Pathogens that can cause pneumonia include
viruses, BACTERIA, and fungi. The pneumonias that
result from these pathogens are contagious—that
is, an infected person can pass them to others
through sneezing and coughing. SPUTUM(mucus
and debris from the respiratory tract) contains the
infective agent. Pneumonia also can develop after
exposure to bacteria aspirated into the lungs (such
as in a person who is weak and vomiting). Noso-
comial pneumonias develop from pathogens com-
mon in environments such as hospitals and skilled
nursing facilities and infect people who are
already weak as a result of other health conditions
(especially those who are IMMUNOCOMPROMISED).
Viral PneumoniaA number of viruses can cause pneumonia, the
most common of which are influenza A, influenza
B, parainfluenza, respiratory syncytial VIRUS, ADEN-
OVIRUS, varicella-zoster virus, EPSTEIN-BARR VIRUS,
and coxsackievirus. CYTOMEGALOVIRUS(CMV) pneu-
monia can develop in people who are IMMUNOCOM-
PROMISED. ANTIVIRAL MEDICATIONSare available for
some of these viral infections and can shorten the
course of the infection and lessen the severity of
symptoms. Most otherwise healthy people recover
fully from viral pneumonia. Bacterial pneumonia
may develop secondarily to viral pneumonia.
Bacterial PneumoniaPneumonia in people over age 30 is more likely to
result from bacterial infection than other causes.
Staphylococcus aureus, Haemophilus influenzaetype b
(Hib), Chlamydia pneumoniae, and Streptococcus pneu-
moniaeare the strains of bacteria most commonly
responsible for bacterial pneumonia. S. pneumoniae
causes the most common form of bacterial pneu-
monia, pneumococcal pneumonia, which often
follows a viral infection of the upper respiratory
tract. Hib pneumonia, despite the bacterium’s
name, has nothing to do with the influenza virus
and affects primarily young children. Hib vaccina-
tion has nearly eliminated this type of pneumonia
among children in the United States. S. aureus
tends to be opportunistic and accounts for about
20 percent of nosocomial pneumonia. ANTIBIOTIC
MEDICATIONSare necessary to treat bacterial pneu-
monia. Even with antibiotic therapy, however,
bacterial pneumonia is a serious illness that can be
deadly among the very young and the very old.Mycoplasmal Pneumonia
Mycoplasma are tiny organisms related to bacte-
ria, commonly called atypical bacteria. The pneu-
monia they cause is typically mild though tends to
linger. A common nickname for mycoplasmal
pneumonia as “walking pneumonia” because its
symptoms are enough to make people feel unwell
though usually not enough to interrupt regular
activities. Most people recover without treatment,
though antibiotics usually speed recovery. COUGH
and HEADACHEmay persist for several weeks.Fungal Pneumonia
Fungi may cause pneumonia in people who take
antibiotics for an extended period of time, as
antibiotics suppress the NORMAL FLORA (normally
present bacteria) that otherwise keep fungi in
check. Fungal pneumonias are rare but when
invasive in someone who is immunocompro-
mised, they can be life-threatening.Pneumocystic Carinii Pneumonia
Pneumocystis cariniiis an opportunistic pneumonia
that occurs nearly exclusively in people who are
immunocompromised, including those who have
HIV/AIDS, are receiving IMMUNOSUPPRESSIVE THER-
APYfollowing organ transplantation, or are under-
going chemotherapy for cancer treatment. During
the early days of the AIDS epidemic, P. carinii
pneumonia was often the first indication that a
person had HIV/AIDS. Doctors may prescribe pro-
phylactic ANTIFUNGAL MEDICATIONSfor people at risk
for P. carinii pneumonia. Such prophylaxis has
now made Pneumocystic pneumonia a relatively
rare event in people whose HIV infection is well-
managed.Symptoms and Diagnostic Path
The symptoms of pneumonia vary somewhat with
the type of pneumonia, though commonly include- cough that produces greenish yellow sputum or
HEMOPTYSIS(bloody sputum) - FEVER(sometimes high)
- chills or sweating
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