Pneumonia is an infection of the lungs. It can be caused by bacteria, viruses, parasites and other organisms. Pneumonia is often spread by inhaling infected particles or by aspiration ("swallowing" into the lungs). It can spread through the blood stream to infect other parts of the body.
Some people may be at a higher risk of developing pneumonia. These include people with chronic lung disease, diabetes, immune suppression (which can occur with steroid use), the elderly and alcoholics. Consequently, pneumonia is often seen in someone with another condition - such as chronic lung disease - that made the body more susceptible to pneumonia infection.
Secondary infections (usually bacterial) of pneumonia itself may require that antibiotics be added or altered to treat the new organism. Rarely, a lung abscess may result from pneumonia. If excess fluid builds up in the sac around the lungs (pleural effusion), this also may need to be drained. Low blood sodium (hyponatremia) can also be a complication of bacterial pneumonia. Children are especially prone to this. In these cases, a person may need to be hospitalized for I.V. (intravenous) fluids. Many complications from pneumonia can be prevented by prompt medical care.