Several more people fell ill at the Johns Hopkins at Keswick campus this week, following an incident last month in which nearly two dozen employees reported dizziness, nausea and headaches.
Officials have tied the previous illnesses to a hot water heater that became contaminated with nitrites when a technician accidentally inserted the chemicals into the drinking water system instead of the heating system. Overexposure to nitrites can cause a range of symptoms that include difficulty breathing.
The boiler has been replaced and the water system flushed, officials have said.
Johns Hopkins officials did not immediately have details on three people who went to the hospital feeling sick Tuesday. Hopkins spokesman Dennis O'Shea said one person taken to the hospital Monday felt ill after eating food heated in a microwave.
"We are not yet cooking or selling food in the building, so that food could not have come from the building," O'Shea wrote in an email. One person who felt ill Tuesday has returned to work, O'Shea said.
Buildings at the Keswick campus, which hold offices for hundreds of administrative workers at Hopkins, were evacuated last month and temporarily shut down after almost two dozen reported feeling ill and were hospitalized. About a dozen people reported feeling ill about a week later and seven were hospitalized, but Hopkins officials insist the building is safe.
The city health department was not aware of the cause of the illnesses this week, a spokeswoman said.