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Outbreak of norovirus reported in two national parks
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The National Park Service recently issued an alert about norovirus to visitors to Yellowstone and Grand Teton national parks after more than 150 employees and visitors reported gastrointestinal illness.
As of June 19, more than 100 suspected cases of norovirus have been reported among employees in Yellowstone and approximately 50 suspected cases among employees in Grand Teton. Fifty visitors also were treated for symptoms of gastrointestinal illness within Yellowstone.
According to the alert issued by the park service, the outbreak began when several members of a tour group arrived in Mammoth Hot Springs, Wyo., on June 7 and complained of gastrointestinal symptoms. Within 48 hours, numerous park service employees reported similar symptoms. Laboratory results from samples taken from visitors and employees were positive for norovirus.
The National Park Service and surrounding businesses that serve park visitors have instituted a variety of infection precautions to limit the spread of the virus. These include increased cleaning and disinfection of all public areas, including stores, gift shops, restaurants and lodging facilities, and isolation of potentially infected employees until they have been symptom-free for at least 72 hours.
Perspective
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Andi L. Shane, MD, MPH, MSc
Noroviruses have been characterized as belonging to one of five genogroups (GI through GV), which are subdivided into 34 genotypes; GI and GII noroviruses, cause disease in humans and GII.4 strains are most commonly associated with cruise ship and health care facility outbreaks.
In March 2012, GII.4 Sydney emerged in Australia and was responsible for clusters of infections and outbreaks locally and in several European countries and the United States. Although norovirus outbreaks are more common during the winter months, this seasonal predominance may not be seen when an emerging strain circulates. While molecular identification of the strain associated with the national parks is ongoing, it is possible that GII.4 Sydney or another emerging strain will be implicated.
One hundred norovirus virions are probably all that are needed to transmit infection via person-to-person contact. Transmission has been associated with the aerosolization of norovirus-contaminated vomitus. An outbreak of norovirus is defined as an occurrence of two or more illnesses associated with a common exposure. A very low infectious dose makes transmission very efficient, especially in environments where there are many individuals in small spaces.
Cruise ships, hospitals, long-term care and child-care facilities are ideal for propagation of infections. Norovirus has been implicated as the etiological agent in 50% of foodborne outbreaks in the United States, with a predilection for uncooked food products, vegetables, fruit and shellfish.
Norovirus transmission has been associated with contaminated utensils used in the preparation of food and tableware used in the consumption of food. A campsite or national park may be a source of crowding, suboptimal food preparation and serving practices by campers and visitors, and opportunities for insufficient hand hygiene, providing opportunities for norovirus outbreaks.
Rapid diagnostics for norovirus have 50% sensitivity and are therefore not recommended for diagnosis of the individual. Reverse transcriptase-quantitative PCR (RT-qPCR) assays are available in research and health department laboratories, and may detect norovirus in stool, vomitus, food and water. There is currently no licensed vaccine for norovirus, although there are candidate vaccines being assessed in clinical trials.
Hand hygiene and careful food preparation practices are the most effective preventive measures. Health care providers should report all clusters of patients with acute gastroeneteritis to state, local or territorial health departments so that intervention may occur if necessary. The National Outbreak Reporting System (NORS) and CalciNet seek to capture all suspected and confirmed norovirus associated outbreaks.
National parks have not issued restrictions on facility use; however visitors have been advised to optimize hand hygiene and to utilize alcohol-based hand sanitizing products when soap and water are unavailable. Anyone participating in food preparation activities should optimize hygiene and ill individuals should refrain from food preparation activities.
Summer activities may be continued to be enjoyed with special attention to hygiene.
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