Understanding Pneumonia

What is pneumonia?

Pneumonia is an infection in one or both of your lungs. Many small germs, such as bacteria, viruses, and fungi, can cause pneumonia.  Pneumonia is not a single disease. It can have more than 30 different causes. Understanding the cause of pneumonia is important because pneumonia treatment depends on its cause.

Approximately one-third of the pneumonia cases in the United States each year are caused by respiratory viruses. These viruses are the most common cause of pneumonia in children younger than 5 years.

The flu virus is the most common cause of viral pneumonia in adults. Other viruses that cause pneumonia include respiratory syncytial virus, rhinovirus, herpes simplex virus, severe acute respiratory syndrome (SARS), and more.

How does Pneumonia affect your Body?

Most of the time, the body filters germs out of the air that we breathe. This keeps the lungs from becoming infected. But germs sometimes find a way to enter the lungs and cause infections. This is more likely to occur when:

  • Your immune system is weak.
  • A germ is very strong.
  • Your body fails to filter germs out of the air that you breathe.

When the germs that cause pneumonia reach your lungs, the lungs' air sacs (alveoli) become inflamed and fill up with fluid and pus. This causes the symptoms of pneumonia, such as a cough, fever, chills, and trouble breathing.

When you have pneumonia, oxygen has trouble reaching your blood. If there is too little oxygen in your blood, your body cells can't work properly. Because of this and infection spreading through the body, pneumonia can cause death.

Pneumonia affects your lungs in two ways. Lobar pneumonia affects a section (lobe) of a lung. Bronchial pneumonia (or bronchopneumonia) affects patches throughout both lungs.

What causes Pneumonia?

Many small germs can cause pneumonia. There are five main causes of pneumonia:

  • Bacteria
  • Viruses
  • Mycoplasmas
  • Other infectious agents, such as fungi - including pneumocystis
  • Various chemicals

If you have viral pneumonia, you also are at risk of getting bacterial pneumonia.

What are the Different types of Pneumonia?

Bacterial Pneumonia

Bacterial pneumonia can attack anyone, at any age.

Bacterial pneumonia can occur on its own or develop after you've had a cold or the flu.

People at greatest risk for bacterial pneumonia include people recovering from surgery, people with respiratory diseases or viral infections and people who have weakened immune systems.

If your body's defenses are weakened—by illness, old age, malnutrition, or impaired immunity—the pneumonia bacteria, which can live in healthy throats, can multiply and work their way into the lungs. The infection can quickly spread through the bloodstream and invade the entire body.

Dozens of different types of bacteria can cause pneumonia.

  • The most common cause of bacterial pneumonia in adults is Streptococcus pneumoniae (pneumococcus), but there is a  vaccine available for this form of pneumonia.
  • Atypical pneumonia, often called walking pneumonia, is caused by bacteria such as Legionella pneumophila, Mycoplasma pneumoniae, and Chlamydophila pneumoniae.
  • Pneumocystis jiroveci pneumonia is sometimes seen in people whose immune system is impaired (due to AIDS or certain medications that suppress the immune system).
  • Other bacteria that can cause pneumonia include Staphylococcus aureus, Moraxella catarrhalis, Streptococcus pyogenes, Neisseria meningitidis, Klebsiella pneumoniae, and Haemophilus influenzae.

Viral Pneumonia

Most respiratory viruses attack the upper respiratory tract, but some cause pneumonia, especially in children.  Most of these pneumonias are not serious and last a short time but others can be severe.

Viral pneumonia caused by the influenza virus may be severe and sometimes fatal. The virus invades the lungs and multiplies; however, there are almost no physical signs of lung tissue becoming filled with fluid. This pneumonia is most serious in people who have pre-existing heart or lung disease and pregnant women.

In extreme cases, the patient has a desperate need for air and extreme breathlessness. Viral pneumonias may be complicated by an invasion of bacteria, with all the typical symptoms of bacterial pneumonia.

 Mycoplasma Pneumonia

Mycoplasms are the smallest free-living agents of disease in humankind. They are not classified as to whether they are bacteria or viruses, but they have traits of both.

Mycoplasms cause a mild and widespread pneumonia. They affect all age groups, but occur most often in older children and young adults.

Other Types of Pneumonia

Tuberculosis can cause pneumonia (tuberculosis pneumonia). It is a very serious lung infection and extremely dangerous unless treated early.

Pneumocystis carinii pneumonia (PCP) is caused by an organism believed to be a fungus. PCP may be the first sign of illness in many persons with AIDS.

PCP can be successfully treated in many cases. It may recur a few months later, but treatment can help to prevent or delay recurrence.

Other less common pneumonias may be quite serious and occur more often. Various special pneumonias are caused by the inhalation of food, liquid, gases or dust, and by fungi.

Rickettsia (also considered an organism somewhere between viruses and bacteria) cause Rocky Mountain spotted fever, Q fever, typhus and psittacosis, diseases that may have mild or severe effects on the lungs.

How serious is pneumonia?

Pneumonia can be very serious and can cause death.

Pneumonia tends to be more serious for infants and young children, older adults (people 65 years or older), people who have other chronic health problems, and people who have weak immune systems as a result of diseases or other factors.

If you develop pneumonia, your chances of a fast recovery are greatest if:

  • you are young
  • your pneumonia is caught early
  • your immune system—your body's defense against disease—are working well
  • the infection hasn't spread
  • you are not suffering from other illnesses

With treatment, most patients will improve within two weeks. Elderly or debilitated patients may need longer treatment.

If you have taken antibiotics, your doctor may want to make sure your chest x-ray becomes normal again after you finish the whole prescription. It may take many weeks for your x-ray to clear up.

Possible Complications

People who may be more likely to have complications from pneumonia include:

  • Older adults or very young children
  • People whose immune system does not work well
  • People with other, serious medical problems such as diabetes or cirrhosis of the liver

Possible complications include:

  • Respiratory failure, which requires a breathing machine or ventilator
  • Sepsis, a condition in which there is uncontrolled swelling (inflammation) in the body, which may lead to organ failure
  • Acute respiratory distress syndrome (ARDS), a severe form of respiratory failure
  • Emphysema or lung abscesses—These are infrequent, but serious, complications of pneumonia. They occur when pockets of pus form inside or around the lung. These may sometimes need to be drained with surgery.

Who gets pneumonia?

Anyone can get pneumonia, but some people are at a higher risk than others to get pneumonia.

Risk factors (that increase your chances of getting pneumonia) include:

  • Cigarette smoking
  • Recent viral respiratory infection—a cold, laryngitis, influenza, etc.
  • Difficulty swallowing (due to stroke, dementia, Parkinson's disease, or other neurological conditions)
  • Chronic lung disease such as COPD, bronchiectasis, or cystic fibrosis)
  • Cerebral palsy
  • Other serious illnesses, such as heart disease, liver cirrhosis, or diabetes  
  • Living in a nursing facility
  • Impaired consciousness (loss of brain function due to dementia, stroke, or other neurologic conditions)
  • Recent surgery or trauma
  • Having a weakened immune system due to illness, certain medications, and autoimmune disorders