(CNN) -- Vacationers at Yellowstone and Grand Teton national parks this summer should make extra efforts to wash their hands, the National Park Service urged Wednesday, after noting a spike in sicknesses among visitors so far.
In a news release, the park service noted "greater than normal reports of gastrointestinal illness" among those visiting the park in northwestern Wyoming as well as areas in Montana outside the two parks.
That includes an incident June 7, when members of a tour group visiting Mammoth Hot Springs -- a part of Yellowstone that's located on the Montana/Wyoming border -- began complaining of stomach and other issues. Park employees who had been in contact with this group reported similar symptoms within 48 hours.
Subsequent tests indicated that they were suffering from norovirus, which the Centers for Disease Control and Prevention notes is "a very contagious virus that (can be contracted) from an infected person, contaminated food or water or by touching contaminated surfaces."
In addition to visitors, there have been more than 100 suspected cases of norovirus among Yellowstone employees and another 50 suspected cases among Grand Teton workers, the National Park Service said in a press release.
The park service and businesses servicing visitors are taking special steps given the surge in illness, including more frequent cleaning and disinfection of public areas. As part of these measures, park employees showing signs of infection must be symptom-free for 72 hours before returning to work.
News of the spate of norovirus cases spurred a wide range of comments on Yellowstone's Facebook page, including some offering appreciation for the update and others expressing concern to hear of the illness before their planned trip to the park.
One woman said she was among the visitors who got sick around June 7, calling it "the worst pain I have ever had."
"I'm going this weekend and will be washing my hands like crazy, not to mention using disinfecting wipes after leaving public areas," another woman wrote. "This sounds like a quick way to ruin a trip hope everyone is ok!"
This isn't the first time that illnesses have plagued national parks out west.
Last summer, at least eight visitors to Yosemite National Park contracted hantavirus pulmonary syndrome. Three of them died.
Officials at that park, which receives about 4 million visitors a year, reached out to all people who stayed between mid-June and the end of August at the "signature tent cabins" that quickly became the epicenter of the investigation.
Rare but serious, hantavirus pulmonary syndrome has symptoms that mimic a cold or the flu and can be spread through contact with the urine, droppings or saliva of infected rodents, primarily deer mice.
This year, national parks are saddled with another problem: $113 million in budget cuts tied to the federal government "sequester." But there's been no indication lower funding will have any impact on how officials from Yosemite and Grand Teton parks tackle the rise in norovirus cases.