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About 170 people have reported norovirus symptoms after visiting Yosemite National Park in Northern California, according to the National Park Service.

As of Thursday, park officials had confirmed two cases of norovirus, but dozens of Yosemite Park visitors and employees had reported gastrointestinal illness, according to a statement from the park. Most of the sickened people spent time in Yosemite Valley.

"The overwhelming majority of the reported cases are consistent with norovirus," the statement said.

Most of the people who got ill were sickened around the first week of January, and there has been a decline of new cases reported in the past week, according to the park.

Norovirus is highly contagious. It can spread by having contact with an infected person, consuming contaminated food or water or touching contaminated surfaces and then touching one's mouth, according to the Centers for Disease Control and Prevention. The most common symptoms are diarrhea, vomiting, nausea and stomach pain.

Yosemite officials and medical professionals with the National Park Service Office of Public Health are investigating the outbreak and interviewing those who have fallen ill.