LOS ANGELES (CBS / AP) — University of Southern California officials say students have been sickened by the gastrointestinal illness norovirus in a number of campus residence halls.

City News Service reports that fewer than 100 students have come down with norovirus in the seven-day period since the illness was first reported.

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Campus health officials sent an advisory to students on Oct. 27 reporting an increased number of cases among students living in residence calls. An update sent Monday said the university increased sanitation efforts and have seen a decrease in the illness.

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Norovirus is transmitted from contaminated food or water or an infected person. Symptoms include nausea, vomiting, diarrhea, cramps, fever, muscle aches and fatigue. The symptoms generally subside within 48 hours.

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