Pneumonia

Definition
Pneumonia is a lung infection that can be caused by various microorganisms.

Causes/associated factors
In the United States, about 4 to 5 million people develop pneumonia every year. It can range from a mild complication of an upper respiratory infection to a life-threatening illness. Sadly, pneumonia is the seventh leading cause of death in the United States. Symptoms, treatment and outcome depend on the type of pneumonia involved, as well as your general health.
Those at highest risk of developing pneumonia include the very young, the very old, and those who have illnesses or conditions that affect the immune system or the lungs, such as:

HIV, AIDS or other immune-deficiency diseases
cancer, diabetes, kidney or liver disease, spleen removal or sickle cell anemia
alcoholism or intravenous (IV) drug use
malnutrition
chronic obstructive pulmonary disease, asthma or cystic fibrosis
Other risk factors include:

major surgery
smoking
aspiration (inhaling fluids or foreign substances into the breathing passages) due to problems such as swallowing difficulties or altered level of consciousness
treatments that suppresses the immune system, such as corticosteroid therapy, chemotherapy and radiation therapy
viral respiratory infections, such as colds or the flu
The three leading causes of pneumonia are bacteria, viruses and mycoplasma, but a host of other organisms can also be responsible for this illness.

Bacterial pneumonia is caused by a variety of bacteria, such as Streptococcus pneumoniae, Haemophilus influenzae (Hib), Staphylococcus, Chlamydia and Legionella. It affects people of all ages, with some bacteria affecting certain age groups more than others. Pneumococcal pneumonia, caused by S. pneumoniae, is the most common type of bacterial pneumonia. It occurs more often in young children, older adults, and those who have chronic illnesses or weak immune systems. This type of pneumonia can lead to serious illness.

Viral pneumonia is more commonly caused by the influenza A and B viruses and the respiratory syncytial virus (RSV). Many other viruses, such as parainfluenza virus, adenovirus, varicella-zoster virus (the virus that causes chickenpox), herpes virus and cytomegalovirus (CMV), can also cause pneumonia. Viral pneumonia is more common in infants and children, but it can also affect adults. Viral respiratory infections, such as colds or the flu, can make the lungs more susceptible to bacterial invasion and, thus, bacterial pneumonia.

Mycoplasma pneumonia is typically mild and sometimes referred to as walking pneumonia. It's caused by Mycoplasma pneumoniae, an organism that has characteristics of both viruses and bacteria. This type of pneumonia is most common in children and young adults. Community outbreaks can occur.
Fungi and parasites can also cause pneumonia. Fungi, such as Pneumocystis carinii, more commonly cause illness in people who have weak immune systems. Pneumocystis carinii pneumonia (PCP) is often severe and may be the first sign of infection with the AIDS virus.

Various organisms affect the lungs differently. Some cause concentrated areas of infection in one or more lobes (major divisions) of one or both lungs -- the left lung has two lobes and the right lung has three. This is referred to as lobar pneumonia. Others produce scattered areas of infection throughout the lungs, which is known as bronchial pneumonia. When both lungs are affected, the condition is referred to as double pneumonia.


Transmission
Most cases of pneumonia are thought to be contracted by inhaling organisms that are coughed or sneezed into the air by an infected person. Sometimes, bacteria that are normally present in the mouth, throat or stomach are swallowed into the lungs. This is more common in people who have difficulty with swallowing or alertness. It can also occur in people who are healthy, however. This type of pneumonia may be called aspiration pneumonia. Much less frequently, organisms come directly from nearby infection sites or are carried in the blood from distant infection sites.
The incubation period (time from exposure until symptoms develop) varies with the organism causing the infection. For example, for pneumococcal pneumonia it may be as short as one to three days, but for mycoplasma pneumonia it's six to 32 days.


Signs/symptoms
Symptoms of pneumonia can vary greatly. For example, pneumonia that follows a minor upper respiratory infection in an otherwise healthy young adult might cause symptoms no worse than those of an ordinary cold. However, a virulent strain of influenza can cause severe symptoms and become fatal for a susceptible person within 24 hours.
Generally, early symptoms may include fever and chills, followed by:

cough that produces blood-streaked, yellowish-white or green phlegm
chest pain that worsens when coughing or breathing deeply
shortness of breath
rapid breathing
fatigue
Other symptoms may include:

sweats
headache
muscle aches
nausea, vomiting or diarrhea
cyanosis (a bluish tinge to the skin or fingernails)
mental confusion and, occasionally, delirium

Diagnosis
The doctor will review your medical history and current symptoms, and do a physical exam. The doctor will listen to your lungs for wheezing, crackling or diminished breathing, which may indicate fluid accumulation in the lungs. You may also need chest X-rays to confirm the diagnosis. If the illness is in an early stage or you're dehydrated, however, it's possible for the X-rays to appear normal when you actually have an infection. A normal chest X-ray can also occur with Pneumocystis carinii pneumonia, a condition seen most often in people who have AIDS.
You may need other tests to confirm the diagnosis, possibly including complete blood cell counts or other specialized blood tests, as well as lab studies of secretions from your nose or lower respiratory tract. If you have fluid in the sac surrounding your lungs, thoracentesis may be done. With this procedure, fluid is drawn directly from the chest wall for further lab analysis.


Treatment
Treatment will depend on the organism responsible for your infection. Bacterial and mycoplasma pneumonia are treated with antibiotics. Some viral pneumonias respond to antiviral medications. However, treatment is often begun before the specific organism can be identified. To choose the best medication, your doctor will evaluate various factors, such as your age, other health problems and symptoms, as well as patterns of illness in the community. If the specific organism is later identified, your medication may be changed. For example, you may be given antibiotics until your doctor confirms you have a viral infection. For bacterial pneumonia, early antibiotic treatment can prevent complications from developing.
Depending on the severity of your illness, your doctor may suggest resting and drinking plenty of fluids. Medications to relieve pain, reduce fever, expectorate mucus, and open your airways (known as bronchodilators) may also be recommended, as well as coughing and deep-breathing exercises. Your doctor may suggest follow-up visits to evaluate the effectiveness of your treatment and check for relapses.

In severe cases of pneumonia, hospitalization may be necessary. There you may receive medication, fluids or other nutritional support through an IV. You may need oxygen or help with breathing, and your lungs may need to be suctioned. Doctors who specialize in lung infections or infectious diseases may be consulted for complex treatment decisions.


Complications
Left untreated, pneumonia can lead to potentially fatal complications such as septic shock (a severe infection in the bloodstream), hypoxemia (lack of oxygen in the blood) and respiratory failure. Within your lungs, the infection may also lead to empyema (pus in the membrane surrounding the lungs) or a lung abscess (collection of pus). If the bacteria enter your bloodstream and travel to other organs, you can develop septic arthritis (inflammation of a joint), endocarditis (inflammation of the membrane that lines the heart), pericarditis (inflammation of the membrane surrounding the heart) or meningitis (inflammation of the membranes surrounding the brain or spinal cord).

Pregnancy-specific information
Pregnancy does not increase the risk of developing pneumonia. Some types of pneumonia, however, may be more severe during pregnancy -- especially viral pneumonia. The risk of preterm labor, delivery and possibly other pregnancy complications may also be higher. Discuss any symptoms suggestive of pneumonia with your doctor. As a precaution, avoid contact with anyone who has a viral infection or other active illness while you're pregnant. Your doctor may also recommend the influenza (flu) vaccine or other preventive measures.

Senior-specific information
Again, the risk of developing penumonia increases with age. Older adults are more susceptible to S. pneumoniae and face a higher risk of severe illness, complications or even death. Pneumococcal pneumonia is a common cause of hospitalization among older adults. The disease may have a more gradual onset and present with symptoms such as fatigue, weakness, appetite loss, abdominal pain, confusion, a general decline in functioning or falling more often. Common symptoms, such as cough, fever and shortness of breath, are often absent in elderly adults. Efforts to prevent pneumonia are extremely important. It is highly recommended that older adults receive the pneumococcal vaccine and an annual flu vaccine. Consult your doctor for further details.

Prevention
To prevent pneumonia, avoid people who have respiratory infections or the flu, and wash your hands often. Also, eat healthfully and get plenty of rest and regular exercise. If you smoke, quit. Avoid secondhand smoke whenever possible. If you're confined to bed or recovering from surgery, exercise your lungs with deep breathing and coughing exercises.
To help prevent aspiration pneumonia in infants and children, be sure to make age-appropriate food selections. Proper positioning while nursing or drinking from a bottle is also important. At any age, dietary modifications may be helpful if you have certain neuromuscular disorders. Since aspiration pneumonia may also develop in people who become intoxicated (they can vomit and then inhale their stomach contents), intoxication should be avoided.

The pneumococcal vaccine and a yearly flu vaccine may also help prevent pneumonia in some people. The pneumococcal vaccine is now recommended for all young children and has decreased the rate of pneumococcal pneumonia in this age group. It's also recomemended for everyone over age 65. If you're under age 65, you should consider vaccination if you're at high risk of pneumonia. Consult your doctor to see if earlier vaccination is appropriate for you. Most people only receive the pneumococcal vaccine once. Depending on individual circumstances, however, your doctor may recommend a second vaccination.

The flu vaccine is recommended for everyone over age 50. If you're under age 50, consider getting a yearly flu shot if you're in a high-risk group (you have diabetes, asthma, heart disease, kidney disease or a weak immune system), or you're pregnant and will be past the third month of pregnancy during the flu season. The vaccine is also encouraged for young children and their families. Those who receive the vaccine are less likely to develop complications from the flu virus, such as pneumonia. Consult your doctor to see if annual vaccination is appropriate for you.