A late start to summer weather in the Upper Midwest may be linked to an outbreak of 27 cases of Legionnaire's disease in Milwaukee County since June 1 of this year, a health official said on Thursday.
The outbreak includes 19 cases of the illness, a severe form of pneumonia, among Milwaukee residents, according to the city's health department. Two other county cases are suspected.
The disease is contracted by breathing in a mist or vapor contaminated with the Legionella bacteria, which can grow in cooling towers, showers, decorative fountains and other water sources. People already in poor health, including those who smoke heavily and have chronic lung disease, are the most vulnerable.
The Milwaukee outbreak may be linked to cooling towers on large buildings, according to Paul Biedrzycki, director of disease control and environmental health for the Milwaukee Health Department. They are typically readied for hot weather in late April and early May, but were turned on later this year because warm weather arrived unusually late, he said.
The delay, which left the towers without maintenance, may have allowed for the growth of the bacteria.
"I think this is an interesting hypothesis," Biedrzycki said. He said health officials may never know for sure.
The number of illnesses is unusual - the county typically sees 24-27 cases for the entire year.
The rate of reporting in Milwaukee dropped slightly in the last week, so Biedrzycki said the area "may be out of the woods." There have been no deaths.
The illness is named for a 1976 outbreak at an American Legion convention in Philadelphia.
Three deaths were tied to a Legionnaire's outbreak in a Chicago hotel last summer. Biedrzycki said that the disease tends to be more lethal when it is from a source inside a building.