The Baltimore Health Department said late Wednesday that investigators believe a faulty hot water heater sickened 23 people at the Johns Hopkins at Keswick complex this week.
An estimated 600 people were evacuated from the complex Tuesday afternoon after people reported difficulty breathing. Standard checks by emergency officials ruled out exposure to carbon monoxide, explosives, hydrogen sulfide and low oxygen. Investigators said they also were examining the possibility of food contamination.
Now, health officials say it was a hot water heater that allowed nitrates to seep into the water service at the complex's south building. The health department said symptoms of overexposure to nitrates include dizziness, nausea, difficulty breathing and vomiting.
"The hot water heater in question only serves the north side of the south building, where running water with those chemicals was found, and where sickened employees have reported coming into contact with water in various ways: eating food cooked with hot water, drinking beverages made with hot water, or using restrooms," the health department said in a statement.
The complex, closed Wednesday, will reopen Thursday, though some affected sinks, restrooms and other water sources will be shut down. The heater is to be replaced.
Nitrates are typically found in water as a result of fertilizer runoff, especially in wells. They are typically the cause of "blue baby syndrome," which stops the breathing of infants.
Those who fell ill were asked to cooperate with any inquiry by Dr. Trish Perl, director of epidemiology and infection prevention for the Johns Hopkins Health System. The city health department worked with the Maryland Department of Health and Mental Hygiene, Transwestern Commercial Services and Johns Hopkins to investigate the illnesses.
Not everyone who experienced symptoms Tuesday was taken to a hospital. But all 17 who were had been discharged by Wednesday, officials said.
"We send best wishes to those who became sick and sincere regrets for your discomfort," Hopkins said Wednesday in a memo to employees.
The buildings house about 1,050 administrative workers for the Johns Hopkins University and the Johns Hopkins Hospital and Health System.
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