Pneumonia is an infection that inflames the air sacs in one or both lungs. The air sacs may fill with fluid or pus (purulent material), causing cough with phlegm or pus, fever, chills, and difficulty breathing. A variety of organisms, including bacteria, viruses and fungi, can cause pneumonia.
Pneumonia can range in seriousness from mild to life-threatening It is most serious for infants and young children, people older than age 65, and people with health problems or weakened immune systems.
Many germs can cause pneumonia. The most common are bacteria and viruses in the air we breathe. Your body usually prevents these germs from infecting your lungs. But sometimes these germs can overpower your immune system, even if your health is generally good.
Pneumonia is classified according to the types of germs that cause it and where you got the infection.
Community-acquired pneumonia is the most common type of pneumonia. It occurs outside of hospitals or other health care facilities. It may be caused by:
- Bacteria. The most common cause of bacterial pneumonia in the U.S. is Streptococcus pneumoniae. This type of pneumonia can occur on its own or after you’ve had a cold or the flu. It may affect one part (lobe) of the lung, a condition called lobar pneumonia.
- Bacteria-like organisms. Mycoplasma pneumoniae also can cause pneumonia. It typically produces milder symptoms than do other types of pneumonia. Walking pneumonia, a term used to describe pneumonia that isn’t severe enough to require bed rest, may be caused by M. pneumoniae.
- Viruses. Some of the viruses that cause colds and the flu can cause pneumonia. Viruses are the most common cause of pneumonia in children younger than 5 years. Viral pneumonia is usually mild. But in some cases it can become very serious.
- Fungi. This type of pneumonia is most common in people with chronic health problems or weakened immune systems, and in people who have inhaled large doses of the organisms. The fungi that cause it can be found in soil or bird droppings.
Some people catch pneumonia during a hospital stay for another illness. This type of pneumonia can be serious because the bacteria causing it may be more resistant to antibiotics. People who are on breathing machines (ventilators), often used in intensive care units, are at higher risk of this type of pneumonia.
Health care-acquired pneumonia
Health care-acquired pneumonia is a bacterial infection that occurs in people who are living in long-term care facilities or have been treated in outpatient clinics, including kidney dialysis centers. Like hospital-acquired pneumonia, health care-acquired pneumonia can be caused by bacteria that are more resistant to antibiotics.
Aspiration pneumonia occurs when you inhale food, drink, vomit or saliva into your lungs. Aspiration is more likely if something disturbs your normal gag reflex, such as a brain injury or swallowing problem, or excessive use of alcohol or drugs.
The signs and symptoms of pneumonia vary from mild to severe, depending on factors such as the type of germ causing the infection, and your age and overall health. Mild signs and symptoms often are similar to those of a cold or flu, but they last longer.
Signs and symptoms of pneumonia may include:
- Fever, sweating and shaking chills
- Cough, which may produce phlegm
- Chest pain when you breathe or cough
- Shortness of breath
- Nausea, vomiting or diarrhea
Newborns and infants may not show any sign of the infection. Or they may vomit, have a fever and cough, appear restless or tired and without energy, or have difficulty breathing and eating.
People older than age 65 and people in poor health or with a weakened immune system may have a lower than normal body temperature. Older people who have pneumonia sometimes have sudden changes in mental awareness.
When to see a doctor
See your doctor if you have difficulty breathing, chest pain, persistent fever of 102 F (39 C) or higher, or persistent cough, especially if you’re coughing up pus.
It’s especially important that people in these high-risk groups see a doctor:
- Children younger than age 2 with signs and symptoms
- Adults older than age 65
- People with an underlying health condition or weakened immune system
- People receiving chemotherapy or taking medication that suppresses the immune system
For some older adults and people with heart failure or chronic lung problems, pneumonia can quickly become a life-threatening condition.