2. Bronchopneumonia – In this type, the pneumonia involves inflammation of both the larger airways (bronchi) and the smaller airways (bronchioles). The inflammation is generally more widespread (diffuse) and primarily affects smaller functional units of the lung called lobules.

3. Interstitial pneumonia – Here, the inflammation mainly affects the supporting tissue of the lung, known as the interstitium. This tissue surrounds the air sacs and blood vessels of the lungs.

3. Duration

This classification is based on how long the pneumonia lasts.

1. Acute pneumonia: This type of pneumonia has a shorter course, typically lasting only a few days and not extending beyond two weeks.

2. Chronic Pneumonia: This form of pneumonia persists for a longer period.

   • It lasts for more than two weeks.

   • It is more frequently seen in patients with weakened immune systems (Immune Suppressed patients).

   • Tuberculosis (TB) is a common cause of chronic pneumonia.

4. Clinical Grounds

This classification categorizes pneumonia based on the setting in which it was acquired or specific patient populations affected.

1. Community-acquired pneumonia (CAP):

   • CAP is diagnosed when a person develops pneumonia in their everyday environment (community setting) or within the first 48 hours after being admitted to a hospital. This timeframe suggests the infection was present before hospitalization.

   • Common causative agents include Streptococcus pneumoniae, Haemophilus influenzae, Legionella species, and Pseudomonas aeruginosa.

   • In individuals younger than 60 years old, pneumonia is the most frequent cause of CAP.

   • Viruses are the most common cause of pneumonia in babies and young children.

2. Hospital acquired (Nosocomial pneumonia):

   • Hospital Acquired Pneumonia (HAP), also known as nosocomial pneumonia, is defined as pneumonia that develops more than 48 hours after a patient is admitted to a hospital. This time frame indicates the infection was likely acquired within the hospital setting. Patients must not have shown signs of infection upon admission to be classified as having HAP.

   • HAP is considered a serious healthcare-associated infection. It is the most harmful type of nosocomial infection and is a leading cause of death in patients who develop such infections.

   • Common microorganisms responsible for HAP include Enterobacter species, Escherichia coli, influenza viruses, Klebsiella species, Proteus species, Serratia marcescens, Staphylococcus aureus, and Streptococcus pneumoniae.

3. Aspiration pneumonia:

   • Aspiration pneumonia occurs when substances from the upper airways, either produced by the body (endogenous) or from outside the body (exogenous), enter the lower airways and lungs.

   • The most frequent form of aspiration pneumonia is a bacterial infection resulting from inhaling bacteria that normally live in the upper respiratory tract.

   • Aspiration pneumonia can occur both in community settings and within hospitals.

   • Common pathogens involved are Streptococcus pneumoniae, Haemophilus influenzae, and Staphylococcus aureus.

4. Pneumonia in immunocompromised patients:

   • This category includes specific types of pneumonia that are more common or severe in individuals with weakened immune systems. Examples include Pneumocystis pneumonia, various fungal pneumonias, and pneumonia caused by Mycobacterium tuberculosis.

   • Patients with compromised immunity are more susceptible to developing pneumonia from organisms that typically do not cause disease in healthy individuals (organisms of low virulence).

   • It is important to note that pneumonia in immunocompromised patients can also be caused by the same organisms seen in HAP and CAP.

5. Primary or secondary pneumonia

   • 1. Primary pneumonia: This type of pneumonia develops in previously healthy individuals living in the community. It is often lobar pneumonia caused by Streptococcus pneumoniae.

   • 2. Secondary pneumonia: This type of pneumonia develops as a consequence of a pre-existing condition or situation. It can occur:

     • After a previous respiratory illness.

     • In individuals with weakened immune systems, such as those with AIDS.

     • Following a surgical operation, making it a risk for post-operative patients.

Pathophysiology of Pneumonia

This describes the sequence of biological events that occur in the body during the development of pneumonia.

When infectious agents reach the alveoli (the tiny air sacs in the lungs), they attach to the walls of the bronchi and bronchioles (the airways).

These agents then multiply outside of the cells (extracellularly), triggering an inflammatory response. This inflammation leads to the leakage of fluid and inflammatory cells (exudates) into the air spaces of the alveoli.

White blood cells (WBCs), the body’s defense cells, migrate to the alveoli to fight the infection. The alveoli become thickened and solid (consolidation) as they fill with this exudate.

Due to the inflammation, the affected areas of the lung are not adequately ventilated, meaning air cannot flow in and out properly. This is due to increased secretions and swelling (edema) in the airways.

This leads to a partial blockage (occlusion) of the alveoli and bronchi, causing a reduction in the amount of oxygen within the alveoli.

As a result, venous blood returning from the affected areas to the heart does not get fully oxygenated in the lungs.

This results in a lower than normal level of oxygen in the arterial blood (arterial hypoxemia). If the interference with gas exchange is severe enough, it can even lead to death.

Clinical Features of Pneumonia

These are the signs and symptoms that a person with pneumonia might experience.

• Fever with chills (Temperature 38-39°C): An elevated body temperature is a common sign of infection.

• Cough (may be absent in neonates and infants) with sputum production in older children: A cough, which may produce phlegm or mucus in older children, is a typical symptom. However, it may be absent in very young infants.

• Fast breathing (Tachypnea): An increased respiratory rate is a key indicator that the body is trying to compensate for reduced oxygen intake.

• Nasal flaring: (with inspiration, the side of the nostrils flares outwards): The widening of the nostrils during inhalation is a sign of increased effort to breathe.

• Chest indrawing: (it is inward movement of the lower chest wall when the child breathes in): This occurs when the muscles between the ribs are pulled inward during inhalation, indicating significant difficulty breathing.

• Altered consciousness: Changes in alertness or awareness can occur due to reduced oxygen levels in the brain.

• Irritability: Increased fussiness or agitation, especially in infants and young children.

• Shortness of breath: A subjective feeling of difficulty getting enough air.

• Grunting respirations: A short, guttural sound made during exhalation, indicating an attempt to keep the alveoli open.

• Chest in-drawing: (Repeated for emphasis).

• Stridor: A high-pitched, whistling sound during breathing, often indicating an upper airway obstruction, but can be present in some cases of pneumonia.

• Wheezing: A whistling or musical sound during breathing, indicating narrowed airways.

• Crackles: Also known as rales, these are popping or bubbling sounds heard during inhalation, indicating fluid in the small airways.

• Decreased breath sounds: When listening with a stethoscope, the intensity of breath sounds may be reduced over the affected area of the lung.

Diagnosis and Investigations

These are the methods used to confirm a diagnosis of pneumonia.

History taking. The process of diagnosing pneumonia often starts with gathering information about the patient’s medical history, paying particular attention to any recent respiratory tract infections.

Physical examination. A key part of the diagnostic process involves a physical examination. Specifically, the healthcare provider will assess the patient’s breathing rate (number of breaths per minute) and listen to their breath sounds using a stethoscope.

Chest x-ray. This imaging technique is crucial for confirming the diagnosis and assessing the extent of the pneumonia. It helps to identify the structural distribution of the infection, such as whether it is lobar (confined to a lobe) or bronchial (involving the airways). The chest x-ray can also reveal other features, such as multiple abscesses or infiltrates (seen more often with staphylococcus infections), empyema (pus in the space between the lung and the chest wall, also associated with staphylococcus), scattered or localized infiltration (common in bacterial pneumonia), or diffuse/extensive nodular infiltrates (more frequently seen in viral pneumonia). Interestingly, in cases of mycoplasma pneumonia, the chest x-ray may sometimes appear clear despite the presence of infection.