Norwalk virus and related "Norwalk-like viruses" are the most common cause of outbreaks of stomach sickness (nausea, vomiting, diarrhea) in older children and adults in the United States. These viruses are sometimes found in drinking water, ice, shellfish and in other foods. They can be spread easily from contact with water, food, objects or hands that have even small amounts of feces from someone who was sick.

The purpose of this research study is to see how long Norwalk virus can survive in water and still be able to cause sickness. When this is determined the researchers will be able to recommend risk levels for norovirus contaminated waters. Another purpose for this study is to see how a person's body's immune cells respond to Norwalk virus in the body. During this study volunteers will receive a dose of Norwalk virus in water that may make them sick.

Inclusion Criteria:

• Normal healthy volunteer
• Must be within 33% of normal body mass index

Exclusion Criteria:

• Have a job in which they handle food
• Work in a child care, elderly care center or if they live with young children or anyone who has a weak immune system
• Are not willing or able to wash their hands every time after they go to the bathroom, or before and after they prepare or handle food for up to eight days after they take the virus
• Are over the age of 50
• Are pregnant
• Have tested positive for the HIV virus