HOLLAND, MI (WHTC) - The Ottawa County Health Department is investigating an outbreak of at least 50 illnesses among people who ate at Margarita's Mexican Restaurant on 17^th Street in Holland. The first cases were reported on Thursday,and most of those who became ill recovered quickly, although one person was admitted to Holland Hospital for treatment of dehydration. Health Department spokeswoman Shannon Felgner said that, after the illnesses were reported, the restaurant voluntarily closed its doors until further notice, as well as pulling out of a booth at the Ottawa County Fair, so that the department could investigate the matter and the restaurant would conduct a thorough cleaning. A cause for the outbreak hasn't been determined yet, as health department officials are awaiting test results sent to both Holland Hospital and the state lab in Lansing, and no timetable as to when the restaurant would be allowed to reopen has been made.