= Solution
\b[In infants, <pneumonia> often has a patchy airway-centred pattern and less typical localizing symptoms, while collapse and systemic illness complicate its recognition.] The classical comparison is with an adult's acute <lobar pneumonia>, but age does not impose an absolute anatomical division.
The adult reference pattern is relatively continuous consolidation of a lobe. In the traditional pathological sequence, <congestion> is followed by red <hepatization>, with <red blood cells>, <neutrophils> and <fibrin> in the <alveoli>; later breakdown of the <red blood cells> contributes to grey <hepatization>, followed by clearance or organization. These stages are a descriptive model, can overlap, and are not a mandatory timetable for every adult infection.<Pneumonia Pathology in StatPearls>[Histopathology, lobar pneumonia and the four classical stages]{ref}
By comparison, an infant may have <bronchopneumonia>: separate foci centred on small <bronchi> and <bronchioles>, extending into adjacent <alveoli>, sometimes in both <lungs>. Airway secretions and inflammatory material coexist with patches of <atelectasis>; lesions of different ages can be present together. Coalescent foci can eventually resemble a larger area of consolidation. The distinction is anatomical rather than proof of one specific infecting organism.<Pulmonary Infections in the Normal Host>[Bronchopneumonia, Pathologic Features, airway-centred exudation and coalescence]{ref}
Question 8 supplies an essential historical qualification: some lesions labelled infantile “lobular pneumonia” were actually collapse. Distinguishing <atelectasis> from inflammatory <exudate> prevents that diagnostic inflation. The two conditions can nevertheless coexist.<Lectures on the Diseases of Infancy and Childhood (review, 1855)>[pp. 111–112, secondary collapse formerly described as lobular pneumonia]{ref}
Clinically, an infant cannot report pleuritic chest pain and usually swallows rather than expectorates sputum. The adult combination of rigors, chest pain and conspicuous rusty sputum is therefore a poor required checklist. More useful infant signs include rapid <breathing>, lower chest indrawing, nasal flaring, grunting, poor feeding, reduced activity and sometimes <cyanosis>. <Fever> can be present, but the youngest infants may instead show temperature instability and nonspecific illness. Physical signs can be scattered when the lesions are scattered; absence of one large area of dullness does not exclude <pneumonia>.<Pneumonia: Symptoms by the National Heart, Lung, and Blood Institute>[Infant symptoms and signs of breathing difficulty]{ref}<Neonatal Pneumonia by Merck Manual Professional Edition>[Symptoms and Signs, respiratory distress and temperature instability]{ref}
In current practice, the age group also changes the differential. Early neonatal <pneumonia> can be part of generalized <sepsis> acquired around birth; later infant infections include both viral and bacterial causes. Assessment integrates the illness history, <oxygen saturation>, examination and selected laboratory or imaging evidence rather than assigning a diagnosis from age alone. A positive airway culture can reflect colonization, so the organism must be interpreted with the clinical and inflammatory evidence.<Neonatal Pneumonia by Merck Manual Professional Edition>[Etiology; Diagnosis, blood cultures, tracheal aspirates and colonization]{ref}
The decisive comparison is therefore \b[patchy and mixed pathology, greater diagnostic difficulty, and frequent systemic presentation in infancy], with <lobar pneumonia> possible in children and <bronchopneumonia> possible in adults.
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