Causes of pneumonia

Pneumonia is a common illness that affects millions of people each year. Germs called bacteria, viruses, and fungi may cause pneumonia. There are about 30 different causes of pneumonia. However, they all fall into one of these categories:

• Infective pneumonia: Inflammation and infection of the lungs and bronchial tubes that occurs when a bacteria (bacterial pneumonia) or virus (viral pneumonia) gets into the lungs and starts to reproduce.
• Aspiration pneumonia: An inflammation of the lungs and bronchial tubes caused by inhaling vomit, mucous, or other bodily fluids. Aspiration pneumonia can also be caused by inhaling certain chemicals.

Infective Pneumonia

Pneumonia caused by bacteria tends to be the most serious. The most common cause of bacterial pneumonia in adults is a bacteria called Streptococcus pneumoniae or Pneumococcus. Pneumococcal pneumonia occurs only in the lobar form.
An increasing number of viruses are being identified as the cause of respiratory infection. Half of all pneumonias are believed to be of viral origin. Most viral pneumonias are patchy and the body usually fights them off without help from medications or other treatments.
Pneumococcus can affect more than the lungs. The bacteria can also cause serious infections of the covering of the brain (meningitis), the bloodstream, and other parts of the body.

Aspiration Pneumonia

Inhaling vomit, irritating fumes, or other substances can result in aspiration pneumonia. Agents such as petroleum solvents, dry cleaning fluid, lighter fluid, kerosene, gasoline, and liquid polishes and waxes are the most likely causes. Pulmonary edema, or fluids in the lung from injury, can develop rapidly. With repeated exposure, the lungs may lose elasticity and small airways may become obstructed. This can lead to increased reactive airway disease and chronic lung disease in adults.

Transmission

Ways you can get pneumonia include:

• Bacteria and viruses living in your nose, sinuses, or mouth may spread to your lungs.
• After breathe some of these germs directly into your lungs. This generally occurs during sleep.
• You breathe in (inhale) food, liquids, vomit, or secretions from the mouth into your lungs (aspiration pneumonia)
• During or after a viral upper respiratory infection, such as a cold or influenza (flu).
• As a complication of a viral illness, such as measles or chickenpox.
• If you breathe large amounts of food, gastric juices from the stomach, or vomit into the lungs (aspiration pneumonia). This can happen when you have had a medical condition that affects your ability to swallow, such as a seizure or stroke.

You can get pneumonia in your daily life, such as at school or work (community-associated pneumonia) or when you are in a hospital or nursing home (healthcare-associated pneumonia). Treatment may differ in healthcare-associated pneumonia because bacteria causing the infection in hospitals may be different from those causing it in the community.