YOSEMITE NATIONAL PARK (CBS SF) — There have been at least two confirmed cases of norovirus among the approximately 170 visitors and staff members at Yosemite National Park who have experienced a gastrointestinal illness this month, park officials said.

The affected individuals include park visitors and employees and most have spent time in Yosemite Valley.

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Park rangers said most of the cases occurred on and around the first week of January and there had been a significant decline of new cases reported over the past several days.

Yosemite National Park officials and medical professionals with the National Park Service Office of Public Health were continuing to investigate the circumstances surrounding the outbreak and were continuing to conduct interviews with affected people.

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Health officials said the overwhelming majority of the reported cases were consistent with the symptoms of norovirus.

Norovirus spreads very easily, including through direct contact with an infected person, touching a surface or object contaminated with malady or eating food or drinking liquids contaminated with norovirus. Symptoms usually begin 12–48 hours after exposure.

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The Park also continued to undertake extensive cleaning and enhanced sanitation protocols.