Outbreak Sickens Yellowstone Campers Those heading on a camping trip this summer might want to be just as wary of crossing paths with the wrong bacteria as they would a hungry bear. After 200 park employees and visitors reported bouts of gastrointestinal illness at Yellowstone National Park and nearby Grand Teton National Park this month, national park officials have warned visitors to be vigilant about hygiene. The outbreak started on June 7, when a group touring the Mammoth Hot Springs complained of stomach flu and other gastrointestinal problems. After the tour group members reported their illnesses, about other 50 visitors and 150 park employees reported similar symptoms. Preliminary reports found that they had norovirus, or "stomach flu," which affects up to 21 million people, every year according to the Centers for Disease Control and Prevention. Doctors Warn of New Stomach 'Superbug' Hitting U.S. Al Mash, spokesman for Yellowstone National Park, said campers who were worried about the outbreak should take care to properly store their food and wash their hands with soap and water before eating. Don't rely on hand sanitizer. It's good for a while if you don't have access to water," said Mash. But sanitizer is a poor second to washing your hands. According to the CDC, the norovirus can be very contagious and is usually passed from contaminated surfaces or food. Mash said that while it might be more difficult to wash hands before and after meals on camping trips, sporting goods stores sell soap slivers or biodegradable soap that can be used on camping trips. "My manta is be aware but not afraid," said Mash. Employees at Yellowstone and nearby Grand Teton park have been cleaning and disinfecting the areas where the illnesses were first reported. Yellowstone National Park regularly has 20,000 visitors a day. The norovirus outbreak is just the latest one to hit the national parks. Last year, Yosemite National Park experienced an outbreak of the deadly hantavirus. Infection with hantavirus, often contracted through contact with contaminated mouse feces or urine, can lead to hantavirus pulmonary syndrome, which can be fatal, according to the CDC. For Hantavirus Survivors, Yosemite a Painful Reminder During last summer's outbreak, eight people were sickened and three died. To stop the spread of disease the National Park Service tore down the buildings where the outbreak was centered and are currently trapping and testing mice for the hantavirus. Kathy Kupper, a spokeswoman for the National Park Service, said if campers were worried about becoming sick they should be sure to check in with the park's website or information line before they arrive. Any potential hazards from disease outbreaks from high concentrations of ticks, for example, will be listed in each national park's newsletter or on its website. Always pay attention to the information. Don't just take the [informational pamphlet] and throw it in the glove box," said Kupper. Kupper said the one piece of camping safety advice, which is most often forgotten, is to stay put if lost. "Otherwise it's like a wild goose chase," said Kupper. Stop moving. That way you're conserving energy, and rescuers have a better chance to find you.