WORLD OF MICROBIOLOGY AND IMMUNOLOGY Poliomyelitis and polio445•
ach contents with their resident bacteria), as well as diabetes,
sickle cell anemia, lymphoma, leukemia, and emphysema.
Pneumonia is one of the most frequent infectious com-
plications of all types of surgeries. Many drugs used during
and after surgery may increase the risk of aspiration, impair
the cough reflex, and cause a patient to underfill their lungs
with air. Pain after surgery also discourages a patient from
breathing deeply and coughing effectively.
The list of organisms which can cause pneumonia is
very large, and includes nearly every class of infecting organ-
ism: viruses, bacteria, bacteria-like organisms, fungi, and par-
asites (including certain worms). Different organisms are
more frequently encountered by different age groups.
Furthermore, other characteristics of the host may place an
individual at greater risk for infection by particular types of
organisms.
Viruses, especially respiratory syncytial virus, parain-
fluenza and influenzaviruses, and adenovirus, cause the
majority of pneumonias in young children. Pneumonia in
older children and young adults is often caused by the bacte-
ria-like Mycoplasma pneumoniae.Adults are more frequently
infected with bacteria (such as Streptococcuspneumoniae,
Hemophilus inflenzae,and Staphylococcus aureus).
The parasite Pneumocystis cariniiis an extremely
important cause of pneumonia in patients with immune prob-
lems, such as patients being treated for cancer with
chemotherapy, or patients with AIDS. People who have rea-
son to come in contact with bird droppings, such as poultry
workers, are at risk for pneumonia caused by the parasite
Chlamydia psittaci.A very large, serious outbreak of pneumo-
nia occurred in 1976, when many people attending an
American Legion convention were infected by a previously
unknown organism (subsequently named Legionella pneu-
mophila) which was traced to air conditioning units in the con-
vention hotel.
Pneumonia is suspected in any patient who presents
with fever, cough, chest pain, shortness of breath, and
increased respirations (number of breaths per minute). Fever
with a shaking chill is even more suspicious, and many
patients cough up clumps of mucus (sputum) that may appear
streaked with pus or blood. Severe pneumonia results in the
signs of oxygen deprivation, including blue appearance of the
nail beds (cyanosis).
The invading organism causes symptoms, in part, by
provoking an overly exuberant immune response in the lungs.
The small blood vessels in the lungs (capillaries) become
leaky, and protein-rich fluid seeps into the alveoli. This results
in less functional area for oxygen-carbon dioxide exchange.
The patient becomes relatively oxygen deprived, while retain-
ing potentially damaging carbon dioxide. The patient breathes
faster, in an effort to bring in more oxygen and blow off more
carbon dioxide.
Mucus production is increased, and the leaky capillaries
may tinge the mucus with blood. Mucus plugs actually further
decrease the efficiency of gas exchange in the lung. The alve-
oli fill further with fluid and debris from the large number of
white blood cells being produced to fight the infection.Consolidation, a feature of bacterial pneumonias,
occurs when the alveoli, which are normally hollow air spaces
within the lung, instead become solid, due to quantities of
fluid and debris.
Viral pneumonias and mycoplasma pneumonias do not
result in consolidation. These types of pneumonia primarily
infect the walls of the alveoli and the parenchyma of the lung.
Diagnosis is for the most part based on the patient’s
report of symptoms, combined with examination of the chest.
Listening with a stethoscope will reveal abnormal sounds, and
tapping on the patient’s back (which should yield a resonant
sound due to air filling the alveoli) may instead yield a dull
thump if the alveoli are filled with fluid and debris.
Laboratory diagnosis can be made of some bacterial
pneumonias by staining sputum with special chemicals and
looking at it under a microscope. Identification of the spe-
cific type of bacteria may require culturing the sputum
(using the sputum sample to grow greater numbers of the
bacteria in a lab dish).
X-ray examination of the chest may reveal certain
abnormal changes associated with pneumonia. Localized
shadows obscuring areas of the lung may indicate a bacterial
pneumonia, while streaky or patchy appearing changes in the
x-ray picture may indicate viral or mycoplasma pneumonia.
These changes on x-ray, however, are known to lag in time
behind the patient’s actual symptoms.
Antibiotics, especially given early in the course of the
disease, are very effective against bacterial causes of pneumo-
nia. Erythromycin and tetracycline improve recovery time for
symptoms of mycoplasma pneumonia, but do not eradicate the
organisms. Amantadine and acyclovir may be helpful against
certain viral pneumonias.
Because many bacterial pneumonias occur in patients
who are first infected with the influenza virus (the flu), yearly
vaccinationagainst influenza can decrease the risk of pneu-
monia for certain patients, particularly the elderly and people
with chronic diseases (such as asthma, cystic fibrosis, other
lung or heart diseases, sickle cell disease, diabetes, kidney dis-
ease, and forms of cancer). A specific vaccine against
Streptococcuspneumoniae is very protective, and should be
administered to patients with chronic illnesses. Patients who
have decreased immune resistance (due to treatment with
chemotherapy for various forms of cancer or due to infection
with the AIDS virus), and therefore may be at risk for infec-
tion with Pneumocystis carinii,are frequently put on a regular
drug regimen of Trimethoprim sulfa and/or inhaled pentami-
dine to avoid Pneumocystis pneumonia.PPoliomyelitis and polioOLIOMYELITIS AND POLIO
Poliomyelitis is a contagious infectious disease that is caused
by three types of poliovirus. The virusescause damage and
destruction of cells in the nervous system. Paralysis can result
in about 2% of those who contract the disease, which is called
polio. Most people who contract polio either have mild symp-
toms or no symptoms at all.womi_P 5/7/03 11:09 AM Page 445