C h a p t e r 2 2
Respiratory Tract Infections, Neoplasms, and Childhood Disorders
545
the alveolar septum and the interstitium of the lung
(Fig. 22-3B). They produce less striking symptoms and
physical findings than bacterial pneumonia; there is a
lack of alveolar infiltration and purulent sputum, leu-
kocytosis, and lobar consolidation on the radiograph.
Acute bacterial pneumonias can be classified as lobar
pneumonia or bronchopneumonia, based on their ana-
tomic pattern of distribution.
14
In general,
lobar pneu-
monia
refers to consolidation of a part or all of a lung
lobe, and
bronchopneumonia
signifies a patchy consoli-
dation involving more than one lobe (Fig. 22-4).
Community-AcquiredPneumonia.
Theterm
community-
acquired pneumonia
is used to describe infections from
organisms found in the community rather than in the
hospital or nursing home. It is defined as an infection
that begins outside the hospital or is diagnosed within
48 hours after admission to the hospital in a person who
has not resided in a long-term care facility for 14 days
or more before admission.
20–23
Community-acquired
pneumonia may be further categorized according to risk
of mortality and need for hospitalization based on age,
presence of coexisting disease, and severity of illness,
using physical examination, laboratory, and radiologic
findings.
Community-acquired pneumonia may be either bac-
terial or viral.
14,20–23
The most common cause of infec-
tion in all categories is
S. pneumoniae.
Other common
pathogens include
H. influenzae, S. aureus,
and gram-
negative bacilli. Less common agents are
Mycoplasma
pneumoniae, Chlamydia
species, and viruses, some-
times called
atypical agents.
Common viral causes of
community-acquired pneumonia include the influenza
virus, respiratory syncytial virus, adenovirus, and para-
influenza virus.
The methods used in the diagnosis of community-
acquired pneumonia depend on age, coexisting health
problems, and the severity of illness. In persons younger
than 65 years of age and without coexisting disease,
the diagnosis usually is based on history and physical
examination, chest radiographs, and knowledge of the
microorganisms currently causing infections in the com-
munity. Sputum specimens may be obtained for staining
procedures and culture. Blood cultures may be done for
persons requiring hospitalization.
Treatment involves the use of appropriate antibiotic
therapy. Empiric antibiotic therapy, based on knowledge
regarding an antibiotic’s spectrum of action and abil-
ity to penetrate bronchopulmonary secretions, often is
used for persons with community-acquired pneumonia
who do not require hospitalization. Hospitalization and
more intensive care may be required depending on the
person’s age, preexisting health status, and severity of
the infection.
Hospital-Acquired Pneumonia.
Hospital-acquired,
or nosocomial, pneumonia is defined as a lower respi-
ratory tract infection that was not present or incubat-
ing on admission to the hospital. Usually, infections
occurring 48 hours or more after admission are con-
sidered hospital acquired.
14,24,25
Persons requiring intu-
bation and mechanical ventilation are particularly at
risk, as are those with compromised immune function,
chronic lung disease, and airway instrumentation, such
as endotracheal intubation or tracheotomy. Ventilator-
associated pneumonia is pneumonia that develops in
mechanically ventilated patients more than 48 hours
after intubation.
A
Alveolar
lumen
Interstitium
B
FIGURE 22-3.
Location of inflammatory processes in
(A)
typical
and
(B)
atypical forms of pneumonia.
A
B
FIGURE 22-4.
Distribution of lung involvement in
(A)
lobar
pneumonia and
(B)
bronchopneumonia.
