Pneumonia

Summary — نظرة عامة

Pneumonia is infection and inflammation of the lung parenchyma associated with infiltrates on chest X-ray. Children typically present with fever and signs of respiratory distress — tachypnea, subcostal retractions, cough, crackles, and decreased breath sounds.

Two rules anchor the entire topic: viruses are the most common cause of pneumonia in all age groups, and Streptococcus pneumoniae is the single most common bacterial pathogen after the neonatal period. The dominant organism otherwise shifts predictably with age, and that age band drives empiric antibiotic choice.

Etiology by Age Group

Empiric therapy in pediatric pneumonia is age-driven. Apply the Rule of 3 — commit the three highest-yield organisms in each band rather than memorizing exhaustive lists.

Beyond age, host factors also matter. Refer to the Risk Factors for Developing Pneumonia and Their Consequences for how impaired mucociliary clearance, CNS depression, and immunosuppression predispose to infection across all ages.

Viral Pneumonia

Pneumonia in children is most likely viral — the default assumption in an otherwise well-appearing child.

Clinical presentation: a prodrome of URI-type symptoms, followed by sudden-onset tachypnea, a nonproductive and frequently paroxysmal cough, and low-grade fever.

Chest X-ray: perihilar and parenchymal infiltrates.

Management: supportive — fluids and oxygen if necessary.

Bacterial Pneumonia

Streptococcus pneumoniae

S. pneumoniae are gram-positive diplococci and the most common bacterial cause after the neonatal period. Classic presentation: abrupt onset with high fever, chills, chest pain, dyspnea, and blood-tinged sputum.

Management:

• Outpatient: high-dose amoxicillin 80–100 mg/kg/day for 7–10 days.
• Inpatient: 2nd- or 3rd-generation cephalosporin.
• Penicillin-allergic: macrolide or cephalosporin.
• Macrolide resistance: vancomycin.

Complications: pleural effusion (up to 60% of cases) and empyema.

Staphylococcus aureus

S. aureus is much less common than pneumococcus and S. pyogenes, but it is a very serious and frequently fulminant cause. Infants with S. aureus pneumonia frequently develop pneumatoceles, abscesses, and empyema; the right lung is affected more often than the left, and blood cultures are frequently positive. Pneumatoceles are very common, appear 3–4 days into therapy, require no specific treatment, and resolve over time.

Management: hospitalization with nafcillin, or vancomycin if there is a high community prevalence of MRSA, recent hospitalization, an indwelling catheter, or tracheostomy. Empyema requires closed suction drainage.

Atypical Pneumonia

Atypical pneumonias usually occur in children > 5 years of age. Patients typically have no sputum production, a nontoxic appearance, and a normal or slightly elevated WBC count. They often follow an upper respiratory infection and may be caused by Mycoplasma, Chlamydia pneumoniae, Chlamydia psittaci (bird farmers), Legionella, Histoplasma, Coccidioides, and viruses.

Mycoplasma pneumoniae

M. pneumoniae is a common cause of community-acquired pneumonia in children > 5 years and adolescents. Incubation: 2–3 weeks. Classic presentation: a prodrome of headache, fever, and pharyngitis.
On chest X-ray the findings are worse than the clinical symptoms.

Extrapulmonary manifestations are a favourite exam target:

Diagnosis: definitive test is Mycoplasma IgM antibody; a positive cold agglutinin titer (present in ~50% of pneumonia cases) is suggestive.
Management: macrolide or doxycycline. Prognosis: recovery can be slow (> 6 weeks), and an asymptomatic carrier state may persist for weeks to months.

Chlamydia pneumoniae

C. pneumoniae causes epidemic pneumonia in older children and adolescents and accounts for ~10% of community-acquired pneumonias. It classically produces a biphasic illness: the patient first has a sore throat that is negative for group A Streptococcus, and pneumonia develops 2–3 weeks later.
Management: macrolide or tetracycline/doxycycline (avoid in children < 8 years).

Recurrent Pneumonia

Recurrent pneumonia is defined as > 2 episodes within 1 year or ≥ 3 episodes in any time frame, with radiographic clearing between episodes. The radiographic pattern points to the underlying problem.

Management: antibiotic therapy plus treatment of the underlying condition. Refer to the Risk Factors for Developing Pneumonia and Their Consequences for how impaired mucociliary clearance and immune defects set the stage for repeated infection.

Key Points for Exams — نقاط مهمة للامتحانات

• Viruses are the most common cause of pneumonia in all age groups; S. pneumoniae is the most common bacterial pathogen after the neonatal period.
• Age drives etiology (Rule of 3): < 3 months → GBS, Chlamydia trachomatis, RSV; 3 months–5 years → RSV, Parainfluenza, Adenovirus; > 6 years → S. pneumoniae, Mycoplasma, Chlamydia pneumoniae.
• S. pneumoniae: gram-positive diplococci, abrupt high fever with blood-tinged sputum; outpatient = high-dose amoxicillin 80–100 mg/kg/day; complications = pleural effusion (60%) and empyema.
• Pneumatoceles on CXR = S. aureus, usually the right lung; treat with nafcillin (vancomycin if MRSA risk); empyema needs closed suction drainage.
• Mycoplasma = "walking pneumonia": CXR worse than the exam; extrapulmonary HAPTENS; diagnose with IgM (cold agglutinins suggestive); treat with a macrolide or doxycycline.
• Chlamydia pneumoniae: classic biphasic illness — GAS-negative sore throat, then pneumonia 2–3 weeks later.
• Recurrent, same-location infiltrates = structural lesion (BB-SAF); dense infiltrates in different locations = recurrent bacterial infection from an underlying disorder (asthma, CF, PCD, immune dysfunction).