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Pneumonias: Symptoms, Classification, Causes, Morphology

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Pneumonias are infection and inflammation of lung parenchyma. The lungs parenchyma consist of a large number of thin-walled lungs’ air sac (alveoli).

Which is filled with pus or fluids, causing various symptoms including a cough (dry or wet), fever, chills and difficulty breathing, etc. 

Pneumonia is generally caused by bacterial so-called bacterial pneumonia. It can also be caused by various viruses such as Respiratory syncytial virus, coronavirus (COVID-19), Influenza virus, etc. 


Symptoms of Pneumonia

Pneumonia symptoms can vary from more common to less common symptoms. Which depends on the type of germ causing the infections in your body. They are the following symptoms;

Common Symptoms of Pneumonias Include:

  • A Cough: produce dry cough, or contains blood-stained mucus (Phlegm), or produces mucus with green, brown, yellow.
  • Rapid heart rate
  • Difficulty breathing: Rapid and shallow breathing, shortness of breath
  • High temperature in your body
  • Sweating and Shivering with fever
  • Loss of Appetite, low energy, and fatigue in your body
  • Chest pain (sharp or stabbing chest pain)

Less Common Symptoms of Pneumonia Include:

  • Haemoptysis (coughing with blood)
  • Headache 
  • Fatigue
  • Wheezing 
  • Muscle and joint pain
  • Confusion (generally in elder people)
  • Nausea and vomiting (generally in children)
  • Feeling sick


Classification of Pneumonias 

The classification of pneumonias based on etiology and anatomy of lung infection.

Etiological/ According to clinical setting:

  1. Community-Acquired Acute Pneumonia
  2. Community-Acquired Atypical Pneumonia
  3. Health Care-Associated Pneumonia
  4. Hospital-Acquired Pneumonia (Nosocomial Pneumonia)
  5. Chronic Pneumonia
  6. Aspiration Pneumonia
  7. Pneumonia with Immune Compromised Host
  8. Necrotizing Pneumonia and Lung Abscess

Anatomical classification 

  1. Bronchopneumonia
  2. Lobar pneumonia 


Causes of Pneumonia

Pneumonia causes are following such as bacteria, viruses, fungus, aspiration, in a hospital setting, etc. 

Bacterial causes:

  • Streptococcus pneumonia
  • Haemophilus influenzae
  • Moraxella catarrhalis
  • Staphylococcus aureus
  • Legionella pneumophila
  • Enterobacteriaceae (Klebsiella pneumonia, Serratia marcescens, etc) and Pseudomonas spp., etc.


  • Respiratory syncytial virus
  • Parainfluenza virus
  • Human metapneumovirus (it is most commonly in children)
  • Influenza virus A and B (it is most common in adults)
  • Adenovirus (Military recruits)
  • SARS virus 
  • Coronavirus (COVID-19), etc.

Fungal causes: It is a rare cause of pneumonia, some fungi are given below which possible causes pneumonia;

  • Histoplasma capsulatum
  • Blastomyces dermatitidis
  • Coccidioides immitis
  • Paracoccidioides brasiliensis
  • Sporothrix schenckii, etc

Aspiration pneumonia:

It is caused due to breathing in vomit (gastric contents), inhaled food, and a foreign substance such as a peanut, or a harmful substance (e.g. smoke or a chemical) mixed with

anaerobic oral flora (Bacteroides, Prevotella, Fusobacterium, etc) and aerobic bacteria (Streptococcus pneumoniae, Staph. Aureus, etc). 

Hospital setting (Nosocomial infection):

Pneumonia that develops in a patient admitted in hospital while being treated for other conditions or having an operation in hospital;

people present in the intensive care units on breathing machines are specifically at high risk of developing ventilator-associated pneumonia which is associated with bacteria such as

Staphylococcus aureus (usually methicillin resistance), Enterobacteriaceae ( Klebsiella spp., Escherichia coli, etc). 


Risk Groups 

There are the following groups that are highly at risk for developing pneumonia such as;

  • Elderly people
  • Babies and young child
  • People who smoke continuously
  • Other health diseases such as cystic fibrosis, asthma, or liver, kidney, and heart abnormalities
  • Those people have weakened immune systems:
    • For example, following conditions that cause weakened immune systems, they are following; having HIV/AIDS, recent infections like flu, having chemotherapy, etc.


Diagnosis of Pneumonias 

Pneumonia diagnosis is based on the fact that your doctor will ask many questions about taking a medical history, and different examinations such as physical examination, diagnostic tests, etc.

Medical history

Your doctor will ask you many questions about signs and symptoms presenting in your health, and how and when they began. They are following some possible queries such as;

  • A recent travel history
  • Occupational history 
  • Contact with animals
  • Exposure and contact with other sick people at school, home, etc.
  • Some other recent diseases such as asthma, cystic fibrosis, etc.

Physical examination 

Your doctor will be hearing your lungs sound with the help of a stethoscope. If you have pneumonia, your lungs may make some abnormalities such as bubbling, crackling, and rumbling sounds when you inhale air normally.

Diagnostic tests

If your doctor suspects that you may have pneumonias, they may recommend some tests that help to confirm the diagnosis and learn more details about your infection. These may include

  • Blood test
  • Chest X-ray
  • Pulse oximetry 
  • Sputum test

Some additional tests for hospitalized patients:

  • CT Scan
  • Arterial blood gas test
  • Pleural fluid culture
  • Bronchoscopy 


Complications of Pneumonia

Complications of pneumonia are generally more common in young children, elderly people, and those people with pre-existing health conditions, such as HIV/AIDS, diabetes, etc.

Some possible complications include:

  • A lungs abscess: It is due to tissue destruction and necrosis
  • Pleurisy 
  • Fibrosis: It is due to the organization of the intra-alveolar exudates. 
  • Empyema: It is due to suppurative material that may accumulate in the pleural cavity. 
  • Arthritis, meningitis, and endocarditis: It is due to bacterial dissemination.  
  • Sepsis (blood poisoning): It is a rare but serious complication


It is patchy exudative consolidation of your lung parenchyma-focal areas of palpable consolidation and that involves more than one lobe.

It is an acute neutrophilic suppurative exudation filling bronchi, bronchioles, and alveoli that eventually resolves. 

Morphology of Bronchopneumonia


  • Foci of consolidation in patches throughout one or several lobes
  • Frequently bilateral and basal
  • 3 or 4 cm in diameter, slightly elevated, gray-red to yellow
  • Pleural involvement is less common than other pneumonia called lobar pneumonia


  • Focal neutrophilic suppurative exudate that fills bronchi, bronchioles, and adjacent alveolar spaces
  • Ciliated epithelial is destroyed and vascular congestion. 


Lobar Pneumonia

Lobar pneumonia is contagious airspaces of part or all of a lobe that is homogeneously filled with exudative materials.

It is visualized on a radiograph as a lobar or segmental consolidation and it is usually unilateral

Morphology of Lobar pneumonia

There are four pathological stages of inflammation.

  1. Stage-I: Congestion
  2. Stage-II: Red Hepatization 
  3. Stage-III: Gray Hepatization
  4. Stage-IV: Resolution 



  • The lung is heavy, boggy, and dark red mass. 
  • An abundant frothy red fluid squeezed from it. 


  • The alveolar spaces are filled with inflammatory exudates and organisms.
  • Neutrophils are abundant, and fibrin will be present.

Red Hepatization


  • Lungs: red, firm, and airless
  • Liver like consistency 
  • Affected lung tissue sink in water.


  • Capillary engorgement 
  • Alveolar spaces are filled with neutrophils, red blood cells, and fibrin materials. 
  • If organism presents only a few.

Gray Hepatization


  • Fibrinous pleurisy will be present
  • The cut surface is dry, granules and gray 


  • Capillary engorgement resolved
  • Alveolar spaces are distended and filled with dense fibrin mass and with dead and dying polymorphs. 
  • It is a progressive degeneration of red cells that become gray color.



  • Firbinou or fibrinopurulent pleural exudate may resolve or undergo organization.
  • Leaving fibrous thickening or permanent adhesions.


  • Capillaries will be normal
  • Exudates within alveoli are
    • Enzymatically digested to produce granular materials, semifluid debris mass that is resorbed, and which is ingested by cells called macrophages, or coughed up.
    • Or organized by fibroblasts growing into it.



Treatment of Pneumonia

Pneumonia treatment is based on there condition present in your body either mild condition or severe condition, There are the following treatment methods given below

Mild pneumonia is generally treated at home by;

  • Take plenty of rest
  • Taking plenty of fluids
  • Taking a medication: If bacterial infection and if fever and pain are present then take painkillers such as paracetamol or ibuprofen.
  • If your symptoms are severe then you contact to hospital and take treatment. 


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