Massachusetts General Hospital violated Boston regulations last week when it waited four days to report a gastrointestinal infection that had stricken nine patients and 18 staff members on one floor of the building.

According to The Boston Globe, Mass. General—a Harvard Medical School affiliate—had known about the outbreak since Feb. 15, immediately prompting administrators to stop sending new patients into the ward.

But hospital officials did not notify the Boston Public Health Commission until Feb. 18, breaking a city regulation that requires institutions to alert authorities of potential outbreaks within 24 hours of discovery.

Commission spokeswoman Ann Scales said that early notification is important to prevent the disease from mushrooming.

“We were not very happy to find out four days later.” Scales said, adding that the delay was out of character for Mass. General.

She said that the commission wants to ensure that Mass. General has all the information it needs to address such problems properly in the future.

“The idea is not to be punitive, but to call them out on it,” she said.

Anita Barry, the Commission’s director of the Bureau of Infectious Disease, told the Globe that her agency would engage with the hospital to discuss prevention of similar episodes.

“If we don’t hear about these smaller groups first, how can you start to identify if there’s a larger issue?” she said in a interview with the Globe, citing concerns that hospital staff carry the disease to more than one healthcare institution.

Neither Barry nor representatives from Mass. General could be reached for further comment yesterday.

Gastrointestenal disease, or GI, is an infection that causes nausea, vomitting, and diarrhea, and lasts 24 to 48 hours.

—Staff writer Sean R. Ouellette can be reached at souellet@fas.harvard.edu.