Final answer:
The diagnosis for a 55-year-old man who is a smoker and a heavy drinker presenting with new cough and flulike symptoms, with gram-negative rods seen on a silver stain of sputum, is Legionnaires' disease.
Step-by-step explanation:
The question asked is: A 55-year-old man who is a smoker and a heavy drinker presents with a new cough and flulike symptoms. Gram stain shows no organisms; silver stain of sputum shows gram-negative rods. What is the diagnosis?
The diagnosis for the 55-year-old man presenting with a new cough and flu-like symptoms, along with gram-negative rods seen in the silver stain of sputum, is Legionnaires disease. Legionnaires disease is caused by the bacteria Legionella pneumophila. It is a fastidious bacterium that is difficult to culture, and its cells do not efficiently stain with the Gram stain, requiring other staining techniques for visualization.