- Pulmonology
- Clinicals
Pneumonia: Types,Causes, Symptom, Diagnosis and Treatment
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- Revised on: 2020-06-30
Pneumonia is a respiratory disorder that involves an inflammation of the lung parenchymal structures, such as the alveoli and bronchioles resulting in an altered gaseous exchange.
Pneumonia is caused by infectious agents such as bacteria ,fungi and viruses and noninfectious agents such as gastric secretions that are aspirated into the lungs or inhalation of volatile or irritating substances.
Causes of pneumonia
Pneumonia is caused by infectious agents such as bacteria ,fungi and viruses and noninfectious agents such as gastric secretions that are aspirated into the lungs or inhalation of volatile or irritating substances.
The most common cause of community-acquired pneumonia in all groups is S. pneumoniae when an actual cause is identified
viruses have been found to be the most common cause in children less than 5 years of age.
Strep pneumoniae is the leading cause of subsequent infections.
On the other hand, Gram negative bacilli like Eschelicia coli and Enterobactericiae are the predorminant causes of Hospital-acquired or ventilator-associated pneumonia.
Classification and types of pneumonia
Pneumonias can be commonly classified according the setting in which they occur, the type of agent causing the infection, and distribution of the infection or pattern of lung involvement.
These pneumonias are classified based on;
1.Depending on the pattern of lung involvement.
It can be categorized depending on pattern of lung involvement into the following categories;
- Lobar pneumonia,
- Bronchopneumonia,
- Intestitial pneumonia and,
- Miliary pneumonia.
Acute bacterial pneumonias can be classified as lobar pneumonia or bronchopneumonia.
Lobar pneumonia is a form of exudative inflammationor a consolidation that affects a whole lobe or large portion of a lobe.
Bronchopneumonia is a suppurative inflammation or a patchy consolidation that affects one or more lobes in a multifocal or patchy manner.
Interstitial pneumonia, which is a diffuse inflammation that mainly involves the alveolar walls and bronchial tree connective tissue known as interstitium.
Miliary pneumonia is a less common type of pneumonia compared with the later, it occurs as a result of haematogenous spread and presents as numerous small, diffuse lesions throughout both lungs.
2.Setting in which pneumonia is acquired
Pneumonia can also be classifed by the setting associated with its development.
In this classification there are three main categories;
- Community-acquired pneumonia.
- Hospital-acquired pneumonia,
- Health care–associated pneumonia
Hospital-acquired pneumonia is a type that develops as a result of exposure to a pathogen within a hospital. This type is also known as nosocomial pneumonia, meaning its spread within the hospital facility.
This type is the one that was not present or incubating on admission to the hospital. Usually, infections occurring 48 hours or more after admission are considered hospital acquired.
Most of the causative bacterial present in the hospital include Pseudomonas aeruginosa, S. aureus, Enterobacter, Klebsiella pneumoniae, and Escherichia coli.
Its important to note that the bacteria responsible for hospital-acquired pneumonias are different from those responsible for community-acquired pneumonias, and many of them have acquired antibiotic resistance and are more difficult to treat.
Health care–associated pneumonia develops as a result of exposure to a microorganism from an healthcare facility, outpatient clinic or dialysis unit.
Lastly,community-acquired pneumonia is as an infection that begins outside the hospital or is diagnosed within 48 hours after admission to the hospital in a person who has not resided in a long-term care facility for 14 days or more before admission.
Community-acquired pneumonia can be bacterial or viral. S. pneumoniae is the most common bacterial cause while influenza virus, respiratory syncytial virus, adenovirus, and parainfluenza virus are the most common viral causes.
Sometimes health care–associated pneumonia may be classified as a subcategory of hospital-acquired pneumonia.
2.Causative organism
Pneumonia cal also be classified to other two types;Typical pneumonias and atypical pneumonias.
Typical pneumonias result from infection by bacteria that multiply extracellularly in the alveoli causing an inflammation and exudation of fluid into the air-filled spaces of the alveoli.
On the other hand atypical pneumonias are caused by viral and mycoplasma infections that invade the alveolar septum and the interstitium of the lung. This type produces less striking features than bacterial pneumonia because they lack of alveolar infiltration and purulent sputum, leukocytosis, and lobar consolidation on the radiograph. Features which are more pronounced in typical pneumonias.
Pneumonia can also be classified depending on the causative organism into the following classes
- Bacterial pneumonia
- Viral pneumonia
- Fungal pneumonia
Other types of pneumonia
Pneumococcal Pneumonia. S. pneumoniae (pneumococcus) remains the most common cause of bacterial pneumonia.
Pneumoniae is a gram-positive diplococcus, possessing a capsule of polysaccharide.
The virulence of the pneumococcus is a function of its capsule, which prevents or delays digestion by phagocytes. The polysaccharide is an antigen that primarily elicits a B-cell response with antibody production.
In the absence of antibody, clearance of the pneumococci from the body relies on the reticuloendothelial system, with the macrophages in the spleen playing a major role in elimination of the organism.
This, along with the spleen’s role in antibody generation, increases the risk for pneumococcal bacteremia in persons who are anatomically or functionally asplenic, such as children with sickle cell disease.
Opportunistic pneumonia is another type of inflammatory lung disease caused by microorganisms that are generally harmless to immunocompetent individuals. However, they can induce pneumonia in immunosuppresed patients such as those who have undergone bone marrow or organ transplantation, persons with cancers, and those on corticosteroid and other immunosuppressant drugs.
A fulminant pneumonia usually is caused by bacterial infection, whereas an insidious onset usually is indicative of a viral, fungal, protozoal, or mycobacterial infection.
Ventilator-associated pneumonia is common in the intensive care setting where critically ill individuals are receiving assisted ventilation. Ventilator-associated pneumonia is pneumonia that develops in mechanically ventilated patients more than 48 hours after intubation.
Invasive ventilation bypasses all the upper airway respiratory defences and exposes a person to potentially pathogen-inoculated respiratory equipment.
Aspiration pneumonia is common in aged-care settings and in people who have dysphagia or reduced level of consciousness.
When gastric secretions colonized with pathogenic bacteria are refluxed into the oropharynx and the cough and gag reflexes are diminished, the secretions can be inhaled into the larynx and lower respiratory tract.
The lobes on the right side are commonly affected because the right main bronchus is more vertical in orientation, branches first making it shorter, and has a slightly larger lumen than the left main bronchus.
The right bronchial branches usually service the middle and lower lobes therefore making these two loves most susceptible. Pneumonitis because of chemical injury from the acidic gastric contents reflux may worsen it.
Cryptogenic-organising pneumonia is a type of idiopathic interstitial pneumonia previously known as bronchiolitis obliterans–organising pneumonia.
Cryptogenic-organising pneumonia causes patchy subpleural and peribronchial consolidation, and intraluminal polyps.
Legionnaire disease is a type of bronchopneumonia that is caused by a gram-negative rod known as Legionella pneumophila. It occurs when water that contains the microorganism is aerosolized inhaled or aspirated by a susceptible person. It is characterized by presence of pneumonia along with diarrhea, hyponatremia, and confusion.
Predisposing factors to pneumonia
A number of factors can contribute to the development of pneumonia and these include
- Altered state or of consciousness such as in the cases of; Anaesthesia, Head injury, Cerebrovascular accident, Seizure disorder, Drug overdose, Alcohol intoxication,
- Neuromuscular dysfunct
