Encyclopedia of Health and Medicine

pneumonia 221
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). Nosocomial
pneumonias develop from pathogens common
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 Pneumonia
A 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) pneumonia
can develop in people who are IMMUNOCOM-
PROMISED. ANTIVIRAL MEDICATIONS are 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 Pneumonia
Pneumonia in people over age 30 is more likely to
result from bacterial infection than other causes.
Staphylococcus aureus, Haemophilus influenzae type b
(Hib), Chlamydia pneumoniae, and Streptococcus pneumoniae
are the strains of bacteria most commonly
responsible for bacterial pneumonia. S. pneumoniae
causes the most common form of bacterial pneumonia,
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 vaccination
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
MEDICATIONS are necessary to treat bacterial pneumonia.
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 bacteria,
commonly called atypical bacteria. The pneumonia
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 HEADACHE may 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 immunocompromised,
they can be life-threatening.
Pneumocystic Carinii Pneumonia
Pneumocystis carinii is an opportunistic pneumonia
that occurs nearly exclusively in people who are
immunocompromised, including those who have
HIV/AIDS, are receiving IMMUNOSUPPRESSIVE THER-
APY following organ transplantation, or are undergoing
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 prophylactic
ANTIFUNGAL MEDICATIONS for people at risk
for P. carinii pneumonia. Such prophylaxis has
now made Pneumocystic pneumonia a relatively
rare event in people whose HIV infection is wellmanaged.
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