When can you tell if you have a lung infection?

Chest x-ray. When you have lung infection, most likely it happened after cold or flu, most of the time you start to spike a fever, chills, sweeting, productive cough, those are signs of lung infection. The elderly people or the one had compromise immune system, they may not show these severe sings? Chest x-ray will confirm that.
Symptoms. Cough, sputum production, shortness of breath, fever, and chest pain on inspiration are the usual symptoms of lung infection ie. Pneumonia.