PORTLAND, Ore. (AP) — An Oregon epidemiologist says about 90 of the 220 medical professionals who attended a private meeting at the Oregon Zoo became ill.

Oregon Public Health's Dr. Katrina Hedberg says no one was hospitalized but those who developed gastro-intestinal symptoms were very ill.

She tells The Oregonian (http://is.gd/LVGk9K ) that the highly contagious norovirus is "the most likely culprit."

Oregon Public Health scientists are trying to determine the source of the contamination at the Dec. 5 meeting of Women's Healthcare Associates. Hedberg says it's most likely that an infected food handler contaminated the food. Zoo staff catered the event, which was held in a space that the zoo rents out to private parties.

Women's Healthcare Associates is a group of physicians, midwives and nurse practitioners serving the Portland area and Newberg. CEO Brian Kelly says the group is working with officials to determine the cause of the illness.

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Information from: The Oregonian, http://www.oregonlive.com