# Community-Acquired Pneumonia: Pediatric and Adult Guidelines Compared

## Overview
Community-acquired pneumonia (CAP) is a leading cause of hospitalization and mortality across all ages. Etiology differs sharply by age group: viral pathogens dominate in young children, while bacterial causes are more prominent in adults. Pediatric (AAP/PIDS) and adult (IDSA/ATS) guidelines diverge on imaging requirements, empiric antibiotic selection, and disposition decisions. The Med-Peds physician must be facile with both frameworks.

## Epidemiology
Leading infectious cause of death in children <5 worldwide. US pediatric hospitalization rate: approximately 15-20 per 10,000 children/year. US adult CAP incidence: 2-5 per 1,000 adults/year; increases dramatically with age. Mortality: <1% outpatient adults, 5-15% hospitalized adults, 20-50% ICU-admitted adults. Pneumococcal conjugate vaccines (PCV13, PCV15, PCV20) have dramatically reduced invasive pneumococcal disease in both children and adults.

## Etiology by Age

### Neonates (<1 month)
Group B Streptococcus (GBS); Gram-negative enterics (E. coli, Klebsiella); Listeria monocytogenes; HSV, CMV (congenital); Chlamydia trachomatis (afebrile pneumonitis, 2-12 weeks).

### Infants and Preschool (1 month - 5 years)
**Viral (most common)**: RSV, rhinovirus, influenza, parainfluenza, human metapneumovirus, adenovirus. **Bacterial**: Streptococcus pneumoniae (most common bacterial cause), Staphylococcus aureus (including MRSA -- consider with necrotizing pneumonia or empyema), Haemophilus influenzae (non-typeable), Moraxella catarrhalis. **Atypical**: uncommon in this age group.

### School-Age Children (5-18 years)
**Mycoplasma pneumoniae**: most common cause in ages 5-18; "walking pneumonia". **Streptococcus pneumoniae**: remains important. **Chlamydophila pneumoniae**: adolescents. **Viral**: less dominant but still common, especially influenza. **S. aureus**: consider with severe, necrotizing, or post-influenza pneumonia.

### Adults
**Streptococcus pneumoniae**: most commonly identified bacterial pathogen. **Mycoplasma pneumoniae**: young adults. **Haemophilus influenzae**: COPD, smokers. **Respiratory viruses**: influenza, SARS-CoV-2, RSV (especially elderly) **Legionella pneumophila**: hotel/travel exposure, contaminated water; can cause severe disease. **Chlamydophila pneumoniae**. **Staphylococcus aureus**: post-influenza, IV drug use. **Gram-negative bacilli**: elderly, nursing home residents, alcoholism. **Anaerobes**: aspiration pneumonia (poor dentition, dysphagia, altered consciousness) In up to 50-60% of adult CAP, no pathogen is identified despite testing.

## Diagnosis

### Pediatric Approach (AAP/PIDS 2011 Guidelines)
**Clinical diagnosis is sufficient** in outpatient children with typical findings. Chest radiograph is NOT routinely recommended for outpatient management of children with suspected uncomplicated CAP. CXR indications: hospitalization required, treatment failure, severe disease, concern for complications (effusion, empyema) **Blood cultures**: NOT routinely recommended for outpatient; obtain in hospitalized children with moderate-severe disease. **Viral testing**: nasopharyngeal PCR panel useful to guide therapy (positive viral test may reduce unnecessary antibiotics) **Sputum**: not obtainable in young children; adolescents may produce sputum. **WBC, CRP, procalcitonin**: not reliable for distinguishing viral from bacterial; procalcitonin has modest utility.

### Adult Approach (IDSA/ATS 2019 Guidelines)
**Chest radiograph**: recommended for ALL patients with suspected pneumonia; required for definitive diagnosis. **Sputum Gram stain and culture**: recommended for inpatients (especially ICU), NOT routinely for outpatients. **Blood cultures**: recommended for severe CAP and ICU patients; not routinely for non-severe inpatients. **Legionella and pneumococcal urinary antigen testing**: for severe CAP or ICU admission. **Respiratory viral panel**: during influenza season; consider broader panel in immunocompromised. **Procalcitonin**: may help guide antibiotic duration; low levels (<0.25 ng/mL) may support withholding or stopping antibiotics.

## Severity Assessment

### Pediatric Indicators of Severe Disease
Respiratory distress: tachypnea (age-specific thresholds), retractions, grunting, nasal flaring. Hypoxia: SpO2 <90% (criteria for hospitalization) Dehydration or inability to maintain oral intake. Toxic appearance, altered mental status. Complicated pneumonia: parapneumonic effusion, empyema, necrotizing pneumonia, lung abscess.

### Adult Severity Scores
**CURB-65**: Confusion, Uremia (BUN >20), Respiratory rate >=30, Blood pressure (SBP <90 or DBP <=60), Age >=65. 0-1: outpatient; 2: consider short hospitalization; 3-5: hospitalize (4-5 consider ICU) **PSI/PORT Score**: 20 variables; more complex but well-validated; Class I-III outpatient, IV-V inpatient. **IDSA/ATS Severe CAP Criteria (for ICU admission)**: 1 major (mechanical ventilation or septic shock requiring vasopressors) OR >=3 minor (RR >=30, PaO2/FiO2 <=250, multilobar infiltrates, confusion, BUN >=20, WBC <4000, platelets <100K, hypothermia, hypotension requiring fluids)

## Empiric Antibiotic Therapy

| Setting | Pediatric | Adult |
|---------|-----------|-------|
| Outpatient (typical) | Amoxicillin 90 mg/kg/day BID-TID | Amoxicillin 1 g TID or doxycycline 100 mg BID |
| Outpatient (atypical) | Azithromycin 10 mg/kg day 1, 5 mg/kg days 2-5 | Azithromycin (if resistance <25%) or doxycycline |
| Outpatient (comorbidities) | Amoxicillin + azithromycin | Respiratory FQ or beta-lactam + macrolide |
| Inpatient (non-severe) | Ampicillin IV 150-200 mg/kg/day q6h | Beta-lactam + macrolide or respiratory FQ monotherapy |
| Inpatient (severe/ICU) | Ceftriaxone + azithromycin ± vancomycin | Beta-lactam + macrolide (preferred) ± MRSA/Pseudomonas coverage |

### Outpatient Pediatric CAP
**Preschool (presumed viral)**: supportive care; antibiotics NOT routinely needed if viral etiology strongly suspected. **If bacterial CAP suspected (preschool)**: amoxicillin 90 mg/kg/day divided BID-TID (high-dose to cover intermediate-resistance pneumococcus) **School-age/adolescent**: amoxicillin (if typical pneumonia) OR azithromycin 10 mg/kg day 1, then 5 mg/kg days 2-5 (if atypical pneumonia suspected) **Combination**: amoxicillin + azithromycin if both typical and atypical coverage needed. **Penicillin allergy**: azithromycin, clindamycin, or respiratory fluoroquinolone (avoid FQs in children if possible)

### Inpatient Pediatric CAP
**Non-severe, fully immunized**: ampicillin IV 150-200 mg/kg/day divided q6h (or penicillin G) -- narrow spectrum, excellent pneumococcal coverage. **Atypical coverage needed**: add azithromycin. **Severe/ICU**: ceftriaxone 50-100 mg/kg/day + azithromycin; add vancomycin or clindamycin if MRSA suspected. **Influenza-associated**: add oseltamivir; consider MRSA coverage (vancomycin or linezolid)

### Outpatient Adult CAP
**No comorbidities**: amoxicillin 1 g TID OR doxycycline 100 mg BID OR azithromycin 500 mg day 1, then 250 mg days 2-5 (only if local macrolide resistance <25%) **With comorbidities** (chronic lung/heart/liver/renal disease, DM, alcoholism, immunosuppression, antibiotic use within 90 days): respiratory fluoroquinolone (levofloxacin 750 mg daily or moxifloxacin 400 mg daily) OR amoxicillin-clavulanate 2 g BID or cephalosporin (cefpodoxime, cefuroxime) + macrolide or doxycycline.

### Inpatient Adult CAP (Non-ICU)
Beta-lactam (ampicillin-sulbactam 3 g q6h, ceftriaxone 1-2 g daily, or cefotaxime) + macrolide (azithromycin) OR respiratory fluoroquinolone monotherapy.

### Inpatient Adult CAP (ICU)
Beta-lactam (ceftriaxone, ampicillin-sulbactam, or cefotaxime) + macrolide (preferred over FQ) OR beta-lactam + respiratory FQ. Add vancomycin or linezolid if MRSA suspected. Add piperacillin-tazobactam, cefepime, or meropenem if Pseudomonas risk factors.

## Treatment Duration
**Pediatric**: 7-10 days for typical bacterial CAP; 5 days may be sufficient for uncomplicated cases with rapid clinical improvement; azithromycin 5-day course for atypical. **Adult**: minimum 5 days; continue until afebrile >=48 hours and clinically stable; longer courses for empyema, lung abscess, MRSA, Pseudomonas.

## Complications

### Parapneumonic Effusion and Empyema
More common in children than adults. Pediatric: ultrasound-guided thoracentesis for moderate-large effusions; fibrinolysis (tPA/DNase via chest tube) or VATS for empyema. Adult: thoracentesis indicated for effusions >10 mm; empyema (pus, pH <7.2, glucose <60, positive Gram stain) requires chest tube drainage; fibrinolysis or VATS if loculated. Most common organisms: S. pneumoniae, S. aureus, GAS, anaerobes.

### Necrotizing Pneumonia
Consider S. aureus (MRSA), PVL-positive strains. More common in children and young adults. May require prolonged antibiotics; surgical intervention rarely needed.

### Lung Abscess
Mixed anaerobic and aerobic organisms. Prolonged antibiotic course (4-8 weeks) CT-guided drainage if >6 cm or not responding to antibiotics.

## Prevention
**Pneumococcal vaccines**: PCV13/PCV15 for all children (2, 4, 6, 12-15 months); PCV20 for adults >=65 or >=19 with risk factors. **Influenza vaccine**: annual for all >=6 months. **COVID-19 vaccine**: per current recommendations. **RSV prophylaxis**: nirsevimab for infants <8 months entering first RSV season; RSV vaccine for adults >=60 and pregnant individuals (32-36 weeks)

<image>A pathogen frequency chart organized by age group from neonates to elderly adults. Each age group column shows the most common organisms in descending order of frequency, with bacterial pathogens in red, viral pathogens in blue, and atypical pathogens in green. Visual emphasis shows the shift from viral-dominant etiology in young children to bacterial-dominant in adults, with Mycoplasma peaking in the school-age/adolescent age group. Key organisms are illustrated with representative microscopy or culture images.</image>

<image>A side-by-side comparison of empiric antibiotic selection for CAP in pediatric versus adult patients. The left panel shows the pediatric approach: outpatient (amoxicillin high-dose for typical, azithromycin for atypical) and inpatient (ampicillin IV for non-severe, ceftriaxone plus azithromycin for severe). The right panel shows the adult approach: outpatient without comorbidities (amoxicillin or doxycycline), outpatient with comorbidities (respiratory FQ or beta-lactam plus macrolide), non-ICU inpatient (beta-lactam plus macrolide or FQ monotherapy), and ICU (beta-lactam plus macrolide). Connecting lines highlight where the same antibiotics are used across ages and where they diverge.</image>

<image>A clinical decision algorithm for managing parapneumonic effusion and empyema across ages. Starting with identification of pleural effusion on imaging, the flowchart shows decision points: size assessment (ultrasound), thoracentesis with fluid analysis (pH, glucose, LDH, Gram stain, culture), and management branches for simple parapneumonic effusion (antibiotics alone), complicated parapneumonic effusion (chest tube with or without fibrinolytics), and empyema (VATS or fibrinolysis through chest tube). Pediatric and adult differences in approach are annotated at each branch.</image>

## Clinical Pearls
Chest radiograph is NOT routinely needed for outpatient pediatric CAP -- clinical diagnosis is sufficient per AAP/PIDS guidelines. High-dose amoxicillin (90 mg/kg/day) is the first-line antibiotic for outpatient pediatric bacterial CAP -- it provides excellent pneumococcal coverage including intermediate-resistance strains. For hospitalized pediatric CAP in fully immunized children, ampicillin IV is preferred over broader-spectrum agents -- narrow-spectrum therapy is appropriate. In adults, use CURB-65 or PSI to guide disposition -- these scores prevent unnecessary admissions and identify patients needing ICU care. Fluoroquinolones should be avoided in children when alternatives exist -- reserve for situations where no other option is appropriate. A positive viral panel in a child with mild pneumonia may safely allow withholding of antibiotics. Parapneumonic effusions are more common in children; ultrasound should be used early to evaluate for effusion in any child not improving on appropriate antibiotics. Dexamethasone as adjunctive therapy in adult CAP has emerging evidence for reducing mortality in severe disease (CAPE-COD trial) but is not yet standard.

## References
- Bradley JS, Byington CL, Shah SS, et al. The management of community-acquired pneumonia in infants and children older than 3 months of age: clinical practice guidelines by PIDS and IDSA. Clin Infect Dis. 2011;53(7):e25-e76.
- Metlay JP, Waterer GW, Long AC, et al. Diagnosis and treatment of adults with community-acquired pneumonia: an official clinical practice guideline of the ATS and IDSA. Am J Respir Crit Care Med. 2019;200(7):e45-e67.
- Jain S, Williams DJ, Arnold SR, et al. Community-acquired pneumonia requiring hospitalization among US children (CDC EPIC study). N Engl J Med. 2015;372(9):835-845.
- Jain S, Self WH, Wunderink RG, et al. Community-acquired pneumonia requiring hospitalization among US adults (CDC EPIC study). N Engl J Med. 2015;373(5):415-427.
- Dagan R, Bhutta ZA, de Quadros CA, et al. The remaining challenge of pneumonia: the leading killer of children. Pediatr Infect Dis J. 2011;30(1):1-2.