Pneumonia

Pneumonia is an inflammatory disease of the lungs, almost always caused by an infection, which disrupts the flow of oxygen and makes breathing very difficult.

Pneumonia is a severe and common illness, affecting about 1 in 100 people each year.

It can be caused by various microorganisms (such as viruses, bacteria, fungi, and protozoa), as well as by physical factors (like the aspiration of food or foreign objects) or chemical factors (such as the aspiration of hydrocarbons or the effects of certain drugs). Its severity ranges from mild to critical.

This disease is especially dangerous for children under five, the elderly, individuals with immune deficiencies, and populations with limited economic resources. In these cases, pneumonia can be fatal.

Pneumonia is typically classified into two major groups:

• Community-acquired pneumonia (CAP): This type is acquired outside of a hospital setting. Common examples include pneumococcal pneumonia and Mycoplasma pneumoniae.
• Hospital-acquired pneumonia (HAP) or nosocomial pneumonia: This form is generally more severe because patients’ immune defenses are often compromised, and the microorganisms causing it tend to be more resistant to antibiotic treatment.

Pneumonia is most commonly caused by viral and bacterial infections and is the leading cause of death in children under five worldwide.

In general, pneumonia can arise from two main types of causes:

1. Infectious causes
   • Bacterial pneumonias: Most cases of community-acquired pneumonia are due to Streptococcus pneumoniae (pneumococcus). However, other bacteria can also cause pneumonia, some with additional complications, including:
     • Mycoplasma pneumoniæ.
     • Haemophilus influenzae type b.
     • Streptococcus pyogenes.
     • Staphylococcus aureus.
     • Coxiella burnetti (Q fever).
     • Chlamidia psittachi (Psittacosis).
     • Klebsiella pneumoniæ.
     • Legionella pneumoniæ (Legionnaires' disease).
   • Viral pneumonias (pneumonitis). Many viruses can cause pneumonia, particularly in children aged one month to five years. The most common are respiratory syncytial virus (RSV) and rhinovirus. Other viruses include influenza, varicella-zoster, cytomegalovirus (CMV), and coronaviruses, including SARS-CoV-2 (COVID-19).
   • Parasitic pneumonia. The most severe form is caused by Pneumocystis carinii, which mainly affects individuals with HIV or other immunosuppressive conditions.
   • Fungal pneumonia: Rare and typically seen in people with weakened immune systems. One example is Cryptococcus infection, often affecting patients with HIV.
2. Non-infectious causes
   • Aspiration pneumonia: This occurs when gastric contents, foreign objects, or substances (e.g., hydrocarbons) enter the lungs, often due to accidental inhalation or in cases of impaired consciousness.
   • Interstitial lung diseases (ILD): In adults, this can manifest as pulmonary fibrosis, while in children, it can cause lung scarring. Causes are often unclear.
   • Radiation pneumonitis or drug-induced pneumonitis.
   • Hypersensitivity pneumonitis: Though not infectious, it involves a lung reaction to various substances (over 300 known triggers), which can vary widely between individuals. Some examples are:
     • Occupational and environmental lung diseases: Resulting from exposure to agricultural products, heavy metals, molds, algae, poorly ventilated buildings, pollution, etc.
     • Granulomatous pneumopathies: Occur in autoimmune conditions like Wegener's granulomatosis, sarcoidosis, and berylliosis.
     • Eosinophilic pneumonias: Includes acute pulmonary eosinophilia, which can be linked to toxins (e.g., cigarette smoke, cocaine, pollutants), Löeffler syndrome and chronic eosinophilic pneumonia of unknown origin.

The most common symptoms and signs of pneumonia include:

• Fever, chills and sweating.
• Productive cough, often with mucus that may be yellowish, salmon-colored, or purulent, depending on the causative microorganism.
• Chest pain that worsens with breathing or coughing.
• Headache.
• Muscle and joint pain.
• Loss of appetite, weakness, and general malaise.
• Dyspnea (difficulty breathing), in some cases.

Crackling sounds (rales) heard during lung auscultation in the affected area.

To diagnose pneumonia, the following tests may be performed:

• Physical examination: The doctor listens for crackling sounds (rales) in the affected lung area during auscultation.
• Chest X-ray: Shows characteristic signs of pneumonia and helps confirm the diagnosis.
• Cultures: Isolation of the causative microorganism from blood, sputum, or other tissues provides a definitive diagnosis.
• Serological and specific pathogen tests: Blood, urine, or secretion tests are used to detect specific pathogens, such as Legionella or SARS-CoV-2.
• Additional tests: Arterial blood gas (ABG) analysis measures oxygen and carbon dioxide levels in the blood, which can assess respiratory function. Chest CT scans may provide a clearer view of lung abnormalities. If pneumonia persists despite treatment, fiberoptic bronchoscopy (direct visualization of the bronchial tree with a flexible scope) may be needed.

If the person is in good general condition and does not have respiratory distress, home treatment is preferable to avoid additional hospital-acquired infections.

Treatment usually lasts at least ten days, with periodic medical check-ups to monitor for complications.

The recommended treatment includes:

• For bacterial pneumonia: Antibiotics are administered, with the choice, dose, and route of administration depending on the causative microorganism.
• For viral pneumonitis: Antibiotics are NOT effective; however, specific antiviral medications may be used for certain viral infections.
• Supportive care: For both outpatients and hospitalized patients, supportive measures include oxygen therapy, adequate hydration (oral or intravenous), and physical therapy to help expel secretions.
• In children: Oral zinc supplementation has shown benefits.
• For hospitalized patients: Those with severe pneumonia, especially those in the Intensive Care Unit (ICU), may require additional medications and treatments depending on their condition.

Vaccines that can help prevent pneumonia include:

• Measles vaccine: Included in the MMR vaccine (measles, mumps, rubella).
• Whooping cough (pertussis) vaccine: Administered to both children and pregnant women to reduce cases of childhood pneumonia.
• Haemophilus influenzae type b (Hib) vaccine.
• Pneumococcal vaccine.

With proper treatment, patients with acute, uncomplicated pneumonia typically recover within two to three weeks. However, severe complications can occur, particularly in elderly patients or those with underlying health conditions. The two most serious complications are:

• Acute respiratory failure (or cardiopulmonary failure).
• Empyema (accumulation of pus in the pleural cavity).