The organism which caused food poisoning on March 26 at South House, leaving more than 20 people ill and 4 hospitalized, was identified at state laboratories yesterday as a rare bacteria found in uncooked seafood.

Dr. Warren E. Wacker, director of University Health Services, said yesterday that epidemics caused by this organism--called vibrio parahemolyticus--sometimes occur in Japan, where large quantities of raw fish are consumed, but "practically never" appear in New England.

Wacker said it took nearly three weeks to identify the organism because it is so uncommon. The state health department has recorded only one previous epidemic, of this kind caused from eating undercooked lobster, he said.

Eleven of the victims here, who had all eaten seafood newburg at Cabot and Whitman halls, reported to UHS the following day complaining of nausea, vomiting, and diarrhea.

Insufficiently Cooked

Wacker said these symptoms indicated that the seafood which contained shrimp, whitefish and scallops, had not been sufficiently cooked.

"I've been here four years now, and this is the first outbreak I've seen. "Wackersaid yesterday. He added that the last documented food poisoning epidemic here was thirteen years ago.

Frank Weissbecker, director of food services, said yesterday that the seafood newburg dish may be listed on the menu again as a meatless alternative, but that these menus are open to change.

He said that he will have to speak to Wacker about the results of the tests before he can recommend procedures to prevent similar incidents in the future.