Legionnaire's disease is a particularly severe cause of bacterial pneumonia. Viral respiratory infections precede bacterial infections in up to one-half of patients with pneumonia. Therefore, prevention and early treatment of influenza is an important strategy to reduce the incidence and consequences of pneumonia. Even healthy people have disease-causing bacteria like Pneumococcus living in the back of the throat and mouth during the winter months. In some parts of the world, fungi like Histoplasmosis or Coccidiomyccosis are common causes of pneumonia.
Tuberculosis is usually a chronic pneumonia, but can mimic many other common respiratory infections.
Physicians must remain vigilant for tuberculosis, as this may account for many cases of pneumonia and is treatable when recognized. Pneumonia may come on suddenly or gradually. Shortness of breath may develop in severe cases. In the very old, symptoms may be less obvious and complaints may include only loss of concentration or worsening appetite. In addition, depending on the type of microorganism, people may take from seven to twenty days for the illness to progress.