As of Thursday afternoon, 57 people had reported their illnesses to the health department, said Medical Director Dr. Robert Schirmer.
"But that number will grow," he said, as officials continue to find and interview people who ate at the restaurant.
As many as 18 employees became sick, he added.
So far, everyone who was sickened ate there Saturday or Sunday, and health officials believe the outbreak was contained to those dates.
"We haven't found anyone who ate at the restaurant Monday who became ill," he said, adding: "We don't think there's an ongoing outbreak."
The cause of the illness is not known, although Schirmer suspects a highly contagious, Norwalk-like virus, which he said is responsible for most food-associated illnesses.
He hopes to confirm the cause by early next week.
The virus can be spread through direct contact with an infected person, eating contaminated food or touching contaminated surfaces or objects and placing that hand in one's mouth.
Health department spokeswoman Penny Pierce called the outbreak "larger than normal."
The department sees one or two outbreaks of food-related illness every year, but this one is notable, she said, "just because of the volume of people at this one location."
The restaurant is cooperating with the health department's investigation and has discarded all food prepared Saturday through Monday, said Joe Kadow, executive vice president of Outback Steakhouse Inc., which owns Carrabba's Italian Grill.
"We have and will continue to review and reinforce all of our food safety procedures with our employees," he said in a statement, "and we have tested all of our equipment to ensure all are in compliance with manufacturers' standards and those of the health department."
An employee who answered the phone Thursday said the restaurant is open for business and has been all week.
The first report of illness came at about 4:30 p.m. Monday.
The health department compiled a list of patrons that evening and began contacting people on the list Tuesday.
The virus, which can cause vomiting and diarrhea, was named for an outbreak about 30 years ago in Norwalk, Ohio.
The illness received international attention in 2002 when it sickened more than 1,000 passengers on cruise ships.
Symptoms usually appear between 12 and 48 hours.
Recovery takes from half a day to 2 1/2 days.