While health officials haven’t definitively pinpointed the exact source of the Legionnaires’ disease cluster in which 12 people have been sickened in McHenry County, IL, investigators have narrowed their probe for six cases.

The McHenry County Department of Health (MCDH), working in cooperation with the Illinois Department of Public Health (IDPH) and the Centers for Disease Control and Prevention (CDC), determined that six people infected with the respiratory illness either lived, worked or spent time within a 1½-mile radius of the intersection of Route 176 and Walkup Road in Crystal Lake.

Thus far, the inquiry into the activity of the other six provided investigators with no common connection.

The MCDH also announced that during its investigation, three additional cases were identified, increasing the case count to 12. Of the three new cases, two are from outside the county, and one is an out-of-state visitor to McHenry County.

Inquiry ongoing
The radius around the Crystal Lake intersection will serve as the focal point of the investigation, said MCDH community information coordinator Keri Zaleski. “Coming up with this case definition is very important,” she said.

The CDC is examining environmental samples from the area to determine the source of the Legionella bacteria.

“Many environmental samples have been collected,” acting MCDH administrator Joe Gugle said in a news release. “However, it is often the case that a single source is never found, which is not surprising or unusual considering that Legionella bacteria are pervasive in our natural environment.”

More cases unlikely
Seen more frequently in hot weather, Legionella are transmitted through mist or small droplets of water from freshwater environments such as lakes and streams.

Zaleski said that because the 10- to 14-day incubation period for Legionnaires’ disease has passed, the chances of future cases have decreased considerably.

First report
This outbreak first made headlines July 11, when the MCDH confirmed that nine residents of McHenry County had been sickened with Legionnaires’ disease in less than a month.

Residents of the cities of Algonquin, Crystal Lake, Huntley, McHenry and Wonder Lake were diagnosed with Legionnaires’ disease between June 7 and July 1. The ages of those sickened ranged from 46 to 82 years old.

“I can tell you eight people were hospitalized, (and) seven have been released,” Zaleski said in an email to the Woodstock Independent. “(Federal privacy) laws prevent any further information about this.”

Long-term-care facilities, other health-care providers, and local municipalities all have been alerted “as a precautionary measure,” Zaleski said.

LD increase
This outbreak represents a large spike in the incidence of Legionnaires’ disease in McHenry County. Last year, there were only four cases of Legionnaires’ disease in the county; there were nine cases in 2016 and three in 2015.

The northern-most border of McHenry County abuts Wisconsin. The county’s population is a little more than 300,000, which makes it Illinois’ sixth-most populous county.

Legionnaires’ info

Legionella bacteria grow best in warm water, and they are found primarily in human-made environments, including but not limited to: