Pneumonia

Age-related evolution of pathogens

The etiological structure of community-acquired pneumonia is strictly tied to the child's age, which determines the rationale for the empirical prescription of antibiotics. A clear shift in flora can be observed throughout the course of the disease:

• Neonates: Intestinal bacteria and maternal birth canal flora dominate (Streptococcus agalactiae, Escherichia coli, Staphylococcus aureus). Pneumococcus is extremely rare.
• From 1 to 3 months: Transitional stage. The significance of neonatal flora decreases, while the role of Streptococcus pneumoniae increases. Chlamydia trachomatis acts as a specific pathogen.
• From 4 months to 4 years: In the vast majority of cases, typical bacterial flora prevails, with Streptococcus pneumoniae being the undisputed leader. The proportion of atypical pathogens is negligible.
• From 5 to 18 years: Intracellular pathogens come to the forefront (Mycoplasma pneumoniae, Chlamydophila pneumoniae), although pneumococcus maintains its position as one of the main pathogens.

Pathogenesis and exudate formation

The primary route of infection entry into the lower respiratory tract is considered to be aspiration of nasopharyngeal secretions. Microaspiration is physiological and occurs in half of healthy individuals, but the disease develops only when local defense mechanisms (cough reflex, mucociliary clearance) are depleted.

A preceding viral infection often creates a favorable background. The pathogen attaches to the epithelium of the bronchioles and alveoli, and begins to actively multiply. The released toxins increase capillary permeability. Initially, serous effusion accumulates in the alveoli. As the inflammation progresses, it is replaced by fibrinous exudate, leading to tissue consolidation. A sharp decrease in the aeration of the parenchyma impairs gas perfusion, provoking hypoxemia, hypercapnia, and respiratory acidosis.

Clinical and radiological diagnostics

The classical course of pneumonia begins acutely with intoxication syndrome, fever with chills, cough, and tachypnea. Local physical signs (dullness to percussion, bronchial breathing, crepitation, or moist rales) are detected in only 50–70% of patients.

The "gold standard" of diagnostics remains chest radiography. The diagnosis is considered reliable if the radiological sign of infiltration is combined with at least two of the four criteria:

1. Persistent fever (> 38 °C) for more than three days.
2. Cough with sputum.
3. Specific local physical changes.
4. Pronounced leukocytosis (above 15 × 10⁹/L) or a left shift in the formula (> 10% band neutrophils).

Principles of antibacterial therapy

Antibiotics are prescribed immediately upon confirmation of the diagnosis. About 80% of children with community-acquired forms are treated outpatients. In severe cases, step-down therapy is used: starting with parenteral administration followed by transition to the oral route.

Empirical drug selection:

• Children under 3 months: Combination of cefotaxime with ampicillin, or inhibitor-protected penicillins with aminoglycosides.
• Children older than 3 months (uncomplicated history): Drug of choice is amoxicillin, which covers the spectrum of pneumococcus.
• Risk factors (background diseases, recent antibiotic use): Amoxicillin/clavulanic acid.
• Suspicion of atypical flora or allergy to penicillins: Macrolides (azithromycin, clarithromycin).

Class and exam questions

What else to study on this topic

• Specifics of nosocomial and ventilator-associated pneumonia
• Morphological classification (focal, lobar, interstitial)
• Pathophysiology of respiratory acidosis and hypoxemia in inflammation
• Indications for hospitalization of young children
• Complications: pleurisy, abscesses, and infectious-toxic shock

Other topics in "Chapter 4. Respiratory Diseases"

Prepared by WhiteCoat Pro faculty in accordance with the medical school curriculum. For educational purposes only.