(Reuters) - The home county to Flint, Michigan, where residents were exposed to lead-contaminated drinking water, had its first case reported this year of Legionnaires' disease, a respiratory infection that has been linked to the crisis, health officials said on Wednesday.

The Michigan Department of Health and Human Services said it was investigating the case in Genesee County and where the older adult resident, who has been hospitalized, may have been exposed.

"At this time, there is no indication that the individual was exposed within the city of Flint," the agency said in a statement.

At least 12 people have died in Flint due to Legionnaires' disease in cases that may be related to the lead-contaminated drinking water crisis, caused when Flint switched its tap water source to the Flint River in April of 2014 to save money. Flint switched back to the Detroit water system last October.

The outbreak in Genesee County began in 2014 after Flint stopped using Detroit's water system, which caused the crisis because the more corrosive water from the river leached lead from city pipes.

Legionnaires' is a type of pneumonia caused by inhaling mist infected with the bacteria Legionella and can lead to respiratory failure, kidney failure and septic shock. The mist may come from air conditioning units for large buildings, hot tubs or showers.

State auditors are investigating the state Health and Human Services department over its handling of the crisis and the rise in Legionnaires' disease cases.

Documents released in February show state officials knew about the Legionnaires' outbreak and suspected its link to the water crisis in Flint at least 10 months before a public announcement was made.

It was unclear how the water supply switch may have caused proliferation of the Legionella bacteria, but officials said in emails that efforts to combat contaminants by flushing the water system and using different treatment methods might have inadvertently promoted the bacteria.

(Refiles to fix typographical error in name of disease in headline)

(Reporting by Michael Hirtzer in Chicago; Editing by David Gregorio)