Also known as: Norwalk-like virus, viral gastroenteritis
Hospital: Report all potential outbreaks, send stool specimens with specific request for norovirus testing. State Hygienic Laboratory (SHL) is the only laboratory in the state that can test for Noroviruses.
Lab: Report all potential outbreaks; send stool specimens with specific request for norovirus testing. The University of Iowa State Hygienic Laboratory (SHL) is the only laboratory in the state that can test for Noroviruses.
Physicians: Report all potential outbreaks
Local Public Health Agency (LPHA): Report all potential outbreaks of norovirus, send stool specimens with specific request for norovirus testing. State Hygienic Laboratory (SHL) is the only laboratory in the state that can test for Noroviruses.
Iowa Department of Public Health
Disease Reporting Hotline: (800) 362-2736
Secure Fax: (515) 281-5698
Noroviruses (genus Norovirus, family Caliciviridae) are a group of related, single-strand RNA, nonenveloped viruses that cause acute gastroenteritis in humans. Norovirus is the official genus name for the group of viruses formerly described as “Norwalk-like viruses” (NLV), or “small round viruses.”
B. Clinical Description
Symptoms: The symptoms of norovirus illness usually include nausea, vomiting, diarrhea, and some stomach cramping. Sometimes people have a low-grade fever, chills, headache, muscle aches, and a general sense of fatigue. The illness often begins suddenly, and the infected person may feel very sick. The illness is usually brief, with symptoms lasting only about 1 - 2 days.
Onset: Symptoms of norovirus illness usually begin about 24 - 48 hours after ingestion of the virus, but they can appear as early as 12 hours after exposure.
Complications: Dehydration may result in persons with norovirus disease, which may require hospitalization. There are no known long-term effects.
Humans are the only known reservoir.
D. Modes of Transmission
Noroviruses are very contagious and spread easily from person to person. It is believed that an inoculum of as few as 10 viral particles may be sufficient to infect another individual.
Norovirus may be transmitted in a variety of ways:
most commonly through the fecal-oral route, either by consumption of fecally contaminated food or water or by direct person-to-person spread
by environmental and fomite contamination acting as a source of infection
by transmission due to aerosolization of vomitus that presumably results in droplets contaminating surfaces or entering the oral mucosa and being swallowed.
E. Incubation period
The symptoms of norovirus appear about 24 - 48 hours after ingestion of the virus, but can appear as early as 12 hours after exposure.
F. Period of Communicability or Infectious Period
People infected with norovirus can be contagious from the moment they begin feeling ill, until several days after symptoms end. The virus can be shed for two weeks or more after recovery, although it is unclear whether virus shedding during this time is infectious. Infected people do not become longterm carriers of norovirus.
Norovirus is common worldwide, and is mostly associated with sporadic outbreaks. All age groups are affected. Norovirus is the most common cause of acute gastroenteritis in the United States. Each year, it causes 19-21 million illnesses and contributes to 56,000-71,000 hospitalizations and 570-800 deaths. Norovirus is also the most common cause of foodborne-disease outbreaks in the United States.
In Iowa, noroviruses cause the majority of foodborne illness outbreaks. Rough, wet, uncooked foods are at highest risk of transmission. Most foodborne outbreaks of norovirus illness arise from direct contamination of food by those who handle the food before it is eaten. Outbreaks have frequently been associated with consumption of cold foods, including salads, sandwiches, and bakery products.
Most outbreaks are due to person-to-person spread, but many are foodborne. Implicating a specific food in foodborne norovirus outbreaks is often difficult. Rough, wet, uncooked foods such as salads, sandwiches, and bakery products pose the highest risk of transmission. Most foodborne outbreaks of norovirus arise from direct contamination by those who handle the food before it is eaten.
There have also been outbreaks associated with people vomiting and aerosolizing virus in public settings. Waterborne outbreaks of norovirus have been caused by sewage contamination of wells and recreational water. Diapered children playing in “kiddie” pools filled with tap water (pools that have not been chlorinated) have also been associated with norovirus outbreaks.
H. Bioterrorism Potential
I. Additional Information
Note: Refer to Iowa’s Foodborne Illness Outbreak Investigation Manual available at www.idph.state.ia.us/idph_universalhelp/main.aspx?system=IdphFoodborneDiseaseManual
CDC website providing the most up-to-date norovirus information: www.cdc.gov/ncidod/diseases/submenus/sub_norwalk.htm
CDC website providing the most up-to-date norovirus information: www.cdc.gov/ncidod/dvrd/revb/gastro/norovirus.htm
Heymann, D.L., ed. Control of Communicable Diseases Manual, 20th Edition. Washington, DC, American Public Health Association, 2015.