By Jeremy Ross

Chicago (CBS) — Residents of the senior living community in McHenry County where three cases of Legionnaires’ disease were confirmed this month received a letter dated yesterday letting them know the source of the disease has been identified.

McHenry Villa is taking precautions as a result of the outbreak , which resulted in one death.

RELATED Another Legionnaires’ Disease Cluster Found In McHenry County

The letter stated health officials completed an environmental investigation and plumbing inspection last week, which confirmed the presence of Legionella bacteria in the building’s water system. As a result, McHenry Villa received a violation notice from the Illinois Department of Public Health.

The former mayor of McHenry, 91-year-old Donald Doherty, died of the Legionnaires’ Nov. 21

Legionnaires can result in a serious lung infection that people can get by breathing in small droplets of water containing Legionella bacteria.

Today, CBS 2 spotted a large truck in the nursing home lot. It’s unclear whether the truck was there to address the health issue.

Some residents allegedly moved to a nearby hotel while others who remain at McHenry Villa are advised to take precautions, like taking baths instead of showering to minimize contact with water vapor.