Community-acquired lower respiratory tract infection
Pneumonia
An acute infection of the pulmonary parenchyma that produces inflammation within the alveoli and surrounding lung tissue, potentially impairing ventilation and gas exchange.
Clinical vignette
A child with fever, cough, and focal lung findings
A previously healthy 4-year-old presents with 3 days of fever, cough, decreased appetite, and progressively faster breathing. Temperature is 39.2°C, respiratory rate is 44 breaths/minute, and oxygen saturation is 95% on room air.
The child is alert, drinking small amounts, and has mild subcostal retractions. Auscultation reveals focal crackles and decreased breath sounds over the right lower lung field.
Your first clinical task
Assess illness severity and determine whether this child can be treated safely as an outpatient while considering viral, typical bacterial, and atypical causes of pneumonia.
Anatomy & Localization
Pneumonia involves the distal airways and gas-exchanging lung
Localize the infection to the lung parenchyma and understand how extension into adjacent structures produces complications.
Pneumonia primarily involves the distal airways, alveoli, and pulmonary interstitium. In bacterial pneumonia, inflammatory material may fill alveolar spaces and produce consolidation. Viral infections more commonly create diffuse or patchy inflammation, although clinical and radiographic patterns frequently overlap.
Alveoli
Inflammatory cells, protein-rich fluid, and cellular debris may replace air within affected alveoli.
Interstitium
Inflammation may involve the supporting tissue surrounding alveoli and small airways.
Pleural space
Extension beyond the lung parenchyma may produce a parapneumonic effusion or empyema.
Pathophysiology
Infection triggers inflammation, alveolar filling, and impaired gas exchange
Follow the progression from pathogen entry to inflammatory injury and understand how viral, typical bacterial, and atypical pneumonia can overlap clinically.
Pneumonia develops when a pathogen reaches the lower respiratory tract and overcomes normal host defenses, including mucociliary clearance, cough, airway immune responses, and alveolar macrophages.
Pathophysiologic cascade
The bedside findings of pneumonia follow from inflammation and impaired ventilation of affected lung.
Pathogen reaches the distal lung
Viruses or bacteria enter the lower respiratory tract and overcome local airway and alveolar host defenses.
The inflammatory response begins
Resident immune cells recognize infection and recruit additional inflammatory cells, producing local edema and inflammatory injury.
Air spaces become poorly ventilated
Inflammatory cells, fluid, and cellular debris can accumulate within affected alveoli. In bacterial pneumonia, extensive alveolar filling may produce consolidation.
Gas exchange becomes impaired
Perfusion of poorly ventilated lung creates ventilation-perfusion mismatch, contributing to hypoxemia, tachypnea, and increased work of breathing.
Etiologic patterns
These patterns can guide clinical reasoning, but substantial overlap prevents reliable determination of etiology from any single clinical or radiographic feature.
Viral
- • Often affects younger children
- • May produce diffuse or patchy inflammation
- • Frequently accompanied by upper respiratory symptoms
- • Antibiotics do not treat the viral infection
Typical bacterial
- • Streptococcus pneumoniae is the most common bacterial cause
- • May present with abrupt fever and focal findings
- • Can produce alveolar consolidation
- • May progress to pleural complications
Atypical
- • More common in school-aged children and adolescents
- • Often associated with persistent cough
- • Mycoplasma pneumoniae and Chlamydia pneumoniae are common considerations
- • Clinical findings may be more diffuse
History & Physical
Assess the child before trying to name the pathogen
Severity is driven by respiratory status, oxygenation, hydration, perfusion, mental status, and the overall clinical trajectory.
1. Does this fit pneumonia?
- • Fever and cough: onset, duration, and progression
- • Tachypnea or increasing work of breathing
- • Chest pain or exercise intolerance
- • Focal crackles, bronchial breath sounds, or decreased air entry
- • Remember that lower lobe disease may present with abdominal pain
2. How sick is the child?
- • General appearance and interaction
- • Respiratory rate measured while calm
- • Pulse oximetry
- • Retractions, nasal flaring, grunting, or head bobbing
- • Oral intake, urine output, and hydration
- • Perfusion and mental status
3. What changes the risk?
- • Age and immunization status
- • Recent viral illness or sick contacts
- • Recent antibiotics or hospitalization
- • Aspiration risk or neurologic impairment
- • Tuberculosis exposure or relevant travel
- • Underlying cardiac, pulmonary, or immune disease
4. Could this already be complicated?
- • Significant or worsening respiratory distress
- • Markedly asymmetric or decreased breath sounds
- • Pleuritic chest pain
- • Persistent fever or worsening after initial improvement
- • Toxic appearance, poor perfusion, or altered mental status
Do not rely on auscultation alone
Etiologic clues
Age and clinical pattern can influence the differential, but substantial overlap means no single symptom, examination finding, or radiographic pattern reliably identifies the pathogen.
| Pattern | Common clues | Important caution |
|---|---|---|
| Viral | Rhinorrhea, diffuse findings, wheezing, gradual onset | Viral and bacterial infection can coexist |
| Typical bacterial | Higher fever, focal crackles, focal decreased air entry | No single symptom or examination finding confirms bacterial disease |
| Atypical | School age, persistent cough, headache, malaise | Presentation may overlap substantially with viral disease |
Differential Diagnosis
Not every fever, cough, and focal lung finding is pneumonia
Use the history, examination, age, risk factors, and illness trajectory to distinguish pneumonia from important mimics.
Viral bronchiolitis
Young infant with a viral prodrome, diffuse crackles or wheezing, and more generalized rather than persistent focal lung findings.
Asthma or viral-induced wheeze
Recurrent episodes, atopic history, prolonged expiration, diffuse wheezing, or previous improvement with bronchodilator therapy.
Foreign body aspiration
Abrupt onset after choking with unilateral wheezing or asymmetric air entry should prompt reconsideration of an infectious diagnosis.
Atelectasis
Can mimic focal pneumonia clinically and radiographically, particularly with mucus plugging or airway obstruction.
Aspiration
Consider swallowing dysfunction, neurologic impairment, impaired airway protection, recurrent episodes, or a clear aspiration event.
Pulmonary edema / heart failure
Cardiac disease, hepatomegaly, edema, feeding intolerance, poor growth, or diffuse bilateral pulmonary findings suggest a cardiogenic process.
Tuberculosis
A prolonged course, weight loss, persistent cough, known exposure, travel, or other epidemiologic risk should broaden the infectious differential.
Pulmonary embolism
Rare in children, but consider with pleuritic symptoms, unexplained hypoxemia, and important venous thromboembolism risk factors.
Malignancy or structural lesion
Persistent focal opacity or recurrent pneumonia in the same anatomic location should prompt evaluation for an obstructing or structural process.
Reconsider the diagnosis when the pattern does not fit
Diagnostic Workup
Testing should answer a clinical question
Uncomplicated pneumonia is often a clinical diagnosis. Escalate testing when severity, uncertainty, treatment failure, underlying disease, or suspected complications make the result actionable.
When less testing is usually more
A well-appearing child with uncomplicated suspected pneumonia who is oxygenating adequately and can be safely treated as an outpatient usually does not need extensive diagnostic testing.
- • Measure vital signs and oxygen saturation
- • Routine chest radiography is usually unnecessary
- • Routine CBC and inflammatory markers are usually unnecessary
- • Routine blood culture has low yield in uncomplicated disease
- • Viral testing is most useful when the result changes management
When additional testing becomes useful
Testing becomes more valuable when the result could change treatment, disposition, or the evaluation for complications.
- • Hypoxemia or significant respiratory distress
- • Toxic appearance or concern for sepsis
- • Hospitalization or significant underlying disease
- • Diagnostic uncertainty
- • Failure to improve as expected
- • Suspected pleural or parenchymal complication
Diagnostic stewardship
Choosing the right test
Different tests answer different questions. None should be used in isolation to determine the microbial cause of pneumonia.
| Test | When it may help | Limitation |
|---|---|---|
| Pulse oximetry | Assess severity and need for respiratory support | A normal value does not exclude pneumonia |
| Chest radiograph | Hypoxemia, significant distress, admission, failed treatment, or suspected complication | Cannot reliably determine viral versus bacterial etiology |
| Lung ultrasound | Evaluate suspected consolidation or pleural fluid | Operator dependent |
| CBC / CRP / procalcitonin | May support assessment of severe or complicated illness | Cannot independently distinguish bacterial from viral pneumonia |
| Blood culture | Severe disease, toxic appearance, complicated pneumonia, or selected hospitalized patients | Low yield in uncomplicated disease |
| Chest CT | Selected cases with unclear anatomy, necrosis, abscess, mass, or persistent disease | Radiation exposure; not routine |
Imaging pearl
Management
Treat the child, the likely pathogen, and the severity
Supportive care and antimicrobial decisions should reflect suspected etiology, illness severity, immunization status, comorbidities, local resistance patterns, and the ability to tolerate oral therapy.
Start with physiology
Stabilization comes before antimicrobial refinement. Address hypoxemia, respiratory distress, hydration, perfusion, and clinical deterioration while deciding whether bacterial infection is likely enough to warrant antibiotics.
Support the child
- • Provide oxygen when hypoxemic
- • Escalate respiratory support based on work of breathing
- • Maintain hydration with oral or IV fluids as appropriate
- • Use antipyretics for comfort
- • Use nasal suctioning in younger children when helpful
- • Reassess frequently for clinical deterioration
Decide whether antibiotics are needed
- • Avoid antibiotics when viral pneumonia is strongly favored
- • When bacterial CAP is suspected, use the narrowest effective agent
- • Consider age, immunization status, severity, and resistance risk
- • Adjust therapy when microbiologic data are clinically meaningful
- • Transition from IV to oral therapy when clinically appropriate
- • Reassess the diagnosis and complications when improvement does not occur as expected
Choose empiric therapy by clinical setting
The appropriate empiric regimen changes with the suspected etiology, severity of illness, treatment setting, and patient-specific risk factors.
| Clinical situation | Common approach | Key consideration |
|---|---|---|
| Suspected viral CAP | Supportive care without routine antibacterial therapy | Respiratory viruses cause most CAP in young children; antibiotics are not indicated when bacterial infection is not suspected |
| Uncomplicated outpatient bacterial CAP | Oral amoxicillin | Provides narrow-spectrum therapy targeting S. pneumoniae; confirm allergy history, local guidance, and reliable follow-up |
| Hospitalized uncomplicated bacterial CAP | IV ampicillin for most fully immunized children when local pneumococcal susceptibility supports its use | Avoid unnecessarily broad therapy; broaden when resistance risk, immunization status, severity, or other clinical factors warrant it |
| Suspected atypical pneumonia | Add or use a macrolide when an atypical pathogen is clinically suspected | Most relevant in school-aged children and adolescents; clinical findings alone do not reliably establish Mycoplasma infection |
| Concern for MRSA pneumonia | Add MRSA-active therapy according to local guidance | Consider especially with severe disease, compatible complications, or S. aureus superinfection following influenza |
| Complicated pneumonia | IV antimicrobial therapy plus evaluation for source control when indicated | Effusion size, respiratory compromise, purulence, microbiology, and local pathways help determine whether pleural drainage is required |
Treatment duration
Complications
Failure to improve should trigger a search for complicated pneumonia
Persistent fever, worsening respiratory status, significant unilateral findings, chest pain, or an unexpected clinical trajectory should prompt reassessment for pleural or parenchymal complications.
Complicated pneumonia should move the learner from simply asking “Which antibiotic?” to asking what has changed anatomically. Pleural fluid, organized infection, and parenchymal destruction can alter both imaging strategy and management.
Parapneumonic effusion
Inflammatory fluid accumulates in the pleural space adjacent to pneumonia.
Clinical clues
- • Persistent or worsening fever
- • Decreased breath sounds
- • Dullness to percussion
- • Increasing respiratory distress
Empyema
Pleural infection progresses to purulent or increasingly organized inflammatory material.
Clinical clues
- • Persistent systemic illness
- • Loculated or septated pleural fluid
- • Respiratory compromise
- • Failure to improve with antibiotics alone
Necrotizing pneumonia
Severe parenchymal inflammation causes tissue destruction, necrosis, and cavitation.
Clinical clues
- • Severe or prolonged illness
- • Persistent fever despite therapy
- • Cavitary parenchymal changes
- • Associated complicated pleural disease
Choose imaging based on the question
Imaging should escalate with the clinical question rather than simply with disease severity.
Chest radiograph
Useful for identifying air-space disease and suggesting a pleural effusion when complicated pneumonia is suspected.
Chest ultrasound
Best suited to characterizing pleural fluid, including its size, complexity, septations, and loculations, without ionizing radiation.
Chest CT
Reserve for selected cases when detailed evaluation of parenchymal destruction, cavitation, anatomy, or another complication will change management.
Imaging gallery
Imaging findings in complicated pneumonia
These examples demonstrate findings that may be seen with complicated pneumonia. Imaging findings are supportive rather than diagnostic in isolation because multiple pulmonary processes can produce similar appearances. Imaging should always be interpreted alongside the history, physical examination, laboratory findings, and clinical course.
Chest radiograph
Parapneumonic pleural effusion
Pleural fluid produces an upward-curving meniscus and blunting of the costophrenic angle adjacent to basilar airspace disease.
Radiopaedia Case: Pleural Effusion (Case 7)
Chest ultrasound
Complicated parapneumonic effusion / empyema
Internal echoes, septations, and loculations suggest an organized pleural infection and may influence drainage planning.
Radiopaedia Case: Thoracic Empyema (Case 8)
Chest CT
Necrotizing pneumonia
Multiple cavities embedded within consolidated lung suggest pulmonary necrosis and destruction of normal architecture.
Radiopaedia Case: Cavitating Pneumonia (Case 3)
Imaging is one piece of the clinical picture
Similar imaging findings may occur with infectious, inflammatory, congenital, and neoplastic processes. Imaging should be used to answer a focused clinical question and interpreted within the broader clinical context.
Evaluating pleural fluid
Chest ultrasound is particularly useful for confirming pleural fluid, estimating its size, and identifying septations or loculations. Management ranges from antibiotics and observation to drainage with a chest tube, fibrinolytic therapy, or surgery, depending on respiratory compromise and the character and size of the collection.
Disposition
Match the care setting to physiologic severity
Oxygen requirement, work of breathing, hydration, perfusion, mental status, complications, underlying disease, and reliable follow-up determine where treatment can occur safely.
Think in terms of required support
Disposition is not determined by the diagnosis of pneumonia itself. Choose the care setting based on the respiratory, hydration, monitoring, and treatment support the child requires.
Consider discharge
- • Well appearing
- • No significant hypoxemia
- • Minimal work of breathing
- • Tolerating oral fluids and medication
- • Reliable caregivers and follow-up
- • No concerning complication
Consider admission
- • Persistent oxygen requirement
- • Moderate or worsening respiratory distress
- • Inability to maintain hydration
- • Toxic appearance or concern for sepsis
- • Failed outpatient therapy
- • Complicated pneumonia
- • High-risk underlying condition
- • Unsafe or unreliable follow-up
Consider ICU care
- • Escalating oxygen requirement
- • Need for noninvasive or invasive ventilation
- • Apnea or exhaustion
- • Altered mental status
- • Hemodynamic instability
- • Severe sepsis or organ dysfunction
Trajectory matters
Return precautions
- • Increasing work of breathing
- • Cyanosis, apnea, or abnormal sleepiness
- • Inability to drink or markedly decreased urine output
- • Persistent vomiting
- • Worsening fever or clinical condition
- • Failure to begin improving within the expected timeframe
Clinical Pearls
High-yield lessons to carry forward
Severity beats a single exam finding
The chest X-ray cannot name the pathogen
Not every pneumonia needs antibiotics
Remember the abdomen
Wheezing does not exclude pneumonia
Failure to improve is a diagnostic clue
Location matters in recurrent pneumonia
Reassess before broadening antibiotics
Knowledge Check
Can you manage the child—not just recognize pneumonia?
Apply severity assessment, diagnostic stewardship, and antimicrobial reasoning to a child with suspected community-acquired pneumonia.
Question 1
A previously healthy 4-year-old has fever, cough, focal crackles, mild increased work of breathing, oxygen saturation 95% on room air, and is drinking adequately. Bacterial community-acquired pneumonia is suspected. What is the most appropriate initial antibiotic?
Anki Deck
Pneumonia Anki Deck
Reinforce the highest-yield concepts from this module with 16 spaced-repetition cards.
Requires Anki. Deck content is intended for educational review and should be used alongside the full PediAtlas module.
Evidence Base
Clinical References
Current PIDS/IDSA guideline update addressing pediatric pneumonia complicated by parapneumonic effusion or empyema, including imaging and drainage decisions.
Current AAP antimicrobial guidance for pediatric community-acquired pneumonia, including empiric therapy, atypical and MRSA coverage, oral transition, and treatment duration.
Foundational 2011 PIDS/IDSA pediatric CAP guideline. Retained for topics not yet replaced by the focused 2026 guideline update.
Institutional evidence-based guideline for the evaluation and management of pediatric community-acquired pneumonia.
AAP Pediatric Care Online clinical overview of pneumonia in children.
Global epidemiology, prevention, risk factors, and public-health overview of childhood pneumonia.
Educational Disclaimer
PediAtlas is intended for medical education and should not replace institutional guidelines, local protocols, patient-specific assessment, or clinical judgment.