Symptoms. The symptoms of Legionnaires’ disease begin within two to 10 days after the person is exposed to the bacteria. At first the symptoms resemble the flu, with aches and pains, a high fever and a headache. As the disease progresses, the patient develops a cough that may bring up mucus or blood-stained mucus, difficulty breathing, chest pain, diarrhea along with nausea and vomiting and mental confusion. The disease not only affects the lungs but can attack the heart and cause wounds to become infected, but this is rare.