Pneumonia is an abnormal
inflammatory condition of the
lung. It is often characterized as including
inflammation of the
parenchyma of the
lung (that is, the
alveoli)
and
abnormal alveolar filling with fluid (
consolidation and
exudation).
The alveoli are microscopic air-filled sacs in the lungs
responsible for absorbing oxygen. Pneumonia can result from a
variety of causes, including
infection
with
bacteria,
viruses,
fungi, or
parasites, and chemical or physical injury to the
lungs. Its cause may also be officially described as
idiopathic—that is,
unknown—when infectious causes have been excluded.
Typical symptoms associated with pneumonia include
cough,
chest pain,
fever, and
difficulty
in breathing.
Diagnostic tools
include x-rays and examination of the
sputum.
Treatment depends on the cause of pneumonia; bacterial pneumonia is
treated with
antibiotics.
Pneumonia is a common illness which occurs in all age groups, and
is a leading cause of death among the elderly and people who are
chronically and
terminally ill. Additionally, it is the
leading cause of death in children under five years old worldwide.
Vaccines to prevent certain types of
pneumonia are available. The
prognosis
depends on the type of pneumonia, the appropriate treatment, any
complications, and the person's underlying health.
Classification
Pneumonias can be classified in several ways. Pathologists
originally classified them according to the
anatomic changes that were found in the lungs during
autopsies. As more became known about the
microorganisms causing pneumonia, a
microbiologic classification arose, and with
the advent of
x-rays, a
radiological classification. Another important
system of classification is the combined clinical classification,
which combines factors such as age, risk factors for certain
microorganisms, the presence of underlying lung disease and
underlying systemic disease, and whether the person has recently
been hospitalized.
Early classification schemes
Initial descriptions of pneumonia focused on the
anatomic or
pathologic
appearance of the lung, either by direct inspection at
autopsy or by its appearance under a
microscope.
- A lobar pneumonia is an
infection that only involves a single lobe, or section, of a
lung. Lobar pneumonia is often due to
Streptococcus
pneumoniae (though Klebsiella pneumoniae is also
possible.)
- Multilobar pneumonia involves more than one lobe, and
it often causes a more severe illness.
- Bronchial pneumonia affects
the lungs in patches around the tubes (bronchi or
bronchioles).
- Interstitial
pneumonia involves the areas in between the alveoli, and it may
be called "interstitial pneumonitis." It is more likely to be
caused by viruses or by atypical bacteria.
The discovery of x-rays made it possible to determine the anatomic
type of pneumonia without direct examination of the lungs at
autopsy and led to the development of a
radiological classification. Early investigators
distinguished between typical lobar pneumonia and atypical (e.g.
Chlamydophila) or viral pneumonia using the location, distribution,
and appearance of the opacities they saw on chest x-rays. Certain
x-ray findings can be used to help predict the course of illness,
although it is not possible to clearly determine the microbiologic
cause of a pneumonia with x-rays alone.
With the advent of modern microbiology, classification based upon
the causative microorganism became possible. Determining which
microorganism is causing an individual's pneumonia is an important
step in deciding treatment type and length. Sputum cultures, blood
cultures, tests on respiratory secretions, and specific blood tests
are used to determine the microbiologic classification. Because
such laboratory testing typically takes several days, microbiologic
classification is usually not possible at the time of initial
diagnosis.
Combined clinical classification
Traditionally, clinicians have classified pneumonia by clinical
characteristics, dividing them into "acute" (less than three weeks
duration) and "chronic" pneumonias. This is useful because chronic
pneumonias tend to be either non-infectious, or mycobacterial,
fungal, or mixed bacterial infections caused by airway obstruction.
Acute pneumonias are further divided into the classic bacterial
bronchopneumonias (such as
Streptococcus pneumoniae), the
atypical pneumonias (such as the interstitial pneumonitis of
Mycoplasma pneumoniae
or
Chlamydia
pneumoniae), and the aspiration pneumonia syndromes.
Chronic pneumonias, on the other hand, mainly include those of
Nocardia,
Actinomyces and
Blastomyces dermatitidis, as
well as the granulomatous pneumonias (
Mycobacterium tuberculosis
and
atypical mycobacteria,
Histoplasma
capsulatum and
Coccidioides immitis). Table 13-7
in:
The combined clinical classification, now the most commonly used
classification scheme, attempts to identify a person's risk factors
when he or she first comes to medical attention. The advantage of
this classification scheme over previous systems is that it can
help guide the selection of appropriate initial treatments even
before the microbiologic cause of the pneumonia is known. There are
two broad categories of pneumonia in this scheme:
community-acquired pneumonia and hospital-acquired pneumonia. A
recently introduced type of
healthcare-associated
pneumonia (in patients living outside the hospital who have
recently been in close contact with the health care system) lies
between these two categories.
Community-acquired pneumonia
Community-acquired
pneumonia (CAP) is infectious pneumonia in a person who has not
recently been hospitalized. CAP is the most common type of
pneumonia. The most common causes of CAP vary depending on a
person's age, but they include
Streptococcus pneumoniae,
viruses, the atypical bacteria, and
Haemophilus influenzae. Overall,
Streptococcus pneumoniae is the most common cause of
community-acquired pneumonia worldwide.
Gram-negative bacteria cause CAP in
certain at-risk populations.
CAP is the fourth most common cause of death
in the United
Kingdom
and the sixth in the United States
. The term "walking pneumonia" has been used
to describe a type of community-acquired pneumonia of less severity
(because of the fact that the sufferer can continue to "walk"
rather than require hospitalization). Walking pneumonia is usually
caused by the atypical bacterium,
Mycoplasma pneumoniae.
Hospital-acquired pneumonia
Hospital-acquired pneumonia, also called
nosocomial pneumonia, is pneumonia
acquired during or after hospitalization for another illness or
procedure with onset at least 72 hrs after admission. The causes,
microbiology, treatment and prognosis are different from those of
community-acquired pneumonia. Up to 5% of patients admitted to a
hospital for other causes subsequently develop pneumonia.
Hospitalized patients may have many risk factors for pneumonia,
including
mechanical
ventilation, prolonged
malnutrition, underlying
heart and
lung diseases, decreased
amounts of stomach acid, and immune disturbances. Additionally, the
microorganisms a person is exposed to in a hospital are often
different from those at home . Hospital-acquired microorganisms may
include resistant bacteria such as
MRSA,
Pseudomonas,
Enterobacter, and
Serratia. Because individuals with
hospital-acquired pneumonia usually have underlying illnesses and
are exposed to more dangerous bacteria, it tends to be more deadly
than community-acquired pneumonia.
Ventilator-associated
pneumonia (VAP) is a subset of hospital-acquired pneumonia. VAP
is pneumonia which occurs after at least 48 hours of
intubation and
mechanical ventilation.
Other types of pneumonia
- SARS
is a highly contagious and deadly type of pneumonia which first
occurred in 2002 after initial outbreaks in China
. SARS
is caused by the SARS coronavirus,
a previously unknown pathogen.
- BOOP is caused by inflammation of the small airways of the
lungs. It is also known as cryptogenic organizing pneumonitis
(COP).
- Eosinophilic pneumonia is invasion of the lung by eosinophils, a particular kind of white blood cell. Eosinophilic pneumonia
often occurs in response to infection with a parasite or after exposure to certain types of
environmental factors.
- Chemical pneumonia (usually called chemical pneumonitis) is caused by
chemical toxicants such as pesticides, which may enter the body by inhalation or by skin contact. When the toxic
substance is an oil, the pneumonia may be called lipoid
pneumonia.
- Aspiration pneumonia (or aspiration pneumonitis) is caused by
aspirating foreign objects
which are usually oral or gastric contents, either while eating, or
after reflux or vomiting which results in bronchopneumonia. The resulting lung
inflammation is not an infection but can contribute to one, since
the material aspirated may contain anaerobic bacteria or other unusual
causes of pneumonia. Aspiration is a leading cause of death among
hospital and nursing home patients,
since they often cannot adequately protect their airways and may
have otherwise impaired defenses.
- Dust pneumonia describes disorders caused by excessive exposure
to dust storms, particularly during the
Dust Bowl in the United States. With dust
pneumonia, dust settles all the way into the alveoli of the lungs,
stopping the cilia from moving and preventing the lungs from ever
clearing themselves.
- Necrotizing pneumonia, although overlapping
with many other classifications, includes pneumonias that cause
substantial necrosis of lung cells, and
sometimes even lung abscess. Implicated
bacteria are extremely commonly anaerobic bacteria, with or without
additional facultatively anaerobic ones like Staphylococcus aureus, Klebsiella pneumoniae and Streptococcus pyogenes. Table 13-7
in: Type 3 pneumococcus is
uncommonly implicated.
- Opportunistic pneumonia includes those that
frequently strike immunocompromised victims. Main pathogens
are cytomegalovirus, Pneumocystis jiroveci, Mycobacterium
avium-intracellulare, invasive aspergillosis, invasive candidiasis, as well as the "usual bacteria"
that strike immunocompetent people as well.
Signs and symptoms
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Main symptoms of infectious
pneumonia
People with infectious pneumonia often have a cough producing
greenish or yellow
sputum, or
phlegm and a high
fever that may
be accompanied by
shaking chills.
Shortness of breath is also common, as
is pleuritic
chest pain, a sharp or
stabbing pain, either experienced during deep breaths or coughs or
worsened by them. People with pneumonia may
cough up blood, experience
headaches, or develop
sweaty and clammy skin. Other possible symptoms
are
loss of appetite, fatigue,
blueness of the skin,
nausea,
vomiting, mood
swings, and
joint pains or
muscle aches. Less common forms of pneumonia can
cause other symptoms; for instance, pneumonia caused by
Legionella may cause abdominal
pain and
diarrhea, while pneumonia caused
by
tuberculosis or
Pneumocystis may cause only
weight loss and
night sweats. In elderly people
manifestations of pneumonia may not be typical. They may develop a
new or worsening confusion or may experience unsteadiness, leading
to falls. Infants with pneumonia may have many of the symptoms
above, but in many cases they are simply sleepy or have a decreased
appetite.
Symptoms of pneumonia need immediate medical evaluation.
Physical examination by a health care
provider may reveal
fever or sometimes
low body temperature, an
increased respiratory rate,
low blood pressure, a
high heart rate, or a low
oxygen saturation, which is the amount of
oxygen in the blood as indicated by either
pulse oximetry or
blood gas analysis. People who are
struggling to breathe, who are confused, or who have
cyanosis (blue-tinged skin) require immediate
attention.
Physical examination of the
lungs may be normal, but often shows decreased expansion of the
chest on the affected side,
bronchial
breathing on auscultation with a
stethoscope (harsher sounds from the larger
airways transmitted through the inflamed and consolidated lung),
and
rales (or crackles) heard over the
affected area during inspiration.
Percussion may be dulled over the
affected lung, but increased rather than decreased
vocal resonance (which distinguishes it
from a
pleural effusion). While
these signs are relevant, they are insufficient to diagnose or rule
out a pneumonia; moreover, in studies it has been shown that two
doctors can arrive at different findings on the same patient.
Cause
Pneumonia can be caused by microorganisms, irritants and unknown
causes. When pneumonias are grouped this way, infectious causes are
the most common type.
The symptoms of infectious pneumonia are caused by the invasion of
the lungs by
microorganisms and by the
immune system's response to the
infection. Although more than one hundred strains of microorganism
can cause pneumonia, only a few are responsible for most cases. The
most common causes of pneumonia are
viruses
and
bacteria. Less common causes of
infectious pneumonia are
fungi and
parasites.
Viruses
Viruses invade cells in order to reproduce. Typically, a virus
reaches the lungs when airborne droplets are inhaled through the
mouth and
nose. Once in
the lungs, the virus invades the cells lining the airways and
alveoli. This invasion often leads to cell death, either when the
virus directly kills the cells, or through a type of cell
controlled self-destruction called
apoptosis. When the immune system responds to the
viral infection, even more lung damage occurs.
White blood cells, mainly
lymphocytes, activate certain chemical
cytokines which allow fluid to leak into the
alveoli. This combination of cell destruction and fluid-filled
alveoli interrupts the normal transportation of oxygen into the
bloodstream.
As well as damaging the lungs, many viruses affect other
organ and thus disrupt many body functions.
Viruses can also make the body more susceptible to bacterial
infections; for which reason bacterial pneumonia often complicates
viral pneumonia.
Viral pneumonia is commonly caused by viruses such as
influenza virus,
respiratory syncytial virus
(RSV),
adenovirus, and
metapneumovirus.
Herpes simplex virus is a rare cause of
pneumonia except in newborns. People with weakened immune systems
are also at risk of pneumonia caused by
cytomegalovirus (CMV).
Bacteria
Bacteria typically enter the lung when airborne droplets are
inhaled, but can also reach the lung through the bloodstream when
there is an infection in another part of the body. Many bacteria
live in parts of the
upper
respiratory tract, such as the nose, mouth and sinuses, and can
easily be inhaled into the alveoli. Once inside, bacteria may
invade the spaces between cells and between alveoli through
connecting pores. This invasion triggers the
immune system to send
neutrophils, a type of defensive white blood
cell, to the lungs. The neutrophils
engulf and kill the offending organisms, and
also release
cytokines, causing a general
activation of the immune system. This leads to the fever, chills,
and fatigue common in bacterial and fungal pneumonia. The
neutrophils, bacteria, and fluid from surrounding blood vessels
fill the alveoli and interrupt normal oxygen transportation.
Bacteria often travel from an infected lung into the bloodstream,
causing serious or even fatal illness such as
septic shock, with low blood pressure and
damage to multiple parts of the body including the
brain,
kidneys, and
heart. Bacteria can also travel to the area between
the lungs and the chest wall (the
pleural
cavity) causing a complication called an
empyema.
The most common causes of bacterial pneumonia are
Streptococcus
pneumoniae and "atypical" bacteria. Atypical bacteria are
parasitic bacteria that live
intracellular or do not have a cell
wall. Moreover they cause generally less severe pneumonia, thus
atypical symptoms, and respond to different antibiotics than other
bacteria.
The types of
Gram-positive bacteria
that cause pneumonia can be found in the nose or mouth of many
healthy people.
Streptococcus pneumoniae,
often called "pneumococcus", is the most common bacterial cause of
pneumonia in all age groups except newborn infants. Pneumococcus
kills approximately one million children annually, mostly in
developing countries.World Health Organization. Acute Respiratory
Infections:
Streptococcus pneumoniae. Another
important Gram-positive cause of pneumonia is
Staphylococcus aureus, with
Streptococcus
agalactiae being an important cause of pneumonia in
newborn babies.
Gram-negative bacteria
cause pneumonia less frequently than gram-positive bacteria. Some
of the gram-negative bacteria that cause pneumonia include
Haemophilus
influenzae,
Klebsiella pneumoniae,
Escherichia coli,
Pseudomonas aeruginosa and
Moraxella
catarrhalis. These bacteria often live in the
stomach or intestines and may enter
the lungs if vomit is inhaled.
"Atypical" bacteria which cause
pneumonia include
Chlamydophila pneumoniae,
Mycoplasma
pneumoniae, and
Legionella pneumophila.
Fungi
Fungal pneumonia is uncommon, but it may occur in individuals with
immune system problems due to
AIDS,
immunosuppresive drugs, or other
medical problems. The pathophysiology of pneumonia caused by fungi
is similar to that of bacterial pneumonia. Fungal pneumonia is most
often caused by
Histoplasma
capsulatum, blastomyces,
Cryptococcus neoformans,
Pneumocystis
jiroveci, and
Coccidioides immitis.
Histoplasmosis is most common in the
Mississippi River basin, and
coccidioidomycosis in the
southwestern United States.
Parasites
A variety of parasites can affect the lungs. These parasites
typically enter the body through the skin or by being swallowed.
Once inside, they travel to the lungs, usually through the blood.
There, as in other cases of pneumonia, a combination of cellular
destruction and immune response causes disruption of oxygen
transportation. One type of white blood cell, the
eosinophil, responds vigorously to parasite
infection. Eosinophils in the lungs can lead to
eosinophilic pneumonia, thus
complicating the underlying parasitic pneumonia. The most common
parasites causing pneumonia are
Toxoplasma gondii,
Strongyloides stercoralis,
and
Ascariasis.
Idiopathic
Idiopathic interstitial pneumonias (IIP) are a class of
diffuse lung diseases. In some types of
IIP, e.g. some types of
usual interstitial pneumonia,
the cause, indeed, is unknown or idiopathic. In some types of IIP
the cause of the pneumonia is known, e.g.
desquamative interstitial
pneumonia is caused by
smoking, and the
name is a
misnomer.
Diagnosis
If pneumonia is suspected on the basis of a patient's
symptoms and findings from
physical examination, further
investigations are needed to confirm the diagnosis. Information
from a
chest X-ray and
blood tests are helpful, and sputum
culture in some cases. The chest
X-ray is typically used for diagnosis in hospitals and some clinics
with X-ray facilities. However, in a community setting (
general practice), pneumonia is usually
diagnosed based on symptoms and physical examination alone.
Diagnosing pneumonia can be difficult in some people, especially
those who have other illnesses. Occasionally a chest
CT scan or other tests may be needed to distinguish
pneumonia from other illnesses.
Investigations
An important test for pneumonia in unclear situations is a chest
x-ray. Chest x-rays can reveal areas of
opacity (seen as white) which
represent consolidation. Pneumonia is not always seen on x-rays,
either because the disease is only in its initial stages, or
because it involves a part of the lung not easily seen by x-ray. In
some cases, chest CT (
computed
tomography) can reveal pneumonia that is not seen on chest
x-ray. X-rays can be misleading, because other problems, like lung
scarring and
congestive heart
failure, can mimic pneumonia on x-ray. Chest x-rays are also
used to evaluate for complications of pneumonia (
see below.)
If antibiotics fail to improve the patient's health, or if the
health care provider has concerns about the diagnosis, a
culture of the person's
sputum may be requested. Sputum cultures generally
take at least two to three days, so they are mainly used to confirm
that the infection is sensitive to an antibiotic that has already
been started. A blood sample may similarly be
cultured to look for bacteria in the blood.
Any bacteria identified are then tested to see which antibiotics
will be most effective.
A
complete blood count may show
a
high white blood cell count,
indicating the presence of an infection or inflammation. In some
people with
immune system
problems, the white blood cell count may appear deceptively
normal. Blood tests may be used to evaluate
kidney function (important when prescribing certain
antibiotics) or to look for
low blood
sodium. Low blood sodium in pneumonia is thought to be due to
extra
anti-diuretic hormone
produced when the lungs are diseased (
SIADH).
Specific blood
serology tests for other
bacteria (
Mycoplasma,
Legionella and
Chlamydophila) and a
urine test for
Legionella antigen are available.
Respiratory secretions can also be tested for the presence of
viruses such as
influenza,
respiratory syncytial virus, and
adenovirus.
Liver function tests should be carried
out to test for damage caused by sepsis.
Combining findings
One study created a prediction rule that found the five following
signs best predicted infiltrates on the chest radiograph of 1134
patients presenting to an emergency room:
- Temperature > 100 degrees F (37.8 degrees C)
- Pulse > 100 beats/min
- Rales/crackles
- Decreased breath sounds
- Absence of asthma
The probability of an infiltrate in two separate validations was
based on the number of findings:
- 5 findings - 84% to 91% probability
- 4 findings - 58% to 85%
- 3 findings - 35% to 51%
- 2 findings - 14% to 24%
- 1 findings - 5% to 9%
- 0 findings - 2% to 3%
A subsequent study comparing four prediction rules to physician
judgment found that two rules, the one above and also were more
accurate than physician judgment because of the increased
specificity of the prediction rules.
Differential diagnosis
Several diseases and/or conditions can present with similar
clinical features to pneumonia and as such care must be taken in
the proper diagnosis of the disease.
Chronic obstructive
pulmonary disease (COPD) or
asthma can
present with a
polyphonic wheeze, similar
to that of pneumonia.
Pulmonary
edema can be mistaken for pneumonia due to its ability to show
a third heart sound and present with an abnormal
ECG. Other diseases to be taken into
consideration include
bronchiectasis,
lung cancer and
pulmonary emboli.
Prevention
There are several ways to prevent infectious pneumonia.
Appropriately treating underlying illnesses (such as
AIDS) can decrease a person's risk of pneumonia.
Smoking cessation is important not
only because it helps to limit lung damage, but also because
cigarette smoke interferes with many of the body's natural defenses
against pneumonia.
Research shows that there are several ways
to prevent pneumonia in newborn
infants.
Testing pregnant women for
Group B
Streptococcus and
Chlamydia trachomatis, and then
giving
antibiotic treatment if needed,
reduces pneumonia in infants. Suctioning the mouth and throat of
infants with
meconium-stained
amniotic fluid decreases the rate of
aspiration pneumonia.
Vaccination is important for preventing
pneumonia in both children and adults. Vaccinations against
Haemophilus
influenzae and
Streptococcus pneumoniae in
the first year of life have greatly reduced the role these bacteria
play in causing pneumonia in children. Vaccinating children against
Streptococcus pneumoniae has also led to a decreased
incidence of these infections in adults because many adults acquire
infections from children. Hib vaccine is now widely used around the
globe. The childhood pneumococcal vaccine is still as of 2009
predominantly used in high-income countries, though this is
changing. In 2009, Rwanda became the first low-income country to
introduce pneumococcal conjugate vaccine into their national
immunization program.
A
vaccine against
Streptococcus pneumoniae is also available for adults.
In the U.S., it is currently recommended for all healthy
individuals older than 65 and any adults with
emphysema,
congestive heart failure,
diabetes mellitus,
cirrhosis of the
liver,
alcoholism,
cerebrospinal fluid leaks, or those who
do not have a
spleen. A repeat vaccination
may also be required after five or ten years.
Influenza vaccines should be given
yearly to the same individuals who receive vaccination against
Streptococcus
pneumoniae. In addition, health care workers, nursing home
residents, and pregnant women should receive the vaccine. When an
influenza outbreak is occurring, medications such as
amantadine,
rimantadine,
zanamivir,
and
oseltamivir can help prevent
influenza.
Treatment
Most cases of pneumonia can be treated without hospitalization.
Typically, oral antibiotics, rest, fluids, and
home care are sufficient for complete resolution.
However, people with pneumonia who are having trouble breathing,
people with other medical problems, and the elderly may need more
advanced treatment. If the symptoms get worse, the pneumonia does
not improve with home treatment, or complications occur, the person
will often have to be hospitalized.
Bacterial pneumonia
Antibiotics are used to treat bacterial
pneumonia. In contrast, antibiotics are not useful for
viral pneumonia, although they sometimes are
used to treat or prevent bacterial infections that can occur in
lungs damaged by a viral pneumonia. The antibiotic choice depends
on the nature of the pneumonia, the most common microorganisms
causing pneumonia in the local geographic area, and the immune
status and underlying health of the individual. Treatment for
pneumonia should ideally be based on the causative microorganism
and its known
antibiotic
sensitivity. However, a specific cause for pneumonia is
identified in only 50% of people, even after extensive evaluation.
Because treatment should generally not be delayed in any person
with a serious pneumonia,
empiric
treatment is usually started well before laboratory reports are
available.
In the United Kingdom
, amoxicillin and
clarithromycin or erythromycin are the antibiotics selected for
most patients with community-acquired pneumonia; patients allergic
to penicillins are given erythromycin instead of amoxicillin. In
North America, where the "atypical"
forms of community-acquired pneumonia are becoming more common,
macrolides (such as
azithromycin and
clarithromycin), the
fluoroquinolones, and
doxycycline have displaced amoxicillin as
first-line outpatient treatment for
community-acquired pneumonia.
The duration of treatment has traditionally been seven to ten days,
but there is increasing evidence that shorter courses (as short as
three days) are sufficient.
Antibiotics for hospital-acquired pneumonia include third- and
fourth-generation
cephalosporins,
carbapenems,
fluoroquinolones,
aminoglycosides, and
vancomycin. These antibiotics are usually given
intravenously. Multiple
antibiotics may be administered in combination in an attempt to
treat all of the possible causative microorganisms. Antibiotic
choices vary from hospital to hospital because of regional
differences in the most likely microorganisms, and because of
differences in the microorganisms' abilities to resist various
antibiotic treatments.
People who have difficulty breathing due to pneumonia may require
extra
oxygen. Extremely sick individuals may
require
intensive care,
often including
endotracheal
intubation and
artificial
ventilation.
Over the counter
cough medicine has
not been found to be helpful in pneumonia.
Viral pneumonia
Viral pneumonia caused by influenza
A may be treated with
rimantadine or
amantadine, while viral pneumonia caused
by influenza A or B may be treated with
oseltamivir or
zanamivir. These treatments are beneficial only if
they are started within 48 hours of the onset of symptoms. Many
strains of
H5N1 influenza A, also known as
avian influenza or "bird flu," have
shown resistance to rimantadine and amantadine. There are no known
effective treatments for viral pneumonias caused by the
SARS coronavirus,
adenovirus,
hantavirus, or
parainfluenza virus.
Aspiration pneumonia
There is no evidence to support the use of antibiotics in
chemical pneumonitis without bacterial
infection. If infection is present in
aspiration pneumonia, the choice of
antibiotic will depend on several factors, including the suspected
causative organism and whether pneumonia was acquired in the
community or developed in a hospital setting. Common options
include
clindamycin, a combination of a
beta-lactam antibiotic and
metronidazole, or an
aminoglycoside.
Corticosteroids are commonly used in
aspiration pneumonia, but there is no evidence to support their use
either.
Complications
Sometimes pneumonia can lead to additional
complications. Complications are
more frequently associated with bacterial pneumonia than with viral
pneumonia. The most important complications include:
Respiratory and circulatory failure
Because pneumonia affects the lungs, often people with pneumonia
have difficulty breathing, and it may not be possible for them to
breathe well enough to stay alive without support. Non-invasive
breathing assistance may be helpful, such as with a
bi-level positive airway
pressure machine. In other cases, placement of an
endotracheal tube (breathing tube) may be
necessary, and a
ventilator may
be used to help the person breathe.
Pneumonia can also cause respiratory failure by triggering
acute respiratory distress
syndrome (ARDS), which results from a combination of infection
and inflammatory response. The lungs quickly fill with fluid and
become very stiff. This stiffness, combined with severe
difficulties extracting oxygen due to the alveolar fluid, create a
need for mechanical ventilation.
Sepsis and
septic
shock are potential complications of pneumonia. Sepsis occurs
when microorganisms enter the bloodstream and the
immune system responds by secreting
cytokines. Sepsis most often occurs with
bacterial pneumonia;
Streptococcus
pneumoniae is the most common cause. Individuals with sepsis
or septic shock need hospitalization in an
intensive care unit. They often require
intravenous fluids and medications
to help keep their blood pressure from dropping too low. Sepsis can
cause liver, kidney, and heart damage, among other problems, and it
often causes death.
Pleural effusion, empyema, and abscess
Occasionally, microorganisms infecting the lung will cause fluid (a
pleural effusion) to build up in
the space that surrounds the lung (the
pleural cavity). If the microorganisms
themselves are present in the pleural cavity, the fluid collection
is called an
empyema. When pleural fluid is
present in a person with pneumonia, the fluid can often be
collected with a needle (
thoracentesis) and examined. Depending on the
results of this examination, complete drainage of the fluid may be
necessary, often requiring a
chest tube.
In severe cases of empyema,
surgery
may be needed. If the fluid is not drained, the infection may
persist, because antibiotics do not penetrate well into the pleural
cavity.
Rarely, bacteria in the lung will form a pocket of infected fluid
called an
abscess. Lung abscesses can
usually be seen with a chest x-ray or chest CT scan. Abscesses
typically occur in
aspiration
pneumonia and often contain several types of bacteria.
Antibiotics are usually adequate to treat a lung abscess, but
sometimes the abscess must be drained by a
surgeon or
radiologist.
Prognosis
With treatment, most types of bacterial pneumonia can be cleared
within two to four weeks. Viral pneumonia may last longer, and
mycoplasmal pneumonia may take
four to six weeks to resolve completely. The eventual outcome of an
episode of pneumonia depends on how ill the person is when he or
she is first diagnosed.
In the United States, about one of every twenty people with
pneumococcal pneumonia die.
In cases where the pneumonia progresses to blood poisoning
(
bacteremia), just over 20% of sufferers
die.
The death rate (or
mortality) also
depends on the underlying cause of the pneumonia. Pneumonia caused
by
Mycoplasma, for instance, is associated with little
mortality. However, about half of the people who develop
methicillin-resistant
Staphylococcus aureus (
MRSA) pneumonia while on a ventilator will die. In
regions of the world without advanced health care systems,
pneumonia is even deadlier. Limited access to clinics and
hospitals, limited access to x-rays, limited antibiotic choices,
and inability to treat underlying conditions inevitably leads to
higher rates of death from pneumonia. For these reasons, the
majority of deaths in children under five due to pneumococcal
disease occur in developing coutries.
Clinical prediction rules
Clinical prediction rules have been developed to more objectively
prognosticate outcomes in pneumonia. These rules can be helpful in
deciding whether or not to hospitalize the person.
Epidemiology
Pneumonia is a common illness in all parts of the world. It is a
major cause of death among all age groups. In children, many of
these deaths occur in the newborn period. The
World Health Organization
estimates that one in three newborn infant deaths are due to
pneumonia. Over two million children under five die each year
worldwide. WHO also estimates that up to 1 million of these
(vaccine preventable) deaths are caused by the bacteria
Streptococcus pneumoniae, and over 90% of these deaths
take place in developing countries. Mortality from pneumonia
generally decreases with age until late adulthood. Elderly
individuals, however, are at particular risk for pneumonia and
associated mortality. Because of the very high burden of disease in
developing countries and because of a relatively low awareness of
the disease in industrialized countries, the global health
community has declared November 2 to be
World Pneumonia Day, a day for concerned
citizens and policy makers to take action against the
disease.
In the
United
Kingdom
, the annual incidence of pneumonia is approximately
6 cases for every 1000 people for the 18–39 age group. For
those over 75 years of age, this rises to 75 cases for every 1000
people. Roughly 20–40% of individuals who contract pneumonia
require hospital admission of which between 5–10% are admitted to a
critical care unit. Similarly,
the mortality rate in the UK is around 5–10%.
More cases of pneumonia occur during the winter months than during
other times of the year. Pneumonia occurs more commonly in males
than females, and more often in Blacks than Caucasians due to
differences in synthesizing
Vitamin D from
sunlight. Individuals with underlying illnesses such as
Alzheimer's disease,
cystic fibrosis,
emphysema,
tobacco
smoking,
alcoholism, or
immune system problems are at increased
risk for pneumonia. These individuals are also more likely to have
repeated episodes of pneumonia. People who are hospitalized for any
reason are also at high risk for pneumonia.
History
The symptoms of pneumonia were described by
Hippocrates (c. 460 BC – 370 BC):
Peripneumonia, and pleuritic affections, are to be thus
observed: If the fever be acute, and if there be pains on either
side, or in both, and if expiration be if cough be present, and the
sputa expectorated be of a blond or livid color, or likewise thin,
frothy, and florid, or having any other character different from
the common...
When pneumonia is at its height, the case is beyond
remedy if he is not purged, and it is bad if he has dyspnoea, and
urine that is thin and acrid, and if sweats come out about the neck
and head, for such sweats are bad, as proceeding from the
suffocation, rales, and the violence of the disease which is
obtaining the upper hand.
However, Hippocrates referred to pneumonia as a disease "named by
the ancients." He also reported the results of surgical drainage of
empyemas.
Maimonides (1138–1204 AD)
observed "The basic symptoms which occur in pneumonia and which are
never lacking are as follows: acute fever, sticking [pleuritic]
pain in the side, short rapid breaths, serrated
pulse and cough." This clinical description is quite
similar to those found in modern textbooks, and it reflected the
extent of medical knowledge through the
Middle Ages into the 19th century.
Bacteria were first seen in the airways of individuals who died
from pneumonia by
Edwin Klebs in 1875.
Initial work identifying the two common bacterial causes
Streptococcus pneumoniae and
Klebsiella
pneumoniae was performed by
Carl Friedländer and
Albert Fränkel in
1882 and 1884, respectively. Friedländer's initial work introduced
the
Gram stain, a fundamental
laboratory test still used to identify and categorize bacteria.
Christian Gram's paper describing the
procedure in 1884 helped differentiate the two different bacteria
and showed that pneumonia could be caused by more than one
microorganism.
Sir
William Osler, known as "the
father of modern medicine," appreciated the morbidity and mortality
of pneumonia, describing it as the "captain of the men of death" in
1918, as it had overtaken tuberculosis as one of the leading causes
of death in his time. (The phrase was originally coined by John
Bunyan with regard to consumption, or tuberculosis. ) However,
several key developments in the 1900s improved the outcome for
those with pneumonia. With the advent of
penicillin and other antibiotics, modern surgical
techniques, and intensive care in the twentieth century, mortality
from pneumonia dropped precipitously in the developed world.
Vaccination of infants against
Haemophilus influenzae type b
began in 1988 and led to a dramatic decline in cases shortly
thereafter. Vaccination against
Streptococcus pneumoniae
in adults began in 1977 and in children began in 2000, resulting in
a similar decline.
Image gallery
image:Normal AP.JPG|Normal AP CXRimage:Normal_L.JPG|Normal lateral
CXRImage:LLL_pneumonia_with_effusionM.jpg|AP CXR showing left lower
lobe pneumonia associated with a small left sided pleural
effusionImage:RLL_pneumoniaM.jpg|AP CXR showing right lower lobe
pneumoniaImage:RLL_pneumoniaLM.jpg|A lateral CXR showing right
lower lobe pneumonia
Image:PneumonisWedge09.JPG|A very prominent wedge shaped pneumonia
on the right.
See also
References
- World Health Organization. Global causes of under 5 mortality.
http://www.who.int/entity/child_adolescent_health/media/causes_death_u5_neonates_2004.pdf.
- PneumoADIP. Vaccine Introduction: Rwanda.
- , specifically, "The chest radiograph usually clears within
4 weeks in patients younger than 50 years without underlying
pulmonary disease". Symptoms are often resolved within 1–2
weeks.]
- Infections: Pneumonia - kidshealth.com
- Hippocrates On Acute Diseases wikisource link
- Maimonides, Fusul Musa ("Pirkei Moshe").
External links