Lower respiratory tract infection refers to infection involving the airways below the larynx (bronchi, bronchioles, and lung parenchyma). The cardinal symptoms are cough, fever, tachypnea, and respiratory distress, though presentation varies with age and causative organism (Tintinalli's Emergency Medicine, p. 2717). Pneumonia, the most significant LRTI, is classified anatomically/radiologically into lobar pneumonia, bronchopneumonia (lobular pneumonia), and interstitial pneumonia, based on the pattern of alveolar/airway involvement (Fishman's Pulmonary Diseases and Disorders, p. 122-2137).

Patient: 58-year-old male, chronic alcoholic, non-smoker.

Presenting complaint: 3-day history of high-grade fever with chills, right-sided pleuritic chest pain, and cough productive of rusty (blood-tinged) sputum.

History: Sudden onset symptoms following a preceding upper respiratory viral illness. No prior lung disease. No recent hospitalization.

Diagnosis: Community-acquired lobar pneumonia (pneumococcal).

Pathophysiology: Organisms provoke inflammatory edema that spreads centrifugally within the alveoli via the pores of Kohn and canals of Lambert, filling an entire lobe fairly uniformly. Consolidation is nonsegmental (crosses segmental boundaries) but confined to one lobe; volume loss is minimal in the acute stage. A large lobar consolidation with pleural effusion strongly suggests a bacterial process (Fishman's Pulmonary Diseases, p. 122-2136).

Patient: 72-year-old female, known case of COPD, bedridden after a recent stroke.

Presenting complaint: 4-day history of low-grade fever, worsening cough with purulent sputum, and increasing breathlessness. No pleuritic pain.

History: Gradual onset, superimposed on chronic bronchitis. Poor oral intake, occasional choking on feeds (aspiration risk). No single dramatic onset as seen in lobar pneumonia.

Diagnosis: Bronchopneumonia (aspiration-associated, superimposed on COPD).

Pathophysiology: Infection begins in the bronchi/bronchioles, causing epithelial ulceration of the bronchial wall with fibrinopurulent exudate filling the surrounding peribronchiolar alveoli. This produces a segmental, patchy, multifocal distribution rather than uniform lobar filling; segments may become confluent over time. This pattern is typical of S. aureus, H. influenzae, post-viral CAP, and pneumonia complicating bronchiectasis or chronic bronchitis (Fishman's Pulmonary Diseases, p. 122-2137).

Both are managed with the general LRTI/CAP framework: assess severity (CURB-65), start empirical antibiotics promptly, provide supportive/respiratory care, and reassess with follow-up imaging if response is poor to rule out complications (effusion, abscess, empyema).

A 2025 systematic review and meta-analysis on complicated CAP in children (PMID: 41222098) and a 2025 review on antimicrobial stewardship in hospitalized CAP (PMID: 40202602) are current and do not contradict the classic diagnostic framework above, but reflect ongoing refinement of antibiotic duration/de-escalation strategies - worth checking if you need the latest antibiotic-stewardship specifics for a written case study.

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Pneumonia is the leading cause of death in children under 5 globally, with an estimated 120 million cases and about 1.3 million deaths annually; children under 2 years account for 81% of pediatric pneumonia deaths (Tintinalli's Emergency Medicine, p. 2705). Viruses cause over 70% of hospitalized pediatric pneumonia cases, though bacterial, atypical, and mixed infections are important, especially in severe or lobar presentations.

Patient: 18-month-old male infant.

Presenting complaint: 3-day history of runny nose and cough, followed by fever (38.8°C), fast breathing, and poor feeding.

History: Preceding upper respiratory viral illness. Attends daycare. Immunizations up to date (received PCV). No prior wheeze/asthma history. Mother reports the child is "breathing fast" and "chest is pulling in."

WHO/IMNCI classification: "Severe pneumonia" if chest indrawing present, or "Pneumonia (not severe)" if only fast breathing without chest indrawing (Park's Textbook of Preventive and Social Medicine, p. 189-190). Danger signs mandating urgent hospital referral ("very severe disease") include: not able to drink, convulsions, abnormal sleepiness/difficult to wake, stridor in a calm child, or severe malnutrition.

Diagnosis: Viral bronchopneumonia (post-viral, patchy bilateral pattern), mild-moderate severity.

Patient: 6-year-old female, previously healthy, fully immunized (including PCV13).

Presenting complaint: Sudden onset high fever (40°C) with rigors, right-sided chest/abdominal pain, and cough for 1 day. Mother reports the child "suddenly became very sick."

History: Abrupt onset (classic for lobar pneumonia, unlike the gradual bronchopneumonic pattern). No preceding prolonged coryza. School-aged children are more often affected by S. pneumoniae and Mycoplasma pneumoniae than infants (Tintinalli's Emergency Medicine, "Age-Specific Causes of Pneumonia," children 2-5 years and school-age).

Diagnosis: Lobar pneumonia, likely pneumococcal.

A 2025 systematic review/network meta-analysis (PMID: 41371717) evaluated diagnostic accuracy of imaging modalities (chest X-ray, CT, lung ultrasound) in pediatric pneumonia, and a 2024 meta-analysis (PMID: 39239917) found lung ultrasound has comparable or superior accuracy to chest radiography for diagnosing pediatric CAP, with the added benefit of no radiation - this is increasingly relevant for point-of-care diagnosis in children and may supplement or replace routine chest X-ray in some settings. A 2024 study (PMID: 39189186) also examined how often radiographic pneumonia is found in children presenting with wheeze, relevant to distinguishing bronchopneumonia/viral LRTI from reactive airway disease.

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