YOSEMITE NATIONAL PARK, Calif. (AP) — Yosemite National Park is investigating about 170 reports of gastrointestinal illnesses that officials say are consistent with norovirus.

Park spokesman Scott Gediman says the reports began coming in earlier this month but have decreased recently. Gediman says it’s unclear where the outbreak originated, but the park has been working with its concession owners to clean and disinfect public buildings, hotels, restaurants and other facilities, including the famous Ahwahnee Hotel.

Norovirus can cause vomiting and diarrhea and its symptoms are especially severe for elderly people, young children and people with health issues.