'Tis the Season for Norovirus

Indiana Epidemiology Newsletter
December 2007

Jennifer Wyatt, MPH
ISDH Field Epidemiologist, District 4

Steven Allen
ISDH Field Epidemiologist, District 9

Communities beware: norovirus season has arrived! Noroviruses are the most common cause of viral gastroenteritis. Outbreaks commonly occur in schools, hospitals, long-term care facilities, day-care centers, jails, food establishments, or anywhere else people congregate in a community setting. Although norovirus infection can occur any time of year, peak activity most often occurs roughly from November-February, overlapping influenza/respiratory seasonality.

In 2006, a new strain of norovirus emerged, resulting in a surge of outbreaks in many Indiana counties. Over 100 long-term care facilities reported an excess number of patients ill with signs and symptoms of viral gastroenteritis. Of the 100 outbreaks investigated, 28 were confirmed as norovirus by laboratory testing and 72 were suspected. A suspected outbreak is defined as one in which individuals experience symptoms consistent with norovirus infection but are not laboratory confirmed.

In October 2006, the ISDH Surveillance and Investigation Section developed a database to track norovirus outbreaks in anticipation of outbreaks occurring this season. It is important to report a suspected norovirus outbreak as soon as possible since the virus can move quite rapidly throughout a facility or population. Many of the suspected outbreaks that have been reported in Indiana have been reported after the outbreak has ended. Reporting a suspected outbreak as early as possible can help ensure rapid control, containment, and prevention of further illnesses.

Noroviruses are transmitted by the fecal-oral route, usually through contaminated food or water, contact with contaminated objects, and close contact with those infected. Only a small amount of virus is needed to cause infection. Symptoms of norovirus typically include diarrhea, vomiting, nausea, and stomach cramping, which usually occur 12-48 hours after exposure. Chills, headache, low-grade fever, and muscle aches can also occur in some people. Norovirus infection is usually a self-limiting illness with symptoms typically lasting one to two days. Because infection is viral, antibiotics are not effective in treating the infection. Currently, there is no vaccine or antiviral treatment that can be used to fight norovirus infection. There are many different strains of norovirus; therefore, a person can have recurring infections.

In general, most viral gastroenteritis can be prevented by strictly adhering to the following guidelines:

  1. Thoroughly wash hands with soap and water:
  2. Before preparing and serving food
  3. After using the restroom
  4. After eating
  5. After diapering a child
  6. After cleaning a soiled area
  • Persons with diarrhea and/or vomiting should not prepare food for others and should limit direct contact with others as much as possible;
  • Staff with diarrhea and/or vomiting shall be excluded from employment involving food handling (Indiana Retail Food Establishment Sanitation Requirements, 410 IAC 7-24-122); and
  • Wash all produce before eating raw or cooking.