Community Acquired Pneumonia

1. Definition and Classification

Pneumonia: Infection of the lung parenchyma.

Classification

Community Acquired Pneumonia (CAP): Infection acquired within the community.
Hospital Acquired Pneumonia (HAP):
- Pneumonia occurring > 48 hours after admission.
- Was not present at the time of admission.
- Note: The 48-hour window roughly corresponds to the incubation period of most hospital flora.
Ventilator Associated Pneumonia (VAP):
- Subtype of HAP.
- Occurs > 48 hours after invasive mechanical ventilation.

Changes in Terminology

The term "Healthcare Associated Pneumonia" (HCAP) is no longer used. Patients previously classified under HCAP are now reclassified as CAP.

2. Pathophysiology: Aspiration Pneumonia

Mechanism: Macro-aspiration of oropharyngeal contents.
Prevalence: Accounts for roughly 10–15% of all CAP cases.
Microbiology: Predominantly Gram-negative bacilli and Anaerobes.
Risk Factors: Poor dentition, neuromuscular disease, stroke, dementia.

3. Etiology (Microbiology)

Pediatric

Unlike adults, clinical signs in children strongly suggest the organism type.

Feature	Viral	Streptococcal	Staphylococcal	Atypical (Mycoplasma)
Onset	Gradual; follows URTI.	Rapid progression.	Rapid; "Toxic" look.	Gradual; "Walking pneumonia".
Toxicity	Less toxic.	More toxic.	Very toxic.	Not very sick.
Chest Exam	Wheezing common; Bilateral.	Lobar involvement.	Diffuse; Pneumatoceles.	Diffuse/Patchy.
Complications	Self-limiting (3-5 days).	Empyema possible.	Empyema, Abscess, Pneumothorax.	Wheezing.
Key Associations	Bronchiolitis-like features.		Necrotizing pneumonia; Pyodermas.	Older children (>5y).

Adult

A. Broad Categories

Category	Characteristics	Organisms
Typical	Conventional bacteria; grow on standard media.	Streptococcus pneumoniae (Most Common) Haemophilus influenzae Moraxella catarrhalis CA-MRSA (Methicillin-Resistant S. aureus) Klebsiella pneumoniae
Atypical	Do not grow on conventional culture media.	Mycoplasma pneumoniae Legionella pneumophila (Serovar 1) Chlamydia pneumoniae
Viral	Can cause epidemics/pandemics/endemics.	Influenza, Parainfluenza SARS-CoV-2 (COVID-19) Human Metapneumovirus RSV (Respiratory Syncytial Virus) Rarely: Adenovirus, Rhinovirus (usually URTI)
Chronic/Rare	Longer symptom duration; often immunocompromised.	Mycobacterium tuberculosis (TB) NTM (Non-Tuberculous Mycobacteria) Endemic Fungi Nocardia, Actinomycetes

B. Organisms by Severity

Mild Infection (Outpatient): S. pneumoniae, Mycoplasma, Chlamydia, Viruses.
Severe Infection (Hospitalized/ICU):
- Legionella: The only atypical organism typically associated with severe disease and HAP.
- CA-MRSA: Necrotizing pneumonia, abscess formation.
- Gram-negative bacilli: Multi-lobar involvement.

C. Clinical Risk Factors & Associated Pathogens

Risk Factor	Associated Organisms	Pathophysiology/Notes
Alcoholism	Oral Anaerobes, Klebsiella, Acinetobacter, Mycobacterium tuberculosis	Aspiration risk; compromised immunity.
COPD / Smokers	Moraxella catarrhalis, Pseudomonas aeruginosa	Structural lung changes.
Structural Lung Disease (e.g., Bronchiectasis)	Pseudomonas aeruginosa, Burkholderia cepacia	Biofilms; leads to recurrent exacerbations and poor prognosis.
Aspiration Risk (Stroke, Dementia)	Oral Anaerobes, Enteric GNB (E. coli, Klebsiella)	Macro-aspiration.
Lung Abscess	Anaerobes, CA-MRSA, TB, Fungi, Nocardia	Often polymicrobial.
Travel to Ohio/St. Lawrence River/Ganga River Valley	Histoplasma capsulatum
Bird Exposure	Chlamydia psittaci (Parrots), Histoplasma (Excreta)
Rabbit Exposure	Francisella tularensis
Sheep/Goat/Unpasteurized Milk	Coxiella burnetii (Q Fever)
Post-Influenza	CA-MRSA, S. pneumoniae	Important: Influenza predisposes to secondary bacterial superinfection.

4. Clinical Features & Extra-Pulmonary Manifestations

Typical Symptoms

Fever
Cough
Shortness of breath
Chest pain (pleuritic)
Hemoptysis (rare, consider necrotizing pneumonia/abscess)

Specific Organism Manifestations

High Yield Associations

Legionella: Hyponatremia, Cerebral Ataxia, Glomerulonephritis. (Can cause epidemics via water vents).
Mycoplasma: Encephalitis, Cranial Nerve Palsies.
CA-MRSA: Necrotizing pneumonia, lung abscess, Pneumatoceles (thin-walled cavities).
Pneumatoceles Causes: Staphylococcus, Klebsiella, Toxic Kerosene poisoning.

Indications for Admission (Triaging)

Admit if ANY of the following are present:

Age < 3 months (Always admit).
Oxygen Saturation ( $S p O_{2}$ ) < 92%.
Marked Tachypnea: >20 breaths/min above the age-specific cutoff.
Apnea or Grunting.
Failure of OPD treatment (No improvement after 48 hours).
Severe malnutrition or refusal to feed.

5. Diagnosis

A. General Approach

Diagnosis is Clinical + Radiological.
Microbiological Testing: NOT required for mild/outpatient CAP.
Indications for Testing:
1. Severe CAP (Hospitalized).
2. Risk factors for MDR (Multi-Drug Resistant) organisms.

B. Radiological Patterns

Lobar Pneumonia: Typical bacteria (Strep. pneumo).
Bronchopneumonia: Diffuse/patchy; Aspiration, Typical bacteria, TB.
Interstitial: Viral, Atypical organisms.

C. Microbiological Tests (Severe CAP only)

Test	Indication/Notes
Sputum Gram Stain	Quality Control: Valid only if <10 Epithelial cells and >25 Pus cells per HPF. Assesses if sample is LRT vs Saliva.
Sputum Culture	Sensitivity ~50% in severe CAP.
Blood Culture	Sensitivity poor (10–15%). Perform in all hospitalized patients.
Urine Antigen	Tests for Pneumococcus and Legionella (Serovar 1).
Viral PCR	Influenza/COVID-19 throat swabs if seasonal/epidemic.

BioFire / Multiplex PCR Panels

While widely used in private settings to test for viruses/bacteria simultaneously, current guidelines do not recommend routine upfront use for all CAP patients. Reserve for cases with negative cultures and failure to respond.

D. Inflammatory Markers (CRP / Procalcitonin)

Role: NOT used to diagnose pneumonia or decide if antibiotics are needed.
Utility: Used to monitor response and de-escalate/stop treatment.
Monitoring: Repeat at 72–96 hours.

6. Severity Assessment

Determines the site of care (Outpatient vs Ward vs ICU).

Pediatric

A. Respiratory Rate Thresholds (Fast Breathing)

Age Group	Respiratory Rate Criteria for Pneumonia
2 months – 12 months	$\geq 50$ / min
> 1 year – 5 years	$\geq 40$ / min
> 5 years	$\geq 30$ / min

B. Revised WHO Classification (2014)

Classification	Clinical Findings	Action
No Pneumonia	Cough and cold; no fast breathing.	Home care.
Pneumonia	Fast breathing AND/OR Chest indrawing.	Oral Antibiotics (OPD).
Severe Pneumonia	General Danger Signs or Hypoxia ( $S p O_{2} < 92 %$ ).	Hospitalize + IV Antibiotics + $O_{2}$ .

General Danger Signs (Indications for Severe Pneumonia)

Inability to drink/feed.
Persistent vomiting.
Convulsions.
Lethargy or Unconsciousness.
Stridor in a calm child.
Severe Malnutrition.

Adult

A. IDSA/ATS Severe CAP Criteria

Definition of Severe CAP: Presence of 1 Major OR ≥ 3 Minor criteria.

Major Criteria:
1. Septic Shock requiring vasopressors.
2. Need for Invasive Mechanical Ventilation.
Minor Criteria:
- Respiratory Rate ≥ 30
- PaO2/FiO2 ratio ≤ 250
- Multi-lobar infiltrates
- Confusion/Disorientation
- Uremia (BUN ≥ 20 mg/dL)
- Leukopenia (WBC < 4000)
- Thrombocytopenia (Plt < 100,000)
- Hypothermia
- Hypotension requiring fluid resuscitation

B. CURB-65 Score (only in adults)

Simple, frequently used, but lacks sensitivity/specificity compared to others.

Parameter	Criteria
C	Confusion
U	Urea (BUN) > 20 mg/dL (or > 7 mmol/L)
R	Respiratory Rate ≥ 30
B	Blood Pressure (Systolic < 90 OR Diastolic ≤ 60)
65	Age ≥ 65

Scoring & Management:

0: Outpatient (Home).
1: Outpatient (unless score is 1 due to non-age factor, then consider admit).
2: Hospitalize (Ward).
3–5: Hospitalize (Ward or ICU; 4-5 usually ICU).

C. Other Scores

Pneumonia Severity Index (PSI): Complex (20 parameters). Class I-II (Outpatient), Class III (Outpatient/Obs), Class IV-V (Inpatient/ICU).
SMART-COP: Best predictor of mortality and need for ICU/vasopressors.

7. Management (Antibiotic Therapy)

Key Considerations for Drug Choice

Severity (Mild vs Severe).
Comorbidities (CKD, DM, CLD, Malignancy, Structural Lung Disease).
MDR Risk Factors:
- Prior isolation of MDR organism.
- Hospitalization in last 3 months.
- IV/Oral antibiotic use in last 3 months.

Antibiotic Resistance Context

Beta-Lactam Resistance: Rare in S. pneumoniae (<1%).
Macrolide Resistance: Common in S. pneumoniae (20–50%).
- Implication: Do not use Macrolide monotherapy for S. pneumoniae if resistance is suspected; use combination or fluoroquinolone.

Treatment Regimen (Pediatrics)

A. Outpatient (Oral) Treatment

Duration: 5 days typically.
No Investigations needed for OPD cases

Age Group	First Line Therapy	Notes
< 3 Months	ADMIT	Do not treat as outpatient.
3 mo – 5 Years	Amoxicillin (80 mg/kg/d BD)	In India, 40–50 mg/kg/d is sufficient as penicillin resistance is <10%.
> 5 Years	Amoxicillin OR Macrolide (Azithromycin)	Azithromycin covers Mycoplasma (common in >5y). Dose: 10 mg/kg OD (empty stomach).

Linezolid Caution

Linezolid is listed as an option for suspected MRSA, but strictly classified as a reserve drug for Tuberculosis (TB) by the National TB Elimination Programme (NTEP). Use with caution.

B. Inpatient (IV) Treatment

Age Group	First Line	Second Line / Severe	Suspected Staph. aureus
< 3 Months	Cefotaxime or Pip-Tazo (+ Gentamicin/Amikacin)	Meropenem (if severe/resistant)	Add Vancomycin or Linezolid.
3 mo – 5 Years	Ampicillin (100–200 mg/kg/d)	Ceftriaxone or Co-amoxiclav	Add Cloxacillin (50–100 mg/kg/d) or Vancomycin.
> 5 Years	Ampicillin or Co-amoxiclav	Ceftriaxone (+ Azithromycin if atypical suspected)	Same as above.

C. Duration of Therapy

Standard Bacterial CAP: 7–10 days.
Methicillin-Susceptible S. aureus (MSSA): 7–10 days.
MRSA / Staph with Complications:
- No complications: 14 days.
- Complications (Empyema/Abscess): 4–6 weeks.

D. Viral Pneumonia (H1N1) Management

Oseltamivir Indication: If H1N1 suspected, initiate within 3 days.
Dosing (Treatment):
- < 1 year: 3 mg/kg BD.
- > 1 year (≤15 kg): 30 mg BD.
- > 1 year (>15-23 kg): 45 mg BD.
- > 1 year (>23-40 kg): 60 mg BD.

Treatment Regimens (Adult)

1. Outpatient Management

Patient Profile	Preferred Treatment	Alternative
Healthy (No comorbidities, No MDR risk)	Beta-Lactam (e.g., Amoxicillin) + Macrolide (Azithromycin) OR Doxycycline	Monotherapy with Doxycycline or Macrolide (less preferred due to resistance).
Comorbidities (Heart/Lung/Liver/Renal/DM/Alcohol) OR MDR Risk	Beta-Lactam + Beta-Lactamase Inhibitor (Amox-Clav) + Macrolide	Monotherapy with Respiratory Fluoroquinolone (Levofloxacin, Moxifloxacin, Gemifloxacin). Not Ciprofloxacin.

Dosing Note: Azithromycin dose is 500mg Day 1, then 250mg for 4 days. Levofloxacin dose is 750mg/day.

2. Inpatient Management (Hospitalized)

Severity / Risk	Treatment Strategy
Non-Severe (No MDR Risk)	Beta-Lactam + Macrolide OR Respiratory Fluoroquinolone.
Severe CAP (No MDR Risk)	Beta-Lactam + Macrolide. (Do not wait for cultures).

3. Management of MDR Risk Factors

MDR Risks: Prior isolation, Hospitalization, or Antibiotic use in prior 3 months.

Scenario	Strategy
Non-Severe + MDR Risk	Start Standard Therapy (Beta-Lactam + Macrolide). Obtain Cultures. If culture (+): Add MDR coverage. If culture (-): Continue standard.
Severe + MDR Risk	Start Broad Spectrum Immediately. Cover MRSA + Pseudomonas. Obtain Cultures. De-escalate if cultures are negative.
Prior Isolation History	Treat immediately regardless of severity.

MDR Coverage Drugs:

MRSA: Vancomycin or Linezolid (or Teicoplanin).
Pseudomonas: Pip-Tazo, Cefepime, Ceftazidime, Meropenem/Imipenem.

Duration of Treatment

Minimum: 5 days.
Extension: Extend if inadequate clinical response.
De-escalation: Can stop if Procalcitonin falls by >80% or value is < 0.5.

8. Adjunctive Therapy:

Corticosteroids (adults)

Evidence: The CAPE COD Trial.

Indication: Severe CAP Only (Mechanical ventilation, Shock, PSI Class V, or High Flow O2 requirement).
Drug/Dose: Hydrocortisone 200mg/day (continuous infusion).
Benefit: Significant reduction in mortality (11-12% down to 6-7%).
Duration: 8 to 14 days (taper early if rapid improvement).
Contraindication: Influenza Pneumonia. (Steroids cause harm in influenza).
- Clinical Dilemma: If patient has COPD/Asthma exacerbation + Influenza, use steroids for the exacerbation if necessary, but avoid for pure influenza pneumonia.

Zinc and Vitamin D3 (children)

Nutrient	Theoretical Benefit	Evidence as Treatment (Adjuvant)	Evidence as Prevention
Zinc	Immune boost; tissue repair	Mixed. Benefits likely limited to deficient/malnourished children.	Strong. Reduces incidence of pneumonia.
Vitamin D3	Antimicrobial peptides; immune regulation	Weak. Most trials show no reduction in hospital stay or recovery time.	Strong. Correction of deficiency reduces risk of infection.

9. Monitoring and Resolution

Timeline of Improvement

Fever: Resolves in 48 hours.
Hypoxia/Tachycardia/Distress: Improves in 72–96 hours.
Cough: Persists for 2–3 weeks.
Chest X-Ray: Resolution takes 1–3 months.

Treatment Failure (Non-Resolving Pneumonia)

If no improvement after 72 hours, consider:

Wrong Diagnosis: PE, ILD, Vasculitis, Cancer, Organizing Pneumonia.
Wrong Bug: TB, Fungi, Nocardia, MDR organism.
Wrong Drug/Dose: Resistance, under-dosing.
Complications: Empyema, Lung Abscess (require drainage/prolonged antibiotics).

Follow-up X-Ray

Severe CAP: Always repeat X-ray.
Mild CAP: Repeat only if risk factors for malignancy exist (Age > 50, Smoker).
- Reason: To rule out post-obstructive pneumonia secondary to malignancy.