LUNG INFECTIONS
I. INFECTIONS
QUESTIONS TO CONSIDER AS LEARNING OBJECTIVES:
- The majority of bacterial pneumonias arise via the airways and are
known by this general term.
- The morbidity and mortality of any given bacterial pneumonia can
be reliably predicted based on these two general principles.
- A patient with high fever, shortness of breath and cough productive
of foul smelling, yellow-brown sputum has this disease until proven otherwise.
- Viral pneumonias can be distinguished morphologically from bacterial
pneumonias because they preferentially involve this "part" of
the lung tissue.
- Bacterial pneumonia in the elderly is commonly preceded by infection
with this type of organism.
- A localized collection of pus in the lung surrounded by a fibrous
capsule is referred to by this term.
- This ominous late systemic expression of bacterial pneumonia may
also precede pneumonia.
- Affectionately known in the past as "the old persons friend",
lobar pneumonia is readily cured with penicillin and is almost always caused
by this organism.
- These characteristic structures, seen within the nuclei and/or cytoplasm
of lung cells, may provide specific clues as to a pneumonia's etiology.
- Solidification of the lung, usually by bacterial pneumonia, is known
by this pathologic term.
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I. INFECTIONS
- Most of the organisms that cause infectious pneumonias come from
the air we breathe.
- Respiratory tract infections occur more commonly then infection
of any other organ system.
- Viruses and bacteria account for the majority of lung infections.
- Viral infection predisposes an individual to immediate bacterial
infection, primarily by damaging pulmonary defense mechanisms.
- Viruses need living cells in order to replicate and infect. Viral
lung infections are centered on the lung interstitium where the cells are.
- Bacteria are saprophytes. Bacterial infections evoke an exudative
cellular reaction primarily centered on the alveolar spaces. The process
leads to consolidation of the lung tissue.
- The two cardinal determinants of outcome in all infections are:
the virulence of the organism and the immune status of the host. Fortunately,
in industrialized countries, most healthy people never encounter an organism
sufficiently virulent to cause serious injury.
- Common viral organisms causing respiratory infections are influenza
A and B, respiratory syncytial virus (RSV), adenovirus, and rhinovirus.
- The most common cause of primary respiratory infection in otherwise
healthy individuals is the interstitial or "atypical" pneumonia
caused by Mycoplasma pneumoniae.
- The most common bacterial organisms causing pneumonia are staphylococci,
streptococci, pneumococci, Hemophilus influenzae, Pseudomonas aeruginosa
and the coliform bacteria.
- The clinical findings in patients with viral pneumonia are fever,
shortness of breath and non-productive cough.
- The clinical findings in patients with bacterial pneumonias are
high fever, shortness of breath, and productive cough with foul sputum.
There can be further complications.
- Bacterial pneumonias often result in lung tissue destruction.
- Once destroyed, lung tissue does not regenerate. Cavities filled
with dead tissue and pus may form in bacterial pneumonias that destroy
tissue.
- Such a cavity is referred to as an abscess.
- Once a bacterial pneumonia begins, seeding of the systemic circulation
with bacteria may occur. This phenomenon leads to sepsis.
- Most bacterial pneumonias begin where the organisms are first deposited
in the terminal airways. For this reason, patchy, multifocal bacterial
pneumonia is called bronchopneumonia.
- Mycobacteria, fungi and parasites may also infect the lungs of both
healthy and immunocompromised hosts.
- Mycobacteria and fungi tend to elicit granulomatous reactions in
response to the organism.
- Parasitic infections in healthy individuals are rare in the U.S.
A number of unusual parasites may prey on individuals who are immunocompromised.
- Bacterial pneumonias may organize if treated (or if they spontaneously
resolve. Some do!). Organization occurs as fibroblasts from the interstitium
of the alveolar wall migrate out into the alveolar spaces, contract and
produce collagen scar in variable amounts.
- Nosocomial infection.
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Outline
Go Back to Pulmonary
[ Anatomy, Embryology and Physiology
of the Lung | Edema, Embolism, Infarction, and
Pulmonary Hypertension | Lung Infections
| Adult Respiratory Distress Syndrome (ARDS) and
Chronic Interstitial Lung Disease | Airway Diseases
COPD | Lung Disease Caused by Inhaled Dust
| Lung Cancer ]
Questions?
Comments? Send a message to the CATS guru: jkessler@salus.uvm.edu