Updated: 4:21 p.m. | Posted: 12:39 p.m.
A beverage processing plant in Hopkins has been identified as the likely source of a Legionnaires' disease outbreak in that community.
Samples from a single cooling tower at Citrus Systems, Inc., contained Legionella bacteria, which causes Legionnaires' disease, public health investigators said Wednesday. The company's products aren't affected.
Grow the Future of Public Media
MPR News is supported by Members. Gifts from individuals power everything you find here. Make a gift of any amount today to become a Member!
The bacteria exactly matched the strain taken from patients who contracted the respiratory infection, according to the Minnesota Department of Health.
The company's cooling tower is located in the heart of Hopkins' Legionnaires' cases, said Richard Danila, deputy state epidemiologist.
"Some [cases were] within a block or two and others a little further away," said Danila.
Twenty-three people were sickened in the outbreak. One person died. All of them lived or worked in Hopkins, or visited the city during the 10 days before they became ill.
The outbreak is considered over, though the Health Department says there's still a remote chance that more cases of illness could emerge. The Hopkins cases nearly broke a Legionnaires' outbreak record for the state set two decades ago.
In 1995 a Legionnaires' disease cluster in Luverne climbed to 24 confirmed cases — the most ever in Minnesota. That same summer a separate outbreak in Mankato sickened 17 people.
Legionnaires' disease is contracted by inhaling water mist contaminated with Legionella bacteria. Cooling towers are often identified as a breeding ground for the bacteria. That was the source of the 1995 outbreaks in Luverne and Mankato, Danila said.
"We know from previous outbreaks that the water mist from these cooling towers can be picked up by the wind and carried some distance," Danila said. "And within that mist would be the bacteria that you would breathe deep into your lungs."
The Health Department said Citrus Systems already works with a qualified contractor to maintain its cooling system.
Investigators don't know what went wrong at the cooling plant.
"These cooling towers are complicated systems and it's not clear exactly what leads to growth sometimes," Danila said. "Sometimes there's an obvious break in disinfection, but that was not the case here. This was a fully functioning, fully maintained system."
The company has disinfected its cooling towers and will set up a routine testing schedule to make sure Legionella doesn't return, Danila said.
Cooling towers at other Hopkins businesses were also sampled as part of the investigation, but the Health Department said none had the specific Legionella strain linked to the outbreak.