Pneumonia is an infection or inflammation of the lungs, where the air sacs (alveoli) of the lungs become filled with fluid. Pneumonia is very common and can be caused by a variety of factors. Most cases of pneumonia are either caused by bacteria or a virus, and are most likely to occur after a bout of influenza or a cold. However, there are many microorganisms that can cause pneumonia such as mycoplasms, fungi or chemical agents. Because of the variety of microorganisms that can cause pneumonia, in many cases of pneumonia the specific cause is never determined, even after extensive testing.
In the early 20th century, pneumonia was the leading cause of death in the United States. Pneumonia can now often be treated effectively with antibiotics. However, it is still a serious medical condition that may be fatal in some people. Pneumonia (along with influenza) is among the most common causes of death in the United States, according to the U.S. Centers for Disease Control and Prevention (CDC).
Bacteria, viruses and other organisms frequently enter the body through the nose and mouth. In most healthy people, these microorganisms are prevented from reaching the lungs by a variety of defenses such as the immune system, the cough reflex and small hair-like structures called cilia that line the bronchial tubes. These germs are usually either completely destroyed or severely weakened by the immune system. Sometimes, if they have not been destroyed, the germs can remain dormant in the throat. If the immune system then becomes compromised, it is possible for the germs to become active and progress through the respiratory system into the lungs. After the germs are in the lung’s air sacs, they can cause the sacs to become inflamed and fill with pus and mucus while the immune system attempts to fight the infection. This makes it difficult to breathe comfortably and can stop oxygen from entering the bloodstream, which makes the rest of the body unable to work efficiently.
Pneumonia may affect one lung or one section (lobe) of one lung. This is called lobar pneumonia. If the pneumonia affects sections of both lungs it is called bronchial pneumonia or double pneumonia.
Sometimes, pneumonia is classified according to criteria such as where or how it was transmitted or the severity of the symptoms. Some common classifications of pneumonia include:
- Community-acquired pneumonia (CAP). Pneumonia that is transmitted within the general community. Community-acquired pneumonia is one of the most common classifications of pneumonia.
- Hospital-acquired pneumonia. Pneumonia that is transmitted while in institutional (hospital) care (nosocomial infections). Hospital-acquired pneumonia is considered more severe than pneumonia contracted elsewhere. The strains of bacteria that are transmitted in hospitals are more likely to have developed antibiotic resistance and are difficult to treat. People who develop pneumonia in the hospital are also more likely to have a weakened immune system and so are less able to fight the infection.
- Aspiration pneumonia. Pneumonia that is contracted by breathing in toxic particles. If the particles break through the defenses of the respiratory system, they can cause infection in the lungs. Aspiration pneumonia is most often contracted after vomiting. People who vomit while unconscious are most at risk from aspiration pneumonia.
- Walking pneumonia. Pneumonia with mild symptoms. Mycoplasma pneumonia is often described as walking pneumonia because of its notoriously mild symptoms that rarely require substantial bed rest.
Pneumonia is more common and more severe in children, older adults and people with compromised immune systems. The bacteria that cause streptococcus pneumonia are particularly dangerous for children. These bacteria are also the leading cause of meningitis in children.
Pneumonia is a complex condition to classify. It is normally the result of other infections rather than being a disease in its own right. Pneumonia can also be caused by many microorganisms. Most physicians identify three main types of pneumonia: bacterial, viral and mycoplasma. Mycoplasma are tiny organisms that behave similarly to bacteria and viruses. However, there are many more causes of pneumonia, including some fungi and chemical agents.
Bacterial pneumonia is caused by bacteria infecting the lungs. Most people normally have potentially dangerous bacteria in their nose and throat, but they rarely infect the lungs. However, when the immune system is compromised, these bacteria have the opportunity to multiply and cause an infection. Bacterial pneumonia can occur while the body is recovering from influenza (flu). In the United States, bacterial pneumonia is most often caused by the bacteria Streptococcus pneumoniae. Streptococcal pneumonia can easily spread to other parts of the body where it can cause further problems such as meningitis, bacteremia (bacteria in the blood) and otitis media (middle ear infection). Bacterial pneumonia can usually be effectively treated with antibiotics.
Viral pneumonia accounts for up to half of pneumonia cases in the United States. It is commonly caused by an influenza virus. Therefore, most cases of viral pneumonia are reported in the winter, when influenza viruses are predominant. People with viral pneumonia are also at a high risk of developing bacterial pneumonia. Viral pneumonia is more serious in people with chronic illnesses such as cardiovascular or lung disease, as well as pregnant women. Because antibiotics cannot treat viruses, there are limited treatment options available for viral pneumonia. Most cases clear up over a certain period of time with supportive care.
Mycoplasma pneumonia is sometimes called walking pneumonia because its symptoms are often mild and may not require bed rest. The lungs are invaded by tiny organisms called mycoplasms. These were initially thought to be viruses, but are now understood as being neither bacteria nor viruses, but organisms that behave a little like both. Mycoplasma pneumonia spreads easily in places where people have close contact, such as day care centers and schools. Studies have suggested that mycoplasma pneumonia could account for up to one-third of all childhood cases of pneumonia.
In addition to the three main types of pneumonia, there are many other types that may affect portions of the population. These include:
- Fungal pneumonia. Various types of fungi can cause pneumonia. Some of these fungi are only found in certain parts of the United States. For example, the Histoplasma capsulatum fungus is only found in the Mississippi River and Ohio River valleys and Coccidioides immitis fungi only occur in the semiarid climate of the southwestern United States. Symptoms can vary in cases of fungal pneumonia but are often only mild. Some types of fungal pneumonia produce no symptoms at all. Fungal pneumonia is often more serious in people with impaired immune systems.
- Pneumocystis jiroveci pneumonia (PCP). Previously called pneumocystis carinii pneumonia. This type of pneumonia is particularly dangerous for people with HIV or AIDS. It is caused by a fungus that is not normally harmful for healthy people but can cause lung infections in people with severely compromised immune systems. Often, the first sign that someone has developed AIDS is the diagnosis of PCP. PCP can be prevented using antibiotics.
- Chlamydia pneumonia. This type of pneumonia is most common in school-aged children and has mild symptoms, similar to mycoplasma pneumonia. It can normally be effectively treated with antibiotics.
Pneumonia can affect any person at any stage of life, even if they are otherwise healthy. Any factors that compromise the ability of the immune system to fight infection, or anything that adversely affects lung function, can significantly increase the risk of contracting pneumonia. Factors that could increase the risk of pneumonia include:
- Age. Pneumonia is more common and sometimes more severe in children and older adults. This is because the immune systems of children have often not matured enough to fight strong infections and the immune systems of older adults have often been weakened by age and other medical conditions. Also, children and older adults tend to spend more time in close contact with many other people and so are more likely to be in areas where bacteria and viruses are spread. For example, pneumonia can spread quickly in day care facilities and nursing homes.
- HIV/AIDS. HIV (human immunodeficiency virus) and AIDS (acquired immunodeficiency syndrome) are major risk factors for many infections, including pneumonia. When someone has HIV or AIDS, their immune system is seriously impaired. This means that many viruses or bacteria that are usually harmless for healthy people can result in serious illness for people with HIV or AIDS. People with these conditions are particularly at risk for pneumocystis jiroveci pneumonia (PCP) and are encouraged to take medication to prevent it.
- Other chronic diseases. Certain illnesses can also impair the immune system and increase the risk of pneumonia. These include:
- Cardiovascular disease
- Lung diseases such as emphysema
- Diabetes mellitus
- Sickle cell anemia
Additionally, people undergoing chemotherapy for cancer, as well as those who have had organs removed or transplanted, are at an increased risk for pneumonia. Other risk factors include:
- Extended stays in healthcare facilities. People who spend time in hospitals are at considerable risk for hospital-acquired pneumonia. This is especially the case for those who spend time in the intensive care unit or are aided in breathing by a mechanical respirator. Mechanical breathing devices may bypass many of the defense mechanisms that the body has to keep germs from entering the lungs. Also, strains of pneumonia contracted while hospitalized can be more dangerous than other types of pneumonia because of the increased likelihood that they have become resistant to certain antibiotics.
- Smoking. Smoking has a devastating effect on many parts of the body, especially the respiratory system. Smoking can damage the fine hair-like structures (cilia) that line the bronchial tubes and trap contaminants that enter through the mouth and nose. It can also damage the air sacs (alveoli) and the lining of the lungs. In addition, smoking suppresses the immune system, making it harder to fight off infections.
- Alcoholism or drug abuse. People who abuse alcohol or other drugs are at an increased risk of pneumonia for a number of reasons. Alcohol and drugs weaken the immune system, making it easier for germs to enter the respiratory system. Also, people who lose consciousness from excess alcohol or drugs are more likely to inhale vomit or other toxins from the stomach, which can lead to aspiration pneumonia.
The causes of pneumonia are varied. Physicians often find that they may not be able to identify the cause even after extensive testing. Some causes of pneumonia include:
- Bacteria such as Streptococcus pneumoniae, Haemophilus influenzae or Legionella pneumophila (the bacteria that causes Legionnaire’s disease).
- Viruses such as influenza, measles or chickenpox.
- Fungi such as Histoplasma capsulatum or Coccidioides immitis.
- Parasites such as Toxoplasma gondii or Ascariasis.
- toxins from the stomach that have been inhaled into the respiratory system.
- Chemical toxins such as pesticides or gasoline.
The symptoms of pneumonia are similar to the symptoms of a severe cold or influenza (flu). The similarity of symptoms results in pneumonia being difficult to recognize, especially in people who have already been diagnosed with the flu. The symptoms of pneumonia also differ depending on the strength of the immune system and the cause of the pneumonia. Symptoms can begin to appear from several hours to a few days after the initial infection.
Most types of pneumonia may produce the following signs and symptoms:
- Persistent cough
- Green or rust-colored mucus (sputum)
- Fever with shaking chills
- Sharp pain in the chest while breathing deeply or coughing
- Rapid breathing
- Shortness of breath
- Blue tinge to lips and nail beds
- A rattling or crackling sound from the lungs (rales) when listened to through a stethoscope
In addition, other types of pneumonia may produce the following symptoms:
- Fatigue (sometimes lasting a long time after other symptoms disappear)
- Loss of appetite
Pneumonia is particularly difficult to spot in infants and children, who may not display prominent symptoms. Pneumonia could be suspected in infants and children who show the following symptoms:
- Rapid breathing
- Grunting sound
- Lack of appetite
- Abdominal pain
In both children and adults, a physician should be consulted if the symptoms of pneumonia are experienced. Some types of pneumonia can be fatal if left untreated.
The first step in diagnosing pneumonia is to consult a physician. A medical history will likely be taken. A physician will ask questions about symptoms and whether the patient has any history of similar illnesses. A physical examination may also be conducted and the physician may use a stethoscope to listen to the lung sounds. A crackling sound (rales) is usually an indication that there is fluid in the lungs and the patient may have pneumonia.
Other tests may be conducted, including:
- Chest x-ray. The chest x-ray is one of the most accurate methods of diagnosing pneumonia. In people with pneumonia, a shadow can sometimes be seen over the lungs. In some cases, the x-ray may not show signs of pneumonia, even though the patient is displaying clear symptoms. This may happen if the infection is in its early stages or it is affecting a part of the lung that is not easily seen by the x-ray. The physician may then recommend a CT (computed tomography) scan of the chest to develop a more accurate picture.
- Sputum culture. A physician may send out a sample of sputum or mucus (the discolored phlegm produced while coughing) to a laboratory to test it for signs of pneumonia germs. These tests are also used to indicate which medications the germs may respond to.
- Blood tests. In some cases, a complete blood count (CBC) may be conducted to count the number of white blood cells present in the blood. A high number of white blood cells normally means that the body is trying to fight an infection. However, this may not be the case for people with weakened immune systems. Other blood tests may be able to test for other microorganisms in the blood or whether the patient has bacteremia (bacteria in the blood), which is a common complication of some types of pneumonia.
- Blood oxygen measurement. Pneumonia can affect the absorption rate of oxygen into the bloodstream. To determine if this is occurring to a patient suspected of having pneumonia, a physician may attach a small infrared clip to the finger or the ear. This painlessly measures the amount of oxygen in the blood.
Treatment of pneumonia depends on which type of pneumonia is present. For bacterial pneumonia, antibiotics can be prescribed and are almost always effective in clearing the infection. Antibiotics are not effective against viral pneumonia or some other types of pneumonia. In these cases, the infection usually clears without medication.
An essential element of treatment for all types of pneumonia involves the care the patient should receive at home. This includes:
- Getting adequate rest.
- Drinking plenty of fluids.
- Taking over-the-counter medication to help fever. However, aspirin should never be provided to children due to the risk of the rare, but potentially fatal, Reye’s syndrome.
- Taking mild cough suppressants. It is important not to completely suppress the cough because coughing helps the lungs clear infected matter.
- Finishing all prescribed medication.
Depending on the type of pneumonia it may take several weeks to recover fully, although some symptoms may start to disappear after a few days of treatment. With certain strains of pneumonia, such as mycoplasma pneumonia, the patient may experience fatigue long after other symptoms cease.
Healthy adults with pneumonia are rarely hospitalized because home treatment for pneumonia is usually simple and effective. However, children and older adults, as well as those with complications arising from pneumonia, are sometimes admitted to the hospital for treatment. While hospitalized, patients may be administered oxygen therapy and antibiotics through an intravenous (I.V.) drip. The period of hospitalization varies.
Sometimes, complications arise from pneumonia that must be treated separately. For example, fluid may collect around the outside of the lungs (called pleural effusion), which a physician may have to extract by inserting a syringe into the chest cavity. Bacteremia occurs when the bacteria from pneumonia enters the bloodstream. It is a serious condition but can usually be treated with antibiotics.
One of the most effective ways to prevent transmission of the viruses and bacteria that can cause pneumonia is by practicing good hygiene. This includes washing hands after coughing or sneezing, or after coming into contact with a person with an infection. It is also important to cover the nose and mouth when sneezing or coughing. The spread of a virus can also be prevented by not sharing items such as towels, eating utensils, bottles or beverage containers with others. Tissues should be promptly disposed of after use, and hands should be washed after handling used tissues.
There are pneumonia vaccines available to people in high risk groups such as children, older adults and people with HIV, AIDS or other conditions that may affect the immune system. These include:
- Pneumococcal vaccine. This protects against the bacteria Streptococcus pneumoniae, which accounts for many cases of pneumonia in the United States. Although this type of pneumonia is bacterial and can be treated with antibiotics, it is developing antibiotic resistance because it is so common. The U.S. Centers for Disease Control and Prevention (CDC) recommends that people in the following groups receive the pneumococcal vaccine:
- People over 65.
- Children over 2 years old who are at a high risk for pneumonia.
- People with long-term serious health problems such as cardiovascular disease, sickle cell anemia, alcoholism, asthma or diabetes.
- People with HIV, AIDS or other conditions that impairs the immune system.
For children under 2 years old, there is a modified version of the pneumococcal vaccine available called the pneumococcal conjugate vaccine.
- Influenza (flu) vaccine. Because many strains of pneumonia are caused by a flu virus, having a flu shot every year can reduce the chances of contracting pneumonia. The flu shot must be given yearly because the flu virus constantly develops new strains. It is recommended for the following people:
- Infants between 6 months and 2 years old
- Adults older than 50
- People in high risk groups
There are no vaccines available that can protect against all types of pneumonia. Research has shown that those who practice prevention techniques, including receiving a flu shot, are less likely to contract pneumonia and may have shorter and milder bouts of pneumonia if it does occur. People with HIV, AIDS or those in other high-risk groups are encouraged to talk with their physician about additional ways to prevent pneumonia.
The following steps can also be taken to reduce the risk of pneumonia:
- Stop smoking.
- Avoid contact with anyone who has a viral or bacterial infection, especially the flu.
- Vaccinate children against common childhood illnesses which may cause pneumonia such as measles and chickenpox.
Patients may wish to ask their doctor the following questions related to pneumonia:
- Am I at risk for pneumonia?
- Is my child at risk for pneumonia?
- How can I tell if my influenza has turned into pneumonia?
- Could my pneumonia be caused by a more serious health condition?
- Will antibiotics be effective against my pneumonia?
- How long will it take me to recover from pneumonia? At what point will I no longer be contagious to others?
- Are there any over-the-counter medications I can take to ease my symptoms?
- Should I use a cough suppressant?
- Will my pneumonia interfere with my pregnancy?
- Should I be vaccinated against pneumonia?