Occult pneumonia is a pneumonia that is not observable directly by the eye, but can only be shown indirectly, especially by radiography. Occult pneumonia can be made visible by chest X-rays. The general symptoms cough for more than 10 days and fever for more than 3 days can indicate the presence of occult pneumonia, just as a temperature of 39°C or higher and a high white blood cell count. Although pneumococcal vaccination lowers the prevalence of occult pneumonia, it does not make radiographic diagnosis superfluous at patients with prolonged fever, cough or leukocytosis.