Health officials continue to investigate how contaminated hot water sickened nearly two dozen people at the Johns Hopkins at Keswick complex Monday, but the case is similar to previous ones involving faulty water-heating systems that let chemicals mix into drinking water.
Twenty-three people at the Hopkins facility — home to about 600 health system and university administrative workers — fell ill with headaches, breathing difficulty and dizziness.
The investigation confirmed that chemicals known as nitrates and nitrites in the water supply were responsible for the illnesses, but officials still are exploring their origin. That leaves questions for the complex's workers — many of whom returned to work Thursday — and neighbors.
"It's going to take some more testing for us to say how it became a source," said Tiffany Thomas Smith, the city health department spokeswoman, of the water heater. "We have isolated it as a source."
The chemicals found in the water can cause low blood pressure and a blood disorder that makes it difficult for the body to deliver oxygen to organs and tissues, creating symptoms including shortness of breath, dizziness and, in severe cases, coma or death.
When humans are exposed to them — whether by ingesting, absorbing through the skin or breathing through the air — nitrates and nitrites can bind to blood cells and prevent them from carrying oxygen to the body. They also can cause confusion, lightheadedness, vomiting and racing heart rate — possibly as part of an illness known as methemoglobinemia.
"Basically, people experience a lack of oxygen to their tissues and symptoms related to that," said Dr. Lucy Wilson, chief of the state health department's epidemiology center. Some of the Keswick workers tested positive for methemoglobinemia, while others didn't, she said.
Nitrates and nitrites are compounds of nitrogen and oxygen that can be found naturally, as a product of digestion of wastes containing nitrogen, according to the Environmental Protection Agency. They also are used in fertilizers, rodent poisons and preservatives often used for cured meats.
In boiler systems, used to heat water and air, the chemicals can be used to prevent steel corrosion. Boilers are pressurized containers in which water is heated. In some systems, the hot water passes around pipes that heat a separate supply of drinking water.
Two cases from New Jersey in the 1990s bear some similarities to the incident at the Keswick complex, Wilson said. In one case, dozens of elementary school children exhibited blueness of the fingertips and lips, nausea, vomiting and headaches. In another, six office workers showed the same symptoms.
In both cases, valves used to prevent water inside boilers from mixing with the potable water supply were found to be faulty. The boilers also were found to have been treated recently with nitrates and nitrites, according to Centers for Disease Control reports.
It took a "team effort" by epidemiologists and experts in building systems to narrow down the source of the illness, given how general the symptoms were and how many causes they might have had, Wilson said.
On Monday, as 600 people were evacuated from the complex's two buildings, carbon monoxide poisoning was the initial assumption, but fears ranged from explosives to food contamination.
Maryland Health Secretary Joshua Sharfstein called the quick evaluation process "impressive work" in a tweet sent Thursday.
Treatment for nitrate and nitrite exposure can include receiving oxygen through a mask, and, in serious cases, a dye known as methylene blue can be injected into the blood to restore its oxygen-carrying ability.
People usually do fairly well after they're removed from the source and treated, "as long as folks don't get too sick initially," said Bruce Anderson, an associate professor at the University of Maryland School of Pharmacy and director of operations for the Maryland Poison Center.
The Keswick complex, which houses about 1,050 workers, reopened Thursday, though some affected sinks, restrooms and other water sources were shut down. The affected water heater will be replaced, city health officials said.
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