Pneumonia

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• Pneumonia is a common disease because:

1. The epithelial surfaces of the lung are constantly exposed to

many liters of air containing various levels of microbial

contaminants.

2. Nasopharyngeal flora are regularly aspirated during sleep, even

by healthy persons.

3. Other common lung diseases render the lung parenchyma

vulnerable to virulent organisms.

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• Pneumonia can be very broadly defined as any infection in the

lung.

• The clinical presentation may be as an acute, fulminant or a

chronic disease

• Acute bacterial pneumonias can manifest as one of two

anatomic and radiographic patterns, referred to as

bronchopneumonia and lobar pneumonia.

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• Bronchopneumonia implies a patchy distribution of

inflammation that generally involves more than one lobe.

• This pattern results from an initial infection of the bronchi and

bronchioles with extension into the adjacent alveoli.

• By contrast, in lobar pneumonia the contiguous air spaces of

part or all of a lobe are homogeneously filled with an exudate.

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• The anatomic distinction between lobar pneumonia and

bronchopneumonia can often become blurry, because:

(1) many organisms cause infections that can manifest with

either of the two patterns of distribution.

(2) confluent bronchopneumonia can be hard to distinguish

radiologically from lobar pneumonia.

• Therefore, it is best to classify pneumonias either by the specific

etiologic agent or, if no pathogen can be isolated, by the clinical

setting in which infection occurs.

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* Classification of pneumonia: 1. Community-Acquired Acute Pneumonia:– Streptococcus pneumonia

– Haemophilus influenza pneumonia

– Staphylococcus aureus pneumonia

– Legionella pneumophila pneumonia

2. Community-Acquired Atypical Pneumonia:– Mycoplasma pneumonia

– Viral pneumonia: Respiratory syncytial virus, para-influenza virus (children); influenza A and B (adults); adenovirus.

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3. Nosocomial Pneumonia.

4. Aspiration Pneumonia.

5. Chronic Pneumonia.• Granulomatous: Mycobacterium tuberculosis and

atypical mycobacteria.• Nocardia.• Actinomyces.• Histoplasma capsulatum.

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Community-Acquired Acute Pneumonias

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• Most community-acquired acute pneumonias are bacterial in

origin. However, may follow upper respiratory tract viral

infection.

• The onset is usually abrupt, with high fever, shaking chills,

pleuritic chest pain, and a productive mucopurulent cough.

• S. pneumonia (i.e., the pneumococcus) is the most common

cause of community-acquired acute pneumonia.

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Streptococcus (Pneumococcal ) pneumonia

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* Risk factors:

1. Patients with chronic diseases such as congestive heart failure, COPD, or

diabetes.

2. Patients with congenital or acquired immunoglobulin defects (e.g. AIDS).

3. Patients with decreased or absent splenic function (e.g. sickle cell

disease or after splenectomy).

- In the last group, such infections are more likely because the spleen

contains the largest collection of phagocytes and is therefore the major

organ responsible for removing pneumococci from the blood. The spleen is

also an important organ for production of antibodies against encapsulated

bacteria.

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* Morphology:• Both patterns of pneumonia, lobar or bronchopneumonia, may

occur.

• In lobar pneumonia pattern, the lower lobes or the right middle

lobe is most frequently involved because lung infection usually is

acquired by aspiration of pharyngeal flora (20% of adults harbor

S. pneumonia in the throat).

• In the era before antibiotics, pneumococcal pneumonia involved

entire lung lobe and evolved through four stages: congestion,

red hepatization, gray hepatization, and resolution. Early

antibiotic therapy alters or halts this typical progression.

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- In stage of congestion (1st day): the affected lobe is heavy and

red. The alveolar capillaries are congested and the alveoli show

exudate, scattered neutrophils, and many bacteria.

- In the stage of red hepatization (2nd – 4th day): the lung lobe has

a liver-like consistency; the alveolar spaces are packed with

neutrophils, red cells, and fibrin.

- In the stage of gray hepatization (5th – 8th day): the lung is dry,

gray, and firm, because the red cells are lysed, while the exudate

persists within the alveoli.

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- In the stage of resolution: occurs in uncomplicated cases, as

exudates within the alveoli are enzymatically digested to

produce granular, semifluid debris that is resorbed, ingested by

macrophages, coughed up, or organized by fibroblasts growing

into it).

- The pleural reaction (fibrinous or fibrinopurulent pleuritis) may

similarly resolve or undergo organization, leaving fibrous

thickening or permanent adhesions.

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Gross view of lobar pneumonia with gray hepatization.

The lower lobe is uniformly consolidated.

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Lobar pneumonia

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• In the bronchopneumonic pattern, foci of inflammatory

consolidation are distributed in patches throughout one or

several lobes, most frequently bilateral and basal. confluence

of these foci may occur in severe cases, producing the

appearance of a lobar consolidation.

• Pleural involvement is less common than in lobar pneumonia.

• Histologically, the reaction consists of focal suppurative

exudate that fills the bronchi, bronchioles, and adjacent

alveolar spaces.

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Bronchopneumonia

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Bronchopneumonia

20Bronchopneumonia

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* Clinical course of strept. (pneumococcal pneumonia):

• With appropriate therapy, complete restitution of the lung is the rule

for both forms of pneumococcal pneumonia, but in occasional cases

complications may occur like;

1. lung abscess formation;

2. Empyema (suppurative material may accumulate in the pleural cavity.

3. Lung fibrosis: due to organization of the intra-alveolar fibrinopurulent

exudate.

4. Bacteremic blood dissemination: may lead to meningitis, arthritis, or

infective endocarditis.

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Haemophilus influenza pneumonia

• Affects children, often after a respiratory viral infection and

adults having chronic pulmonary diseases such as chronic

bronchitis, cystic fibrosis, and bronchiectasis.

• H. influenza is the most common bacterial cause of acute

exacerbation of COPD.

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Staphylococcus aureus pneumonia• S. aureus is an important cause of secondary bacterial

pneumonia in children and healthy adults after viral respiratory

illnesses (e.g., measles in children and influenza in both

children and adults).

• Staphylococcal pneumonia is associated with a high incidence

of complications, such as lung abscess and empyema.

• Staphylococcal pneumonia occurring in association with right-

sided staphylococcal endocarditis is a serious complication of

intravenous drug abuse.

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Klebsiella pneumoniae

• K. pneumoniae is the most frequent cause of gram

negative bacterial pneumonia.

• Klebsiella-related pneumonia frequently afflicts debilitated

and malnourished persons, particularly chronic alcoholics.

• Thick and gelatinous sputum is characteristic, because the

organism produces an abundant viscid capsular

polysaccharide, which the patient may have difficulty

coughing up.

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Pseudomonas aeruginosa• Pseudomonas pneumonia is common in persons who are

neutropenic, usually secondary to chemotherapy; in victims of

extensive burns; and in patients requiring mechanical

ventilation.

• P. aeruginosa has a propensity to invade blood vessels at the site

of infection, with consequent extra-pulmonary spread;

Pseudomonas bacteremia is a fulminant disease, with death

often occurring within a matter of days.

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Legionella pneumophila pneumonia• L. pneumophila flourishes in artificial aquatic environments,

such as water-cooling towers and within the tubing system

of domestic (potable) water supplies. The mode of

transmission is thought to be either inhalation of aerosolized

organisms or aspiration of contaminated drinking water.

• Legionella pneumonia is common in persons with some

predisposing condition such as cardiac, renal, immunologic,

or hematologic disease. Organ transplant recipients are

particularly susceptible.

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Community-Acquired Atypical Pneumonias

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• The designation atypical denotes the moderate amounts of

sputum, absence of physical findings of consolidation, only

moderate elevation of white cell count, and lack of alveolar

exudates. Atypical pneumonia is caused by a variety of

organisms:

1. Bacterial: Mycoplasma pneumonia being the most common

cause.

2. Viral: influenza types A and B, the respiratory syncytial virus,

adenovirus, rhinoviruses, rubeola virus, and varicella virus.

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• Mycoplasma infections are particularly common among

children and young adults. They occur sporadically or as local

epidemics in closed communities (schools, military camps,

prisons).

• Microscopically: interstitial inflammatory reaction with

necrosis of the lining alveolar cells and minimal accumulation

of exudate inside the alveoli is the hallmark of atypical

pneumonia.

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Atypical pneumonia. The thickened alveolar walls are infiltratedwith lymphocytes and some plasma cells, with occasional alveolar edema in the center.

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Hospital-Acquired (Nosocomial) Pneumonias

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• Nosocomial, or hospital-acquired pneumonias are defined as pulmonary

infections acquired in the course of a hospital stay.

• Nosocomial infections are common in hospitalized persons with severe

underlying disease, those who are immunosuppressed, or those on

prolonged antibiotic regimens.

• Those on mechanical ventilation represent a particularly high-risk

group, and infections acquired in this setting are given the distinctive

designation ventilator-associated pneumonia.

* Causative agents:

1. Gram-negative rods (Enterobacteriaceae and Pseudomonas spp.)

2. Staph. aureus.

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Aspiration Pneumonia• Aspiration pneumonia occurs in debilitated patients or those who

aspirate gastric contents either while unconscious (e.g., after a

stroke) or during repeated vomiting.

• These patients have abnormal gag and swallowing reflexes that

facilitate aspiration. The resultant pneumonia is partly chemical,

resulting from the extremely irritating effects of the gastric acid,

and partly bacterial.

• This type of pneumonia is often necrotizing, pursues a fulminant

clinical course, and is a frequent cause of death in persons

predisposed to aspiration.

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Chronic Pneumonias• There is typically granulomatous inflammation, which may be

due to bacteria (e.g., M. tuberculosis) or fungi. Tuberculosis is

by far the most important entity within the spectrum of chronic

pneumonias;

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Thanks