Many of 146 people sickened with norovirus in Wheeling, IL, may have been exposed at Bob Chinn’s Crab House, the Cook County Health Department said Friday.

Bob Chinn’s, which bills itself as the nation’s fourth busiest restaurant, closed its doors Tuesday morning, after receiving complaints from customers who said they’d become sick, and then reopened Wednesday afternoon.

“We worked with the [Cook County Department of] Public Health to clean and sanitize the restaurant,” said Dan Erdman, a restaurant spokesman, told the local ABC News affiliate. “We’ve satisfied all of the requirements, and they’ve allowed us to reopen.”

Amy Poore, health department spokeswoman, said her agency received dozens of calls from people who said they became sick after eating at the restaurant, but that it’s unclear whether the eatery is the source of illness in all of those cases. Gastrointestinal illness is common this time of year.

Noroviruses, which cause more than half of all foodborne illness outbreaks, are transmitted primarily through the fecal-oral route, and fewer than 100 norovirus particles are said to be needed to cause infection. Transmission occurs either person-to-person or through contamination of food or water. Foodborne norovirus transmission can occur when food is contaminated by an infected food handler.

According to Centers for Disease Control and Prevention estimates, more than 5,400,000 people become ill from norovirus infections each year, making noroviruses the leading cause of gastroenteritis in the United States. Almost 15,000 of these people are hospitalized, primarily due to dehydration, and 149 die.