The Department of Health and Human Services is investigating what caused more than 50 students from Salem, N.H., to become sick.

Officials at Woodbury Middle School say 54 students called in sick on Monday, and all were experiencing similar symptoms such as vomiting, diarrhea and high fever. They were about more than 100 seventh-graders who went on a four-day trip to Stone Environmental Camp in Madison last week, but school officials say no clear link has been established between the camp and the sick students.

Officials told WMUR-TV that 11 students came home early from the camp after becoming sick Wednesday night, and several more started feeling sick later.

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Information from: WMUR-TV, http://wmur.com