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Pneumonia is an inflammation of the lung caused by infection with bacteria, viruses, or other organisms. Pneumonia is
usually triggered when a person's defense system is weakened, most often by a simple viral upper respiratory tract
infection or a case of influenza (the flu). Such infections or other triggers do not cause pneumonia directly, but they
alter the protective blanket of mucous in the lungs (which prevents foreign substances from getting into the lungs), thus
encouraging bacterial growth. Other factors can also make specific people susceptible to bacterial growth in the lungs
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 or part of the lung).

Bronchopneumonia (tends to be patchy and occurs throughout the lung).

[For a description of the lung, see Box The Lungs.]
Defining Pneumonia by Origin of Infection
Pneumonia is often classified into two categories according to where the patient contracted it, which helps predict the
organisms that are the most likely culprits.
Community?Acquired Pneumonia (CAP). People with community?acquired pneumonia have contracted it outside a
hospital setting. It is very common and affects nearly four million adults each year. CAP often follows a viral
respiratory infection, such as influenza. It is likely to be directly caused, however, 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 CAP.
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 (which usually keeps substances out of the lung) is suppressed.
Pneumonia may also be caused from infections that spread to the lungs through the bloodstream from other

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 particles that are able to reach the bronchioles are trapped in a mucous blanket. They 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, which are 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.
The Lungs
The lungs are two spongy organs in the chest surrounded by a thin, moist membrane called the pleura. They are
the largest organs in our body. Each lung is composed of smooth, shiny lobes; the right lung has three lobes and
the left has two. Approximately 90% of the lung is filled with air and only 10% is solid tissue. When a person
inhales, the air travels through the following structures:
Air is carried from the trachea (the windpipe) into the lung through flexible airways called bronchi.

Like the branches of a tree, bronchi divide successively into over a million smaller airways called bronchioles.
The bronchioles lead to grape?like clusters of microscopic sacs called alveoli. In each lung of an adult there are
millions of these tiny alveoli.
Each alveoli has a thin membrane through which oxygen and carbon dioxide pass to and from capillaries, the
smallest of our blood vessels. During deep inhalation, the alveoli unfold and expand to allow fresh oxygen to pass
into the capillaries and remove carbon dioxide waste to pass out of the body through the lungs.
The oxygen?rich blood is carried back through blood vessels to the heart, where it is pumped through the body.
Bacterial Pneumonias
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.
Many bacteria are categorized by the laboratory procedure used to visualize bacteria under a microscope. Bacteria are
stained to 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 since different bacteria are treated with different drugs.
Gram?Positive Bacteria. These bacteria appear blue on the stain and are the most common organisms found in
pneumonia. They include the following:
The most common cause of pneumonia is the gram?positive bacterium

Streptococcus pneumoniae (also called
S. pneumoniae or the pneumococcus). It accounts for about 20% to 60% all community?acquired bacterial
pneumonias (CAPs) in adults. Studies also suggest it causes between 13% to 38% of CAP in children.
Staphylococcus (S.) aureus

, the other major gram?positive bacterium responsible for pneumonia, accounts for
about 2% of community?acquired pneumonias and between 10% and 15% of hospital?originated pneumonias.
It is the organism most often associated with viral influenza, and can develop about five days after the onset of
flu symptoms. Pneumonia from S. aureus most often occurs in people with weakened immune systems, very
young children, hospitalized patients, and drug abusers who use needles. It is uncommon in healthy adults.
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.
Haemophilus (H.) influenzae

is the second most common organism causing community acquired pneumonia
and accounts for 3% to 10% of all cases (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. It is also associated with recent use of potent antibiotics.
Pseudomonas aeruginosa

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

is found in everyone's nose and mouth. Experts have identified this bacterium as an
uncommon cause of certain pneumonias, particularly in people with lung problems, such as asthma or
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 and also associated
with recent antibiotic use), Proteus (found in damaged lung tissue), and Enterobacter.
Atypical Pneumonia
Atypical pneumonias are generally caused by tiny nonbacterial organisms and produce mild symptoms with a dry
cough. Hospitalization is uncommon with pneumonia from these organisms, but there are exceptions. They include the
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.
Chlamydia pneumoniae

(C. pneumoniae) is now thought to cause 10% of all community?acquired cases of
pneumonia. This atypical pneumonia 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
Viral Pneumonia
A number of viruses can cause pneumonia either directly or indirectly, and include the following:
Influenza. Pneumonia is the major serious complication of viral influenza (the "flu") and can be very serious. It

can develop about five days after flu symptoms start. Influenza is associated with pneumonia directly or
indirectly by altering the mucous blanket and making a person susceptible to bacterial pneumonia.
Respiratory syncytial virus (RSV). Most infants are infected with RSV at some point, but it is most often mild.

Still, RSV is a major cause of pneumonia in infants and people with damaged immune systems. Some
evidence suggests that it may increase the risk for the development of asthma. Studies indicate that RSV
pneumonia may also be more common than previously thought in adults, especially the elderly. [See Box
Preventing and Treating Respiratory Syncytial Virus (RSV) Pneumonia in Children.]
Severe acute respiratory syndrome (SARS). SARS is a respiratory infection caused by a new coronavirus,

which appears to have jumped to humans from animals. It is a serious infection first identified in China that is
transmitted by close contact with an infected individual. [See Box Severe Acute Respiratory Syndrome
Human parainfluenza virus (HPV). HPV is second to RSV in causing pneumonia and bronchitis in children

and is also an important cause of pneumonia in the elderly and in patients with damaged immune systems.
Adenoviruses. Adenoviruses are common and ordinarily are not problematic, although they have been

implicated in about 10% of childhood pneumonia.
Herpesviruses. In adults, herpes simplex virus 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. It is the most common cause of pneumonia in AIDS patients.
Fungi, such as

Mycobacterium avium.
Viruses, such as cytomegalovirus (CMV).

In addition to AIDS patients, other conditions also put patients at risk for opportunistic pneumonia. They include
lymphomas, leukemias, and other cancers. Long?term use of corticosteroids and drugs known as immunosuppressants
increase the susceptibility to these pneumonias.
Occupational and Regional Pneumonias
Exposure to chemicals can also cause inflammation and pneumonia. A number of people are exposed to
pneumonia?causing organisms specific to particular occupations or regions.
Anthrax. Workers exposed to cattle, pigs, sheep, and horses are at risk for pneumonia caused by anthrax,

brucellosis, and Q fever. (Anthrax, of course, has become a major focus of concern because of its use in
terrorist attacks in the US.)
Coccidoidomycosis. Agricultural and construction workers in the Southwest are at risk for coccidoidomycosis,

and those working in Ohio and the Mississippi Valley are at risk for histoplasmosis.
Psittacosis. Workers exposed to pigeons, parrots, parakeets, and turkeys are at risk for psittacosis.


Hantavirus. 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
Coccidioides immitis

. 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 susceptible individuals.
Severe Acute Respiratory Syndrome (SARS)
Severe Acute Respiratory Syndrome (SARS) is a contagious respiratory infection that was first described on
February 26, 2003. It was first identified as a new disease by World Health Organization (WHO) physician Dr.
Carlo Urbani, who diagnosed it in a 48?year?old businessman who had traveled from the Guangdong province of
China, through Hong Kong, to Hanoi, Vietnam. The businessman died from the illness. Dr. Urbani subsequently
died from SARS on March 29, 2003 at the age of 46. In the meantime, SARS began to spread, and within 6
weeks of its discovery, it had infected thousands of people around the world, including people in Asia, Australia,
Europe, Africa, and North and South America. Schools had closed throughout Hong Kong and Singapore.
National economies were affected. The WHO had identified SARS as a global health threat, and issued an
unprecedented travel advisory. But it wasn't clear whether SARS would become a global pandemic, or would
settle into a less aggressive pattern.
SARS is a serious form of atypical pneumonia, resulting in acute respiratory distress and sometimes death. It is a
dramatic example of how quickly world travel can spread a disease. It is also an example of how quickly a
networked health system can respond to an emerging threat.
Causes And Risk Factors
SARS is a new member of the coronavirus family (the same family that can cause the common cold). The
discovery of these viral particles represents some of the fastest identification of a new organism in history.
SARS is clearly spread by droplet contact. When someone with SARS coughs or sneezes, infected droplets are
sprayed into the air. Like other coronaviruses, the SARS virus may live on hands, tissues, and other surfaces for
up to 6 hours in these droplets and up to 3 hours after the droplets have dried. (Also, with other coronaviruses,
re?infection is common.) While droplet transmission through close contact was responsible for most of the early
cases of SARS, evidence began to mount that SARS might also spread by hands and other objects the droplets
had touched. Airborne transmission was a real possibility in some cases. Live virus had even been found in the
stool of people with SARS, where it has been shown to live for up to four days. And the virus may be able to live
for months or years when the temperature is below freezing.
With other coronaviruses, re?infection is common. Preliminary reports suggest that this may also be the case with
Preliminary estimates are that the incubation period is usually between two and ten days, although there have
been documented cases where the onset of illness was considerably faster or slower. People with active symptoms
of illness are clearly contagious, but it is not known how long contagiousness may begin before symptoms appear
or how long contagiousness might linger after the symptoms have disappeared.
Reports of possible relapse in patients who have been treated and released from the hospital raise concerns about
the length of time individuals can harbor the virus.
Minimizing contact with people with SARS minimizes the risk of the disease. This might include minimizing
travel to locations where there is an uncontrolled outbreak. Where possible, direct contact with people with SARS
should be avoided until 10 days after the fever and other symptoms are gone.
The CDC has identified hand hygiene as the cornerstone of SARS prevention. This might include hand washing
or cleaning hands with an alcohol?based instant hand sanitizer.
People should be taught to cover the mouth and nose when sneezing or coughing. Respiratory secretions should
be considered to be infectious, which means no sharing of food, drink, or utensils. Commonly touched surfaces
can be cleaned with an EPA approved disinfectant.
In some situations, masks and goggles may be useful for preventing airborne or droplet spread. Gloves might be
used in handling potentially infectious secretions.

The hallmark symptoms are fever greater than 100.4 F (38.0 C) and cough, difficulty breathing, or other
respiratory symptoms. Symptoms found in more than half of the first 138 patients included (in the order of how
commonly they appeared):

chills and shaking

muscle aches



Less common symptoms include (also in order):

productive cough (sputum)

sore throat

runny nose

nausea and vomiting


Signs And Tests:
Listening to the chest with a stethoscope (auscultation) may reveal abnormal lung sounds. In most people with
SARS, progressive chest X?ray changes or chest CT changes demonstrate the presence of pneumonia.
Much attention was given early in the outbreak to developing a quick, sensitive test for SARS. Specific tests for
the SARS virus include the PCR for SARS virus, antibody tests to SARS (such as ELISA or IFA), and direct
SARS virus isolation. All current tests have some limitations. General tests used in the diagnosis of SARS might
a chest X?ray or chest CT

a CBC (people with SARS tend to have a low white blood cell count (leukopenia), a low lymphocyte

count (lymphopenia), and/or a low platelet count (thrombocytopenia)
clotting profiles (often prolonged clotting)

blood chemistries (LDH levels are often elevated. ALT and CPK are sometimes elevated. Sodium and

potassium are sometimes low.)
People suspected of having SARS should be evaluated immediately by a physician. Antibiotics are sometimes
given in an attempt to treat bacterial causes of atypical pneumonia. Antiviral medications have also been used.
High doses of steroids have been employed to reduce lung inflammation. In some serious cases, serum from
people who have already gotten well from SARS (convalescent serum) has been given. Evidence of general
benefit of these treatments has been inconclusive.
Other supportive care such as supplemental oxygen, chest physiotherapy, or mechanical ventilation is sometimes
As the first wave of SARS began to subside, the death rate proved to have been about 14 or 15 percent of those
diagnosed. In people over age 65 the death rate was higher than 50 percent. Many more were sick enough to
require mechanical ventilation. And more still were sick enough to require ICU care. Intensive public health
policies are proving to be effective in controlling outbreaks. Many nations have stopped the epidemic within their
own countries. All nations must be vigilant, however, to keep this disease under control. Viruses in the
coronavirus family are known for their ability to spawn new mutations in order to better spread among humans.
respiratory failure

liver failure

heart failure

myelodysplastic syndromes

Call Health Care Provider:
Call your health care provider if you suspect you or someone you have had close contact with has SARS.

Symptoms of Common Bacterial Pneumonias
General Symptoms. The symptoms of bacterial pneumonia develop abruptly and typically include the following:
A single episode of shaking chills followed by fever.

Chest pain on the side of lung infection. (Severe abdominal pain occurs in some people with pneumonia in the

lower lobes of the lung.)
Shortness of breath.

Rapid breathing and heart beat.

Cough. May be dry initially but it eventually produces more fluid (sputum).

Sometimes nausea, vomiting, muscle aches occurs.

Emergency Symptoms. Symptoms of pneumonia indicating a medical emergency include the following:
High fever.

A rapid heart rate.

Bluish?toned (cyanotic) skin.

Labored and heavy breathing.

Mental confusion.

Coughing up sputum containing pus or blood.

Symptoms in the Elderly. It is important to note that older people may have fewer or different symptoms than younger
people. Symptoms may come on much more slowly. 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
Symptoms of Pneumonia Caused by Anaerobic Bacteria
Pneumonia caused by anaerobic bacteria such as Bacteroides can produce dangerous abscesses in the lungs. People
with such pneumonias may have prolonged fever and productive cough, frequently showing blood in the sputum. Signs
of blood may indicate dead lung tissue (necrosis). 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 and may have the following course:
General flu?like symptoms are often the first indications. They may include fatigue, fever, weakness,

headache, nasal discharge, sore throat, earache, and stomach and intestinal distress.
Vague pain under and around the breastbone 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.
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. It kills between 40,000 and 70,000 people each year.
Together with influenza, pneumonia is the sixth leading cause of death in the US and is the leading cause of death from
Outlook for High?Risk Individuals
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. Community?acquired pneumonia is responsible for 350,000 to 620,000 hospitalizations in elderly people
every year. The elderly have lower survival rates than younger people, and pneumonia and influenza are the fifth
leading causes of death in this population. Even when older individuals recover from community?acquired pneumonia,
they have higher than normal mortality rates over the next several years. Elderly people at particular risk are those with
other medical problems and nursing home patients.
Very Young Children. About 20% of deaths in stillborn and very young infants are due to pneumonia. Small children
who develop pneumonia and survive are at also 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 disease, cancer, and in those who have had their spleens removed.
Risk by Organisms
Specific organisms vary in their effects. Mild pneumonia is usually associated with the atypical organisms Mycoplasma
and Chlamydia. Severe pneumonia is most often associated with a wide range of organisms. Some are very virulent
(potent) but are extremely curable, while others are difficult to treat.

and Chlamydia are the most common causes of mild pneumonias and are most likely to occur in
children and young adults. They 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.
S. Pneumonia

is the most common cause of pneumonia and, in fact, all upper respiratory infections. It can
produce severe pneumonia, with mortality rates of 10%. Nevertheless, it is very responsive to many
Staphylococcus aureus

is a gram?positive bacterium that often causes severe pneumonia in hospitalized
patients and following influenza A and B in high?risk patients. People who get this form of pneumonia may
develop pockets of infection in their lungs called abscesses that are difficult to treat and can cause death of
lung tissue, or necrosis. Mortality rates are high, 30% to 40%, in part because the patients who develop this
infection are generally very ill or vulnerable.
Pseudomonas aeruginosa

and Klebsiella pneumonia are gram?negative bacteria that pose a risk for abscesses
and severe lung tissue damage.
Legionella pneumophila

is very virulent and can cause widespread damage. Treatments have improved
dramatically since it was first identified. However, a 2002 suggested that many patients experience long?term
problems, including neurologic and muscular complications, coughing, shortness of breath, and fatigue.
Viral pneumonia is usually very mild, but there are exceptions. Pneumonia associated with influenza can be

serious. Respiratory syncytial virus (RSV) pneumonia rarely poses a danger for healthy young adults, but can
be life threatening in infants and serious in the elderly. The incidence seems to be increasing.
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 if a mixture of organisms is carried into the lung.
Abscesses can cause hemorrhage (bleeding) in the lung if untreated, but antibiotics that target them 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 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 if pneumonia leads to
mechanical changes in the lungs (called ventilatory failure) or oxygen loss in the arteries (called hypoxemic respiratory
Bacteremia. Bacteremia (bacteria in the blood) is the most common complication of pneumococcus infection, although
it rarely spread to others sites. Bacteremia is a frequent complication of infection from other gram?negative organisms,
including Haemophilus influenzae.
Pleural Effusions and Empyema. The pleura are two thin membranes:
The visceral pleura cover the lungs.

The parietal pleura cover the chest wall.


In some cases of pneumonia, the pleura become inflamed, which can result in breathlessness and acute chest pain when
Also, in about 20% of pneumonia cases there is build?up of the fluid between the pleural membranes that lubricates the
lung. (Ordinarily the narrow zone between the two membranes contains only a tiny amount of fluid.)
In most cases, particularly in Streptococcus pneumoniae, the fluid remains sterile (no bacteria are present), but
occasionally it can become infected and even filled with pus (a condition called empyema). Empyema is more likely to
occur with specific organisms, such as Staphylococcus aureus or Klebsiella pneumoniae infections. The condition can
cause permanent scarring.
Collapsed Lung. In some cases, air may fill up the area between the pleural membranes causing the lungs to collapse, a
condition called pneumothorax. It can be a complication of pneumonia (particularly Streptococcus pneumoniae) 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
The pneumonias cased by the atypical organisms Mycoplasma and Chlamydia are usually mild. Some research is
suggesting, however, that these organisms, particularly Chlamydia, may have very powerful inflammatory affects in
blood vessels, which can theoretically have certain adverse long?term effects even in healthy younger individuals.
Heart Disease and Stroke. Research has suggested that the C. pneumoniae may trigger the immune system to react.
This may cause inflammation and damage over time in the arteries of the heart and elsewhere, a process called
atherosclerosis or hardening of the arteries. Atherosclerosis can lead to heart attacks and strokes. Studies on a causal
relationship between C. pneumonia and heart disease have been mixed. The most recent ones have found no strong
association between the infection and heart disease while others underplay a possible link.
C. pneumoniae has been associated with a thickening in the carotid artery that leads to the brain, which is a risk factor
for stroke. As with heart disease, however, it is not clear whether the organisms pose any significant risk for stroke.
Asthma. Chlamydia pneumoniae, Mycoplasma pneumoniae, and the respiratory syncytial virus are becoming important
suspects in many cases of severe adult asthma. One small Australian study, for example, found evidence of previous C.
infection in 64% of the asthmatic patients tested. (Serious respiratory infections that occur in early
childhood, however, probably do not play a role in asthma that develops in adulthood.)
General Risk Factors for Community?Acquired Pneumonia (CAP)
Community?acquired pneumonia (CAP) is the most common type and develops outside of the hospital. Each year
between two and four million people in the US develop CAP, and 600,000 people are hospitalized as a result. The
elderly (who tend to have diminished cough and gag reflexes and faltering immune systems) and infants and young
children (who have immature immune systems and small airways) are at greater risk than are young and middle?aged
General Risk Factors for Hospital?Acquired (Nosocomial) Pneumonia
Pneumonia that is contracted in the hospital is called nosocomial pneumonia and affects an estimated five to 10 out of
every 1,000 hospitalized patients every year. People who are hospitalized have a higher risk for developing pneumonia
than those who are not.
Certain individuals, such as the elderly, the very young, and those with chronic or severe medical conditions, are of
course at higher risk.
In addition, the following conditions within the hospital put patients at higher risk:
Surgery, particularly in people over the age of 80. Among the surgical procedures that pose a particular risk

are splenectomy (removal of the spleen), abdominal aortic aneurysm repair, or operations that impair
Being in the intensive care unit (particularly newborns or patients on mechanical ventilators). In one study,

10% of ventilated patients in the ICU developed pneumonia. Ventilated patients who lie flat on their backs are
at particular risk for aspiration pneumonia; raising the patient up may reduce this risk.

Sedation is also a risk factor for patients who are hospitalized.

Hospitalized patients are particularly vulnerable to gram?negative bacteria and staphylococci, which can be very
dangerous, particularly in people who are already ill.
Medical Conditions that Pose Risks for Pneumonia
Chronic Lung Disease. Chronic obstructive lung diseases, including chronic bronchitis and emphysema, affect 15
million people in the US. This condition is a major risk factors for pneumonia.
People With 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 corticosteroids or other
medications that suppress the immune system are also prone to infection.
Gastroesophageal Reflux Disease. Gastroesophageal reflux disease (GERD) is a condition in which acids from the
stomach move up into the esophagus (an action called reflux). Current studies indicate an association between GERD
and various problems that occur in the sinuses, ears, nasal passages, and airways of the lung. People with GERD also
appear to have an above?average risk for chronic bronchitis, chronic sinusitis, emphysema, pulmonary fibrosis (lung
scarring), and recurrent pneumonia. If a person inhales fluid from the esophagus (aspirates) into the lungs, serious
pneumonia can occur. GERD may contribute to these conditions by triggering inflammation in these upper passages. It
is not yet known whether treatment of GERD would also reduce the risk for these respiratory conditions.
Factors Associated with a Higher Risk in Healthy 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
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 10
years to be realized. Toxic fumes, industrial smoke, and other air pollutants may also damage cilia function, which is a
defense again bacteria in the lungs.
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 to the lungs.
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
Diagnostic Difficulties
Diagnostic Difficulties in Community?Acquired Pneumonia (CAP). It is important to determine if the cause of CAP is a
bacteria, atypical bacteria, or virus, since they require different treatments. In children, for example, S. pneumonia is the
most common cause, but respiratory syncytial virus is also an important cause of pneumonia. Although symptoms may
differ among these types, they often overlap and it is often impossible to identify the organism by symptoms alone.
Nevertheless, 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.
Diagnostic Difficulties in Hospital?Acquired Pneumonia (Nosocomial Pneumonia). Diagnosing pneumonia is
particularly difficult in hospitalized patients (called nosocomial pneumonia) for a number of reasons, including the

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.
Medical and Personal History
The patient's history is an important part of the diagnosis of pneumonia. The patient should be sure to report any of the
Recent or chronic respiratory infection

Exposure to people with pneumonia or other respiratory illnesses (such as tuberculosis)

History of smoking

Alcohol or drug abuse

Recent travel

Occupational risks

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 are 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 conditions 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).

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.
Sputum Tests. A sputum sample coughed from the lungs will yield physical information that will help the physician
determine severity. In addition, only a sputum sample will reveal the infecting organism.
Typically, 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 person 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.
The physician will check the sputum for the following indications:
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.
If a good sputum sample is available, it is sent to the laboratory for analysis. In the laboratory, the sample may be used
as follows:
A Gram stain is made, which may reveal the presence of bacteria and whether they are gram?negative or

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

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