viruses.  Noroviruses are subdivided into five genotypes based on sequence homology.  Genogroups GI, GII and GIV include human pathogens and multiple genotypes are recognized within each group. 

Noroviruses cause an average of 20 million total illnesses, 1.8 million physician visits, 400,000 ED visits, ~60,000 hospitalizations, and ~700 deaths per year.  Young children (i.e., <5 years of age) and older adults (>65 years of age) are at greatest risk for hospitalization and death.  Although illness occurs throughout the year, there is a pronounced winter peak (hence the name “winter vomiting disease”).

Novoviruses are readily transmitted person-to-person (via the fecal oral route) and spread through airborne droplets, food, water, fomites, and contaminated surfaces.  As few as 18 viruses are infectious and viral shedding can occur at levels as high as ~8.0x10¹⁰ viruses/gm of stool.  Although the major route of transmission is fecal-oral, there are also observations from outbreaks that suggest that on occasion airborne transmission can occur, most likely when virus is aerosolized during vigorous emesis.  Immunity to norovirus is relatively short lived and persons can become repeatedly infected. 

The incubation period for norovirus is generally 24 to 48 hours (range, 18-72 hours) and the onset is typically abrupt.  Most patients have both vomiting and diarrhea although either can be present alone.  Fever accompanies the GI symptoms in about 50% of cases.  Diagnosis is usually based on clinical signs and absence of bacterial pathogens in the stool, although specific tests on stool are available to detect noroviruses. 

Outbreaks in healthcare facilities are characterized by high attack rates among patients, hospital personnel, and visitors.  Large outbreaks in hospitals most commonly occur in wards in which patients move room-to-room and eat together such as psychiatry units and rehabilitation units.  Outbreaks in extended care facilities are common.  A norovirus outbreak should be suspected when several epidemiologically linked patients develop vomiting and/or diarrhea with an average incubation period of 24-48 hours, the average duration of illness is 12-60 hours, vomiting is reported in more than 50% of cases, and patients have negative stool cultures for bacterial pathogens.

Norovirus outbreaks are the most common cause for ward closure.  Because of the explosive nature of these outbreaks and short incubation period, there are NO proven methods to curtail the outbreak.  Rather the focus is on limiting the impact of the outbreak and trying to contain the outbreak to a single ward.  The following steps should be taken if a patient has known or suspected norovirus infection:

• Immediately initiate contact precautions (i.e., gloves and gowns for entering the room for all healthcare personnel and visitors).  The patient should be placed in a single room.
• Hand hygiene with soap and water, or water and an antiseptic.  Avoid the use of alcohol-based antiseptics.
• Clean the environment daily with an EPA-registered disinfectant with a claim against norovirus.  The most commonly used agent is 5,000 ppm hypochlorite (i.e., diluted bleach).
• Remove vomitus and fecal material carefully to limit aerosolization (i.e., soaking up material with disposable cloths or towels with minimal agitation with disposal in impervious bags)

In outbreak situations (i.e., >3 healthcare personnel and/or patients ill)

• Prohibit any group eating on the ward (also no eating by healthcare personnel on the ward).
• Place on sick leave all healthcare personnel with vomiting and/or diarrhea.
• Consider closing the ward to new admissions until the outbreak has ceased.
• Prohibit patient transfers from the ward to other wards until the outbreak has ceased. 
• To the extent possible, minimize staff from caring for patients on the affected ward and patients on other wards (such as physical therapy, occupational therapy, respiratory therapy, and nursing). 
• Increase room disinfection to twice daily.