Officials are looking to roughly 170 reports of gastrointestinal illnesses, two of which have already been confirmed to be norovirus -- a highly contagious virus that causes vomiting and diarrhea -- officials announced Thursday.
The National Park Service began investigating after visitors and employees started reporting illnesses around the first week of the new year. However, since that time there has been a "significant decline" of new cases being reported, officials said.
“We’ve had very few [reported illnesses] the last week or so,” park spokesman Scott Gediman said. “We’re hoping that we’re over the hump.”
Norovirus can be spread through direct contact with an infected person, touching a contaminated surface or eating or drinking contaminated food. It can cause vomiting and diarrhea and its symptoms are especially severe for elderly people, young children and people with health issues, according to the Centers for Disease Control and Prevention.
Most of those who reported becoming sick at the national park spent time in Yosemite Valley, where park offices, visitor services, snack shops, hotels and restaurants are clustered.
However, the origin of the outbreak remains unclear and park officials have yet to determine whether people who became ill contracted something inside or outside of the park.
Park officials and medical professionals with the National Park Service Office of Public Health are working with the affected individuals as they continue to investigate the circumstances surrounding the illnesses.
So far, the majority of the cases reported have been consistent with norovirus, although some might have had food poisoning or the flu, Gediman said.
The park hasn’t tested food or facilities in the park for traces of norovirus, but Gediman said the park and its concession operators have been working to clean and disinfect public buildings to prevent future illnesses, including the famous Ahwahnee Hotel.
Aramark, which operates the hotel, received numerous complaints from visitors about poor food quality, shuttle and other services since it began managing Yosemite’s concessions four years ago.
“We share the National Park Service’s confidence that all parties are taking the necessary steps to address the situation," a spokesperson for Aramark told FOX Business.
The company is working with the park to prevent future illnesses, Gediman said.
The Associated Press contributed to this report.