After months of investigating, state health officials are confident a mysterious outbreak of a rare lung disease has its roots at the governor's mansion.

But they still don't have proof and other questions remain about how people were exposed to the disease at Terrace Hill.

State Epidemiologist Patricia Quinlisk says health officials are still awaiting test results to pin down the source of the histoplasmosis, an unusual but treatable lung disease.

The outbreak emerged more than four months ago when doctors began reporting cases. Eventually, there would be 36 confirmed cases and 12 probable ones.

Hundreds of pages of e-mails, correspondence and other documents obtained by The Associated Press under Iowa's freedom of information law, as well as interviews with health officials, show a methodical inquiry into the outbreak. The investigation led to the 139-year-old governor's mansion just west of downtown Des Moines.

Polk County doctors began reporting the disease, caused by an airborne fungi from bird or bat droppings, soon after the New Year's holiday.

Health officials worked to narrow the potential locations and connecting factors to the outbreak and determined many of those affected had attended an American Lung Association event at Terrace Hill on November 29th.

Officials say there was some construction at Terrace Hill around the time of the event and that might have been enough of a disturbance to put the offending spores in the air.

Governor Chet Culver and his wife, Mari Culver, were tested and do not have the illness.

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