Community Acquired Pneumonia

OVERVIEW

• single organism (often)
• Streptococcus pneumonia (most common organism)
• other causes: Mycoplasma pneumoniae, Chlamydophila pneumoniae and Legionella, Haemophilus influenzae (in COPD)

CLINICAL FEATURES

• cough, fever, shortness of breath, pleuritic chest pain, fatigue, sputum (rust coloured classically suggests pneumococcus)
• tachypnea, hypoxia, respiratory distress, increased work of breathing, bronchial breath sounds, crackles

Risk factors for Severe Infection

• elderly
• co-morbidity
• smoking
• alcohol abuse
• failure to contain infection @ entry site
• immunosuppression
• genetic polymorphism

ASSOCIATIONS

• alcoholism — Streptococcus pneumoniae, anaerobes, Gram negatives such as Klebsiella pneumonia, tuberculosis
• COPD/ smoker — Streptococcus pneumoniae, Haemophilus influenzae, Moraxella catarrhalis
• nursing home resident — Streptococcus pneumoniae, Gram negatives, Haemophilus influenzae, S. aureus, Chlamydophila pneumoniae consider tuberculosis and anaerobes (but less common)
• poor dental hygiene — anaerobes
• bat/ cave exposure — Histoplasma capsulatum
• bird exposure — Chlamydophila psitacci, Cryptococcus neoforms, Histoplasma capsulatum
• rabbit exposure — Franciscella tularensis
• exposure to farm animals or parturient cats — Coxiella burnetti (Q fever)
• post-infuenza — S. pneumoniae, S. aureus
• brochiectasis, cystic fibrosis — Pseudomonas aeroginosa, S. pneumoniae, Burkholderia cepacia
• sickle cell disease, asplenia — S. pneumoniae, H. influenzae
• Suspected bioterrorism — Anthrax
• Tropical Australia — melioidosis, Acinetobacter
• Potting mix — Legionella longbeachae
• Travel to Asia — SARS, tuberculosis, meliodosis

INVESTIGATIONS

• CXR
• CT: helps identify loculated effusion, helpful in non-responders
• blood culture: only 15% positive
• sputum gram stain: can help with defining predominate organisms
• sputum culture: use if drug-resistant or unusual organism suspected
• ABG: hypercapnia, hypoxemia
• serology: legionella, Chlamydia, mycobacterium, viruses (requires acute and convalescent titers -> not usually recommended)
• legionella urinary antigen: sensitivity 60%, specific to serogroup 1 (quadravalent assay now available)
• pneumococcal antigen: sensitivity 70-100%, specificity 80%, false positives if has had recent pneumococcal infection

RISK STRATIFICATION

• multiple scores have been looked to predict severity and outcome: Pneumonia severity score, CURB-65 score, SMART COP, CAP PIRO

SMART COP

• Australian Community Acquired Pneumonia Study -> looked at variable predicting the requirement for intensive respiratory or vasoactive support
• initially 882 prospective episodes looked at -> points based severity tool designed -> validated in 7464 patients
• more sensitive than CURB-65 or IRVS
• score of >/= 4 correlated with a 1/3 chance of requiring intensive respiratory or vasoactive support

S – systolic BP < 90mmHg
M – multilobe infiltrate
A – albumin < 35g/L
R – RR (age adjusted < 50yrs >25/min, > 50yrs >30/min)
T – tachycardia > 125/min
C – confusion (acute onset)
O – oxygenation (age adjusted: SpO2 < 93%, PaO2 < 70mmHg, PF < 333mmHg)
P – pH < 7.35

MANAGEMENT

• antibiotics within 4 hours

Non-tropical

• Pneumococcus + atypical cover
• mild: amoxicillin + clarithromycin PO
• moderate: penicillin IV + clarithromycin PO (+gentamicin if risk factors)
• severe: ceftriaxone + clarithromycin IV

Tropical

• need to cover Burkholderia pseudomallei and Acinetobacter baumannii
• meropenem/imipenem + azithromycin/erthyromycin