Pneumonia is an inflammation of the lung caused by infection with bacteria, viruses, and other organisms. Pneumonia is usually triggered when a patient's defense system is weakened, most often by a simple viral upper respiratory tract infection or a case of influenza. Such infections or other triggers do not cause pneumonia directly but they alter the mucous blanket, thus encouraging bacterial growth. Other factors can also make specific people susceptible to bacterial growth and pneumonia.

Defining Pneumonia by Locations in the Lung

Pneumonia is sometimes defined in one of two ways according to its distribution in the lung:

Lobar Pneumonia (occurs in one lobe of the lung).

Bronchopneumonia (tends to be patchy).

Defining Pneumonia by Origin of Infection

Pneumonia is often classified into two categories that may help predict the organisms that are the most likely culprits.

Community-acquired (pneumonia contracted outside the hospital). Pneumonia in this setting often follows a viral respiratory infection. It affects nearly 4 million adults each year. It is likely to be caused by Streptococcus pneumoniae, the most common pneumonia-causing bacteria. Other organisms, such as atypical bacteria called Chlamydia or Mycoplasma pneumonia are also common causes of community-acquired pneumonia.

Hospital-acquired pneumonia. Pneumonia that is contracted within the hospital is called nosocomial pneumonia. Hospital patients are particularly vulnerable to gram-negative bacteria and staphylococci, which can be very dangerous.

Disease Process Leading to Pneumonia

Infectious agents reach the lungs and cause pneumonia through different routes:

Most often, organisms that cause pneumonia enter the lungs after being inhaled into the airways.

Sometimes the normally harmless bacteria present in the mouth may be aspirated into the lungs, usually if the gag reflex is suppressed.

Pneumonia may also be caused from infections that spread to the lungs through the bloodstream from other organs.

Under normal circumstances, however, the airways that take air in and pass through the upper part of the body have very effective mechanisms that protect the lung from infection by bacteria and other microbes.

Large particles are first filtered out in the nasal passage.

When smaller particles are inhaled, sensors along the airways trigger coughing or sneezing reflexes, which force many particles to back out.

Tiny ones that are able to reach the bronchioles are trapped in a mucous blanket and are then moved up and out of the lungs by the beating movements of tiny hair-like cells called cilia, a mechanism known as the mucociliary escalator.

Bacteria or other infectious agents that evade the airway defense system are attacked in the alveolar sacs by defenders from the body's immune system, particularly macrophages, large white blood cells that literally eat foreign particles.

These strong defense systems normally keep the lung sterile. If these defenses are weakened or damaged, however, bacteria or other organisms, such as viruses, fungi, and parasites, can gain the upper hand, producing pneumonia.

What Causes Pneumonia?

Bacteria are the most common causes of pneumonia, but these infections can also be caused by other microbial organisms. It is often impossible to identify the specific culprit Bacteria.

Many bacteria are categorized by the staining procedure used to visualize bacteria under a microscope. The stains determine if they are gram-negative or gram-positive bacteria. This gives the physician an idea of the severity of the pneumonia and how to treat it.

Gram-Positive Bacteria. These bacteria appear blue on the stain. The following are common gram-positive bacteria:

The most common cause of pneumonia is the gram-positive bacterium Streptococcus pneumoniae (also called S. pneumoniae or pneumococcal pneumonia). It was thought to cause 95% of community-acquired bacterial infection, but research now indicates it is far less, accounting for about half of all cases. (Some studies suggest it may account for even fewer, 10% to 30% of cases.)

Staphylococcus aureus, the other major gram-positive bacterium responsible for pneumonia, accounts for about 10% of bacterial cases. It is one of the main causes of pneumonia that occurs in the hospital (nosocomial pneumonia). It is uncommon in healthy adults but can develop about five days after viral influenza, usually in susceptible individuals, such as people with weakened immune systems, very young children, hospitalized patients, and drug abusers who use needles.

Streptococcus pyogenes or Group A Streptococcus.

Gram-Negative Bacteria. These bacteria stain pink . Gram negative bacteria are common infectious agents in hospitalized or nursing home patients, children with cystic fibrosis, and people with chronic lung conditions.

The most common gram-negative species causing pneumonia is Haemophilus influenzae (generally occurring in patients with chronic lung disease, older patients, and alcoholics).

Klebsiella pneumoniae may be responsible for pneumonia in alcoholics and in other people who are physically debilitated.

Pseudomonas aeruginosa is a major cause of pneumonia that occurs in the hospital (nosocomial pneumonia). It is common in pneumonia patients with chronic or severe lung disease.

Moraxella catarrhalis is found in everyone's nasal and oral passages. Experts have identified this bacteria as a cause of certain pneumonias, particularly in people with lung problems, such as asthma or emphysema.

Neisseria meningitidis is one of the most common causes of meningitis (central nervous system infection), but the organism has been reported in pneumonia, particularly in epidemics of military recruits.

Other gram-negative bacteria that cause pneumonia include E. coli (a cause in newborns), Proteus (found in several damaged lung tissue), and Enterobacter.

Atypical Pneumonia

Atypical pneumonias are generally caused by tiny nonbacterial organisms called Mycoplasma or Chlamydia pneumoniae and produce mild symptoms with a dry cough. Hospitalization is uncommon with pneumonia from these organisms.

Mycoplasma pneumoniae ( M. pneumoniae ) is the most common nonbacterial pneumonia. Mycoplasma is a very small organism that lacks a cell wall. It spreads from prolonged, close contact and is most often found in school-aged children and young adults. The condition is usually mild and is commonly known as walking pneumonia. Estimates of its prevalence in community acquired pneumonias in adults range from 1.9% to 30%. In one study, it accounted for over a third of pneumonia cases in children.

Another small non-bacterial organism, Chlamydia pneumoniae ( C. pneumoniae ), is now thought to cause 10% of all community-acquired cases of pneumonia. It is most common in young adults and children, where it is usually mild. In one study, it was the cause of 14% of cases in a group of children with pneumonia. While less common in the elderly, it can be very severe in this population.

Legionnaire's disease, first diagnosed in 1976, is caused by the organism Legionella pneumophila, and is acquired by breathing droplets of contaminated water. Outbreaks have most often been reported in hotels, cruise ships, and office buildings where people are exposed to contaminated droplets from cooling towers and evaporative condensers.

They have also been reported after exposure to whirlpools and saunas. Legionella is not passed on from person to person, but it may be much more common than once thought. Some experts even believe it causes 29% to 47% of all pneumonia cases. ( Legionella is sometimes categorized as an atypical pneumonia.)


Viruses that can cause or lead to pneumonia include influenza, respiratory syncytial virus (RSV), herpes simplex virus, varicella-zoster (the cause of chicken pox), and adenovirus. Outbreaks usually occur between January and April.

Influenza is associated with pneumonia directly or by altering the mucous blanket and making a person susceptible to bacterial pneumonia.

Respiratory syncytial virus (RSV) is a major cause of pneumonia in infants and people with damaged immune systems. Studies indicate that RSV pneumonia may also be more common than previously thought in adults, especially the elderly.

Adenoviruses have been implicated in about 10% of childhood pneumonia.

In adults, herpes simplex virus, adenoviruses, and varicella-zoster (the cause of chicken pox) are generally causes of pneumonia only in people with impaired immune systems.

Aspiration Pneumonia and Anaerobic Bacteria

The mouth harbors a mixture of bacteria that is harmless in its normal location but can cause a serious condition called aspiration pneumonia if it reaches the lung. This can happen during periods of altered consciousness, often when a patient is affected by drugs or alcohol, or after head injury or anesthesia. In such cases, the gag reflex is diminished, allowing these bacteria to enter the airways to the lung. These organisms are generally different from the usual microbes that enter the lung by inhalation. Many are often anaerobic (meaning they can live in the absence of oxygen).

Opportunistic Pneumonia

Impaired immunity leaves patients vulnerable to serious, even life-threatening, pneumonias known as opportunistic pneumonias. They are caused by microbes that are harmless to people with healthy immune systems. Infecting organisms include the following:

Pneumocystis carinii, an atypical organism that is very common and generally harmless in people with healthy immune systems.

Fungi, such as Mycobacterium avium.

Viruses, such as cytomegalovirus (CMV). AIDS is a major risk factor for opportunistic pneumonia, as are other conditions including lymphomas, leukemias, and other cancers. Long-term use of corticosteroids and other medications that suppress the immune system increase the susceptibility to these pneumonias.

Occupational and Regional Pneumonias

A number of people are exposed to pneumonia-causing organisms specific to particular occupations or regions.

Workers exposed to cattle, pigs, sheep, and horses are at risk for pneumonia caused by anthrax, brucellosis, and Q fever.

Agricultural and construction workers in the Southwest are at risk for coccidioidomycosis, and those working in Ohio and the Mississippi Valley are at risk for histoplasmosis.

Workers exposed to pigeons, parrots, parakeets, and turkeys are at risk for psittacosis.

Exposure to chemicals can also cause inflammation and pneumonia.

Hantavirus causes a dangerous form of lung disease and is carried by rodents, but is still rare. It does not appear to be contagious; cases have occurred in New Mexico, Arizona, California, Washington, and Mexico.

People in the southwest are also exposed to the fungus Coccidioides immitis , the cause of Valley fever, which is a lung infection that can cause pneumonia in susceptibl e indivi duals.

What are the Symptoms of Pneumonia?

Symptoms of Common Pneumonias

General Symptoms

The symptoms of bacterial pneumonia develop abruptly and may include chest pain, fever, shaking, chills, shortness of breath, and rapid breathing and heart beat.

Symptoms of pneumonia indicating a medical emergency include high fever, a rapid heart rate, low blood pressure, bluish-skin, and mental confusion.

Coughing up sputum containing pus or blood is an indication of serious infection.

Severe abdominal pain may accompany pneumonia occurring in the lower lobes of the lung.

In advanced cases, the patient's skin may become bluish (cyanotic), breathing may become labored and heavy, and the patient may become confused.

Symptoms in the Elderly. It is important to note that older people may have fewer or different symptoms than younger people have. An elderly person who experiences even a minor cough and weakness for more than a day should seek medical help. Some may exhibit confusion, lethargy, and general deterioration.

Symptoms of Pneumonia Causes by Anaerobic Bacteria

People with pneumonia caused by anaerobic bacteria such as Bacteroides, which can produce abscesses, often have prolonged fever and productive cough, frequently showing blood in the sputum, which indicates necrosis (tissue death) in the lung. About a third of these patients experience weight loss.

Symptoms of Atypical Pneumonia

General Symptoms for Atypical Pneumonias. Atypical nonbacterial pneumonia is most commonly caused by Mycoplasma and usually appears in children and young adults.

Symptoms progress gradually, often beginning with general flu-like symptoms, such as fatigue, fever, weakness, headache, nasal discharge, sore throat, ear ache, and stomach and intestinal distress.

Vague pain under and around the breast bone may occur, but the severe chest pain associated with typical bacterial pneumonia is uncommon.

Patients may experience a severe hacking cough, but it usually does not produce sputum.

Symptoms of Legionnaire's Disease. Symptoms of Legionnaire's disease usually evolve more rapidly and include high fever, a dry cough, and shortness of breath, often accompanied by headache, muscle pains, fatigue, gastrointestinal problems, and mental confusion.

How Serious is Pneumonia?

General Outlook

About 1.2 million people are hospitalized each year for pneumonia, which is the third most frequent reason for hospitalizations (births are first and heart disease is second). Although the majority of pneumonias respond well to treatment, the infection can still be a very serious problem. Together with influenza, pneumonia is the sixth leading cause of death in the US and is the leading cause of death from infection. Outlook for High-Risk Individuals

Severity varies widely depending on individual factors, including the following:

Hospitalized Patients. For patients who require hospitalization for pneumonia, the mortality rate is between 10% and 25%. If pneumonia develops in patients already hospitalized for other conditions, the mortality rates are higher. They range from 50% to 70% and are greater in women than in men.

Older Adults. The elderly have lower survival rates, particularly those with other medical problems. (Even when older individuals recover from community-acquired pneumonia, they have higher than normal mortality rates over the next several years.)

Very Young Children. About 20% of stillborn and very early infant mortality deaths are due to pneumonia. Small children who develop pneumonia are at risk for developing lung problems in adulthood.

Pregnant Women. Pneumonia poses a special hazard for pregnant women.

Patients with Impaired Immune Systems. Pneumonia is particularly serious in people with impaired immune systems, particularly AIDS patients, in whom pneumonia causes about half of all deaths.

Patients with Serious Medical Conditions. The disease is also very dangerous in people with diabetes, cirrhosis, sickle cell anemia, multiple myeloma, and in those who have had their spleens removed.

Risk by Organisms:

Lower-Risk Organisms. The following organisms usually cause pneumonias that are responsive to treatment or mild.

S. Pneumonia is the most common organism and, although it can cause severe pneumonia, it is very responsive to many antibiotics.

Mycoplasma and Chlamydia are common causes of pneumonia in children and young adults. They are generally mild and rarely require hospitalization when they are appropriately treated, although recovery may still be prolonged. Severe and life-threatening cases are more likely to occur in elderly people with other medication conditions.

High-Risk Organisms. The following are high-risk infecting organisms that pose a particular risk for dangerous pneumonia:

High-risk gram positive bacteria. Staphylococcus aureus. Poses a higher risk for multiple small abscesses in the lung and necrosis (tissue death).

High-risk gram-negative bacteria include the following:

Pseudomonas aeruginosa.

Klebsiella pneumonia. Poses a risk for abscesses and severe lung tissue damage.

Legionella pneumophila. Particularly virulent and can cause damage throughout the body.

Viral pneumonia is usually very mild but there are exceptions.

Influenza pneumonia can be very serious.

Respiratory syncytial virus (RSV) pneumonia rarely poses a danger for healthy young adults. However, between 22,000 and 44,500 children are hospitalized each year because of pneumonia from RSV and the incidence seems to be increasing. Between 2% to 9% of hospitalized pneumonia cases in the elderly may be due to respiratory syncytial virus.

Complications of Pneumonia

Abscesses. Abscesses in the lung are thick-walled, pus-filled cavities that are formed when infection has destroyed lung tissue. They are frequently a result of aspiration pneumonia, when a mixture of organisms is carried into the lung. Abscesses can cause hemorrhage in the lung if untreated, but antibiotics that target specific anaerobic bacteria and other organisms have significantly reduced their danger. Abscesses are more common with Staphylococcus aureus or Klebsiella pneumoniae , and uncommon with Streptococcus pneumoniae .

Respiratory Failure. Respiratory failure is one of the most important causes of death in patients with pneumococcal pneumonia. Acute respiratory distress syndrome (ARDS) is the specific condition that occurs when the lungs are unable to function and oxygen is so severely reduced that the patient's life is at risk. Failure can occur from mechanical changes in the lungs caused by the pneumonia (called ventilatory failure) or from loss of oxygen in the arteries when pneumonia results in abnormal blood flow (called hypoxemic respiratory failure).

Bacteremia. Bacteremia (bacteria in the blood) is the most common complication of Streptococcus pneumoniae, but rarely does this infection spread to other sites. Bacteremia is also a frequent complication of other gram-negative organisms, including Haemophilus influenzae.

Pleural Effusions and Empyema. The pleura are two thin membranes:

The visceral pleura covers the lungs.

The parietal pleura covers the chest wall.

The narrow zone between these two pleural membranes normally contains a tiny amount of fluid that helps lubricate the lung. In about 20% of patients who are hospitalized for pneumonia, this fluid builds up around the lung.

In most cases, particularly in Streptococcus pneumoniae, the fluid remains sterile, but occasionally it can become infected and even filled with pus (a condition called empyema). Empyema sometimes occurs with Staphylococcus aureus or Klebsiella pneumoniae. The condition can cause permanent scarring. Pneumonia may also cause the pleura to become inflamed, which can result in breathlessness and acute pain.

Collapsed Lung. Air may fill up the area between the pleural membranes causing pneumothorax, or collapsed lung. The condition can be a complication of pneumonia (particularly pneumococcal pneumonia) or of some of the invasive procedures used to treat pleural effusion.

Other Complications of Pneumonia. In rare cases, infection may spread from the lungs to the heart and can even spread throughout the body, sometimes causing abscesses in the brain and other organs. Severe hemoptysis (coughing up blood) is another potentially serious complication of pneumonia, particularly in patients with other lung problems such as cystic fibrosis.

Long Term Effects of Atypical Pneumonias

Both Mycoplasma and Chlamydia pneumonias, the primary atypical pneumonias, are usually mild. Some research is suggesting, however, that they may have certain adverse long-term effects even in healthy younger individuals.

Heart Disease and Stroke. Research has suggested that the Chlamydia (C.) pneumoniae may trigger an immune response that causes inflammation and damage over time in the arteries or heart muscle. In a 2000 study, C. pneumoniae was associated with a thickening in the carotid artery which leads to the brain. Nevertheless, studies on a causal relationship between C. pneumonia and heart disease or stroke have been mixed. The most recent ones have found no strong association between the infection and heart disease while others downstate a possible link.

Neurologic Diseases. Some research suggests that C. pneumonia may affect the brain.

Researchers have also detected C. pneumoniae in areas of the brain affected by Alzheimer's but not in other areas, suggesting that the inflammatory response may contribute to this dreaded disease.

Another study reported an association between Chlamydia and multiple sclerosis, another neurologic disease caused by the inflammatory process.

Asthma. Chlamydia pneumoniae, Mycoplasma pneumoniae, and the respiratory syncytial virus are becoming important suspects in many cases of severe adult asthma. (Serious respiratory infections that occur in early childhood, however, probably do not play a role in asthma that develops in adulthood.)

Who Gets Pneumonia?

General Risk Factors for Community-Acquired Pneumonia

Community-acquired pneumonia is the most common type and develops outside of the hospital. Each year between two and four million people in the US develop community-acquired pneumonia, and 600,000 people are hospitalized because of it. The elderly (who have diminished cough and gag reflexes and faltering immune systems), infants, and young children (who have immature immune systems and narrow airways) are at greater risk for pneumonia than are young and middle-aged adults. In the US the incidence is higher in African-Americans than in Caucasians.

General Risk Factors for Hospital-Acquired (Nosocomial) Pneumonia

Aside from specific conditions that predispose one to pneumonia, people who are hospitalized have a higher risk for pneumonia than those who are not.

Pneumonia that is contracted in the hospital is called nosocomial pneumonia and affects an estimated five to 10 out of every 1000 hospitalized patients every year. The following conditions put hospitalized people at higher risk:

Surgery, particularly splenectomy or operations that impair coughing.

Being in the intensive care unit on mechanical ventilators. Ventilated patients who lie flat on their backs are at particular risk for aspiration pneumonia; raising the patient up may reduce this risk.

Hospitalized patients are particularly vulnerable to gram-negative bacteria and staphylococci, which can be very dangerous, particularly in people who are already ill

Risk Factors in Adults

Dormitory or Barrack Conditions. Recruits on military bases and college students are at higher than average risk for Mycoplasma pneumonia , which is usually mild. These groups are at lower risk, however, for more serious types of pneumonia.

Smoke and Environmental Pollutants. The risk for pneumonia in smokers of more than a pack a day is three times that of nonsmokers. Those who are chronically exposed to cigarette smoke, which can injure airways and damage the cilia, are also at risk. Quitting smoking reduces the risk of dying from pneumonia to normal, but the full benefit takes ten years to be realized. Toxic fumes, industrial smoke, and other air pollutants may also damage cilia function.

Drugs and Alcohol. Alcohol or drug abuse is strongly associated with pneumonia. These substances act as sedatives and can diminish the reflexes that trigger coughing and sneezing. Alcohol also interferes with the actions of macrophages, the white blood cells that destroy bacteria and other microbes. Intravenous drug abusers are at risk for pneumonia from infections that originate at the injection site and spread through the blood stream.

Compromised Immune Systems

People with impaired immune systems are extremely susceptible to pneumonia. In addition to AIDS, other conditions that compromise the immune system include organ transplantation, chemotherapy, and cancers, especially leukemia and Hodgkin's disease. Patients who are on corticosteroid or other medications that suppress the immune system are also prone to infection.

Chronic Lung Disease

Chronic obstructive lung diseases, including chronic bronchitis and emphysema, are major risk factors for pneumonia.

Specific Risk Factors for Recurrent Pneumonia in Children

Certain children have a higher than normal risk for pneumonia and its recurrence. Conditions that predispose infants and small children to pneumonia include the following:

Impaired immune system.

Gastroesophageal reflux disorder.

Inborn lung or heart defects.

Abnormalities in muscle coordination in the mouth and throat.


Certain genetic disorders. They include sickle-cell disease, cystic fibrosis (which causes mucus abnormalities), and Kartagener's syndrome (which results in malfunctioning cilia, the hair-like cells lining the airways).

How is Pneumonia Diagnosed?

In many cases of mild-to-moderate community-acquired pneumonia, the physician is able to diagnose and treat pneumonia based solely on a history and physical examination. Often, however, a diagnosis is not straightforward, particularly in hospitalized patients.

Physical Examination

Use of the Stethoscope. The most important diagnostic tool for pneumonia is the stethoscope. Sounds in the chest that may indicate pneumonia are the following:

Rales (a bubbling or crackling sound). Rales on one side of the chest and rales heard while the patient is lying down is strongly suggestive of pneumonia.

Rhonchi (abnormal rumblings indicating the presence of thick fluid).

Percussion. The physician will also use a test called percussion, in which he or she taps the chest lightly. A dull thud instead of a healthy hollow-drum-like sound, indicates certain condition that suggest pneumonia, including the following:

Consolidation (a condition, in which the lung becomes firm and inelastic).

Pleural effusion (fluid build-up in the space between the lungs and the lining around it).

Diagnostic Difficulties in Hospitalized Patients

Diagnosing pneumonia is particularly difficult in hospitalized patients (called nosocomial pneumonia) for a number of reasons, including the following:

Many hospitalized patients have similar symptoms, including fever or signs of lung infiltration on x-rays.

In hospitalized patients, sputum or blood tests often indicate the presence of bacteria or other organisms, but such agents do not necessarily indicate pneumonia.

For a diagnosis of nosocomial pneumonia, physicians should be sure to rule out other conditions, using a chest x-ray, two sets of blood cultures, a urine analysis for Legionella, lung fluid sample, and possibly other tests for specific organisms.

Laboratory Tests for Diagnosing Infection and Identifying Bacterial Agents

Although antibiotics are available that can destroy a wide spectrum of organisms, it would be preferable to use an antibiotic that can target the specific microorganism causing the pneumonia. Researchers, then, are looking for laboratory tests that would identify the specific organism or virus causing the pneumonia. Unfortunately, people harbor many bacteria, and sputum and blood tests are not always effective in distinguishing between harmless and harmful microscopic agents. In severe cases, physicians particularly need to use invasive diagnostic measures to identify the infecting agent.

Urine Tests. A urine test (NOW) is up to 93% accurate in identifying S. pneumoniae within 15 minutes. However, a 2000 study indicated that it is not likely to be useful in diagnosing S. pneumoniae as a cause of pneumonia in children, since the organism is very common in the noses and throats of children. This organism, then, would very likely be picked up by the test even if it were not the cause of the pneumonia.

Sputum Tests. Only a sample of sputum coughed from the lungs will yield the infecting organism, and, even then, tests are not always successful in revealing the culprit. The following steps may be required:

The physician first asks the patient to cough as deeply as possible to produce an adequate sputum sample. A shallow cough produces a sample that usually only contains normal mouth bacteria.

A patient who is not able to cough sufficiently may be asked to inhale a saline spray that helps produce an adequate sputum sample.

In some cases, a tube will be inserted through the nose down into the lower respiratory tract to induce a deeper cough.

Even before sending the sample to the laboratory, the physician will check it for the following:

Presence of blood (an indication of infection).

Color and consistency. If the sputum is opaque and colored yellow, green, or brown, then infection is likely. Clear, white, glistening sputum indicates no infection.

In the laboratory, the sputum sample may be used as follows:

A Gram's stain is made, which may reveal the presence of bacteria and whether they are gram-negative or positive.

A sputum culture may be performed, in which organisms are grown in the laboratory.

Blood Tests. Blood tests may be used for the following:

White blood cell count. High levels indicate infection.

Blood cultures. They may be performed for detecting the specific organism causing the pneumonia, but are not often helpful in distinguishing harmful from harmless organisms. They are accurate in only 10% to 30% of cases, and their use should generally be limited to severe cases.

Detection of antibodies to S. pneumoniae. Researchers are using specialized techniques to detect antibodies to S. pneumoniae (immune factors that target specific foreign invaders), but it is not clear if they are accurate.

Laboratory Tests for Less Common Organisms

If uncommon organisms, such as Legionella, Mycoplasma, and Chlamydia organisms, are strongly suspected more advanced laboratory tests may be used:

Specialized techniques can detect antibodies to the organisms in blood samples, but these antibodies, such as those responding to Mycoplasma or Chlamydia , are not present early enough in the course of pneumonia to permit prompt diagnosis and treatment.

A test performed on whole blood samples that uses a technique called polymerase chain reaction (PCR) is useful for identifying certain atypical strains, including Mycoplasma and Chlamydia pneumoniae, but it is expensive.

A urine test can be used to diagnose some cases of Legionnaire's disease.

DNA probes are being developed to detect these organisms in respiratory secretions.

In addition, special stains and cultures are required to detect tuberculosis and fungal infections.

Chest X-Rays and Other Imaging Techniques

X-Rays. A chest x-ray is nearly always taken to confirm a diagnosis of pneumonia. It may reveal the following:

White areas in the lung called infiltrates, which indicate infection.

Complications of pneumonia, including pleural effusions (fluid around the lungs) and abscesses.

Other Imaging Tests. Computed tomography (CT) scans or MRIs may be obtained in the following circumstances:

If x-ray results are unclear.

When patients do not respond to antibiotics.

When patients have complications.

When patients have other serious health problems.

These more sophisticated imaging techniques can help detect the presence of tissue damage, abscesses, and enlarged lymph nodes. They can also detect some tumors that block bronchial tubes. No imaging technique can determine the actual organism causing the infection.

Invasive Diagnostic Procedures

Invasive diagnostic procedures may be required in the following circumstances:

When patients have life-threatening complications.

When patients have failed standard treatments for no known reason.

When AIDS or other immune problems are present.

Each of the procedures has potential complications and is not used under ordinary conditions.

Thoracentesis. If a physician detects pleural effusion and suspects that empyema (pus) is present, thoracentesis is performed:

Fluid in the pleura is withdrawn using a long thin needle inserted between the ribs.

The fluid is then tested using blood cell counts, Gram stains, cultures, and chemical tests.

Complications of this procedure include collapsed lung, bleeding, and introduction of infection.

Bronchoscopy. A bronchoscopy employs the following:

The patient is given a local anesthetic, supplementary oxygen, and sedatives.

The physician inserts a fiberoptic tube into the lower respiratory tract through the nose or mouth.

The tube acts like a telescope into the body, allowing the physician to view the wind-pipe and major airways for pus, abnormal mucus, or other problems.

The doctor removes specimens for analysis and can also treat the patient by remov

Chest Therapy

Chest therapy using incentive spirometry, rhythmic inhalation and coughing, and chest tapping are all important techniques to loosen the mucus and move it up out of the lungs. It should be used both in the hospital and when the patient returns home during recovery.

Incentive Spirometry. The patient uses an incentive spirometer at regular intervals.

The spirometer is a hand-held clear plastic device that includes a breathing tube and a container with a movable gauge.

The patient first exhales through the tube.

Then the patient inhales as strongly as possible.

The force of the inhalation raises a gauge inside the device to the highest level possible.

This practice helps the patient exercise the lungs. The height of the gauge at inhalation also helps the health professional to determine the state of the patient's lung function.

Rhythmic Breathing and Coughing. During recovery, the patient performs rhythmic breathing and coughing every four hours:

Before starting the breathing exercise, the patient should tap lightly on the chest to loosen mucus within the lung. If available, a caregiver should also tap on the patient's back.

The patient inhales rhythmically and deeply three or four times.

The patient then coughs as deeply as possible with the goal of producing sputum.

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