Organ Specific Infections Lung infections are one of the most common medical conditions , especially among elderly people across the world. . How Lung Infection Occurs Pneumonia happens when bacteria, viruses, and less commonly fungi collect in a person's air sacs and begin to grow. The air sacs may become filled with pus and fluid, which can make breathing more difficult, cause chest pain, and lead to a cough that is different from a person's usual chronic cough associated with their disease. Bacterial and some of viral pneumonia may be prevented through proper vaccinations. Symptoms of a Lung Infection Fever Increased Shortness of Breath Productive Cough Changes in Mucus Pleuritic Chest Pain Asthma