The disease frequently occurs in people whose resistance to infection has been reduced, but apparently healthy people may also develop the disease. People suffering from cancer or chronic kidney diseases are among those less able to fight infections. Chronic diseases, such as diabetes and alcoholism, also seem to increase vulnerability to Legionnaires' disease. Cigarette smokers are more likely to contract Legionnaire's disease, perhaps because smokers are generally more likely than non-smokers to develop respiratory tract infections. Legionnaire's is most often treated with the antibiotic drugs erthryomycin and rifampin.
Recovery often takes several weeks.
The likelihood of Legionella infection can be best reduced by good engineering practices in the operation and maintenance of air and water handling systems. Cooling towers and evaporative condensers should be inspected and thoroughly cleaned at least once a year. Corroded parts, such as drift eliminators, should be replaced. Algae and accumulated scale should be removed. Cooling water should be treated constantly.