A norovirus outbreak has gripped Yosemite National Park, with around 170 people reporting symptoms the past couple of weeks. Two cases have been officially confirmed as norovirus, while many others, including some park employees, have claimed to be suffering from symptoms corresponding to the illness. According to park officials, the majority of those taken ill visited the park around the first week of January.

A park spokesperson has said that Yosemite is now implementing “extensive cleaning and enhanced sanitation protocols” to address the issue.

Encouragingly, there has been a decline in the number of new cases reported this past week, though the staggering volume of illnesses earlier in the month is certainly still cause for concern.

Norovirus is a highly contagious stomach illness that causes vomiting and diarrhea and spreads upon contact with other infected people, contaminated food or water, or contaminated surfaces. It affects between 19 and 21 million people each year in the US.

To safeguard against contracting norovirus, it’s simple. Just make sure to wash your hands as frequently as possible, or if soap is unavailable, use an alcohol-based hand sanitizer.