3.2 Community-Acquired Pneumonia, Hospital-Acquired Pneumonia & Tuberculosis
Key Takeaways
CURB-65 assigns one point each for new Confusion, Urea >7 mmol/L, Respiratory rate >=30/min, systolic BP <90 OR diastolic BP <=60 mmHg, and Age >=65. Combine the score with clinical judgement: 0–1 usually permits outpatient care, 2 warrants hospital assessment, and >=3 usually requires admission with critical-care review when appropriate.
Streptococcus pneumoniae is a leading bacterial cause of CAP; viruses commonly cause pneumonia in young children. Suspected atypical organisms (Mycoplasma pneumoniae, Legionella pneumophila) require empirical coverage with macrolides or respiratory fluoroquinolones.
Hospital-Acquired Pneumonia (HAP) develops >=48 hours after admission without incubation at admission. Choose empirical antibiotics using severity, prior cultures and local resistance data; add MRSA coverage when indicated by MRSA risk, local prevalence or severe illness.
Active pulmonary tuberculosis in the Caribbean requires prompt diagnosis via 3 morning sputum AFB smears, rapid molecular testing with GeneXpert MTB/RIF, and mycobacterial culture.
The standard first-line antitubercular regimen consists of 2 months of HRZE (Isoniazid, Rifampicin, Pyrazinamide, Ethambutol) followed by 4 months of HR (Isoniazid, Rifampicin), alongside routine Pyridoxine (vitamin B6) to prevent INH-induced peripheral neuropathy.
Lower Respiratory Infections in the Caribbean Context
Pneumonia and pulmonary tuberculosis remain prominent causes of acute morbidity, hospital admission, and mortality across the Caribbean basin. Clinical presentation is frequently modified by regional comorbidity burdens, notably poorly controlled diabetes mellitus, sickle cell disease, chronic kidney disease, and HIV infection. Clinicians practicing in regional hospitals must rapidly differentiate between typical and atypical pathogens, correctly assess disease severity to direct clinical triage, and maintain a high index of suspicion for Mycobacterium tuberculosis.
Community-Acquired Pneumonia (CAP)
Community-Acquired Pneumonia is an acute infection of the pulmonary parenchyma acquired outside of a healthcare facility. Clinically, it manifests with fever, productive cough, pleuritic chest pain, dyspnea, and signs of consolidation (dullness to percussion, bronchial breathing, and coarse inspiratory crackles).
Microbial Etiology
- Streptococcus pneumoniae (Pneumococcus): A leading bacterial cause of CAP in adults and children; viruses commonly predominate in infants and preschool children. Classically presents with abrupt high fevers, rigors, pleuritic pain, and 'rusty' (prune juice) sputum. CXR demonstrates dense lobar consolidation with air bronchograms.
- Haemophilus influenzae: Particularly prevalent among cigarette smokers, elderly patients, and those with underlying COPD or bronchiectasis.
- Atypical Pathogens:
- Mycoplasma pneumoniae: Most common in young adults and school-age children. Presents with insidious onset, dry hacking cough, low-grade fever, headache, and prominent extrapulmonary features, including autoimmune hemolytic anemia (cold agglutinins), erythema multiforme, and bullous myringitis.
- Legionella pneumophila: Transmitted via inhalation of aerosolized water from contaminated air-conditioning cooling towers, hotel water systems, or hospital plumbing. Characterized by severe multisystem disease: high remittent fever, relative bradycardia (Faget's sign), confusion/encephalopathy, watery diarrhea, hyponatremia (due to SIADH and renal wasting), and elevated hepatic transaminases. Diagnosed via urinary antigen testing.
- Chlamydophila pneumoniae: Insidious pharyngitis and hoarseness followed by prolonged bronchitis.
- Staphylococcus aureus: Often causes severe necrotizing pneumonia with cavitation and pneumatoceles following an antecedent influenza viral infection. Associated with high mortality.
- Klebsiella pneumoniae: Classically affects chronic alcohol misusers, malnourished individuals, and diabetics. Produces cavitating upper lobe consolidation with characteristic thick 'currant-jelly' sputum.
Severity Stratification: The CURB-65 Score
CURB-65 estimates adult CAP mortality risk. Combine it with clinical judgement, oxygenation, organ-support needs and comorbidities when deciding the site of care; the score alone does not determine ICU admission.
Criteria (1 Point for Each Present):
- C — Confusion: New mental confusion defined as an Abbreviated Mental Test Score (AMTS) <= 8, or new disorientation in person, place, or time.
- U — Urea: Serum urea > 7.0 mmol/L (Blood Urea Nitrogen BUN > 19 mg/dL).
- R — Respiratory Rate: Respiratory rate >= 30 breaths/min.
- B — Blood Pressure: Systolic BP < 90 mmHg OR Diastolic BP <= 60 mmHg.
- 65 — Age: Age >= 65 years.
(Note: In outpatient primary care clinics where laboratory urea is not immediately accessible, the CRB-65 score is utilized. A score of 0 indicates low risk, 1-2 warrants hospital assessment, and 3-4 requires urgent hospital admission).
CURB-65 Triage & Mortality Risk Table
| CURB-65 Score | 30-Day Mortality | Risk Category | Clinical Management Setting |
|---|---|---|---|
| 0 - 1 | < 3% | Low Risk | Outpatient care suitable; oral antibiotic therapy; primary care follow-up |
| 2 | ~9% | Intermediate Risk | Inpatient admission to general medical ward; oral or IV therapy |
| 3 | ~15% - 20% | High Risk | Urgent hospital admission; IV dual therapy; assess for ICU / HDU |
| 4 - 5 | > 30% - 40% | Severe / Critical | Urgent admission and critical-care assessment; resuscitation and IV therapy; ICU admission according to organ-support needs |
Empirical Antimicrobial Regimens for CAP
Antimicrobial selection must balance coverage for typical pyogenic bacteria with atypical pathogens.
- Outpatient CAP (CURB-65 0-1):
- First-line: Oral Amoxicillin 500 mg to 1 g TDS for 5 days.
- Penicillin-allergic or suspected atypical pathogen: Oral Doxycycline 100 mg BD or oral Clarithromycin 500 mg BD (or Azithromycin 500 mg OD).
- Inpatient Non-Severe CAP (CURB-65 2):
- Dual therapy: IV Co-amoxiclav 1.2 g TDS or oral Co-amoxiclav 500/125 mg TDS (or IV Ceftriaxone 1 g to 2 g OD) PLUS oral Clarithromycin 500 mg BD (or Azithromycin 500 mg OD).
- Alternative monotherapy: Respiratory fluoroquinolone (Levofloxacin 500 mg OD or Moxifloxacin 400 mg OD).
- Severe Inpatient CAP / ICU (CURB-65 >= 3):
- Immediate intravenous dual therapy: IV Ceftriaxone 2 g OD (or IV Co-amoxiclav 1.2 g TDS) PLUS IV Clarithromycin 500 mg BD.
- If Pseudomonas is suspected (structural lung disease, bronchiectasis): IV Piperacillin-tazobactam 4.5 g 6-8 hourly plus IV Ciprofloxacin 400 mg 12-hourly.
Hospital-Acquired Pneumonia (HAP) & Ventilator-Associated Pneumonia (VAP)
- Definition: Pneumonia developing >= 48 hours after hospital admission that was not incubating at the time of admission. Ventilator-Associated Pneumonia (VAP) arises >= 48 hours following endotracheal intubation.
- Microbiology: Shifts away from community pathogens toward multidrug-resistant hospital microflora:
- Gram-negative bacilli: Pseudomonas aeruginosa, Klebsiella pneumoniae, Enterobacter, Escherichia coli, Acinetobacter baumannii.
- Gram-positive cocci: Methicillin-Resistant Staphylococcus aureus (MRSA).
- Empirical Therapy:
- Monotherapy for low MDR risk: IV Piperacillin-tazobactam 4.5 g 6-8 hourly, or IV Ceftazidime 2 g 8-hourly, or IV Meropenem 1 g 8-hourly.
- MRSA risk or suspicion (guided by prior antibiotics/cultures, local prevalence and mortality risk): Add IV Vancomycin (initially 15–20 mg/kg every 8–12 hours in adults with normal renal function, then adjust to renal function and AUC24 400–600 mg·h/L, assuming MIC 1 mg/L) or IV Linezolid (600 mg 12-hourly).
Tuberculosis (TB) in the Caribbean
Tuberculosis remains a major public health priority across the Caribbean archipelago. Co-infection with HIV represents the single greatest risk factor for active disease, accelerating progression from latent infection to active, contagious tuberculosis.
Transmission and Pathogenesis
- Transmitted via airborne droplet nuclei (1-5 um) aerosolized during coughing or speaking by individuals with active cavitary pulmonary TB.
- Primary TB: Inhaled bacilli implant in the subpleural mid-to-lower lung fields, forming an inflammatory lesion (Ghon focus). Spread to draining hilar lymph nodes creates the classic Ghon complex. Over time, this lesion fibroses and calcifies into a Ranke complex. In immunocompetent hosts, cell-mediated immunity contains the infection within caseating granulomas (latent TB).
- Post-Primary (Reactivation) TB: Occurs when host cell-mediated immunity wanes (HIV, malnutrition, diabetes, chronic steroid use, aging). Typically localizes to the apical and posterior segments of the upper lobes due to higher ventilation-perfusion ratios and high alveolar oxygen tension (PaO2). Characterized by extensive caseous necrosis, liquefaction, cavitation, and erosion into airways.
Clinical Presentation
- Chronic productive cough persisting for > 2 to 3 weeks
- Hemoptysis (ranging from blood-streaked sputum to massive hemorrhage from eroded Rasmussen's aneurysms)
- Drenching night sweats, low-grade fevers, anorexia, and progressive unintentional weight loss ('consumption')
- Cachexia, pallor, and apical crackles on physical examination
Diagnostic Workup
- Sputum Examination: Collect three early-morning sputum specimens for Acid-Fast Bacilli (AFB) smear microscopy using Ziehl-Neelsen (ZN) or fluorochrome (auramine-rhodamine) staining.
- GeneXpert MTB/RIF Assay: The World Health Organization (WHO) recommended frontline diagnostic test. This automated, cartridge-based nucleic acid amplification test (NAAT) detects Mycobacterium tuberculosis DNA and simultaneously identifies mutations in the rpoB gene conferring rifampicin resistance within 2 hours.
- Mycobacterial Culture: Liquid media (BACTEC MGIT) and solid media (Löwenstein-Jensen). Remains the gold standard for definitive diagnosis and comprehensive phenotypic drug susceptibility testing (DST).
- Chest Radiography: Demonstrates apical patchy infiltrates, thick-walled cavitary lesions with air-fluid levels, pleural effusions, or diffuse 1-2 mm uniform 'millet-seed' nodules in miliary tuberculosis.
First-Line Antitubercular Therapy (The RIPE Regimen)
Standard therapy for drug-susceptible pulmonary tuberculosis consists of a 6-month regimen divided into two phases:
- Intensive Phase (2 Months): Rifampicin, Isoniazid, Pyrazinamide, Ethambutol (2HRZE).
- Continuation Phase (4 Months): Rifampicin and Isoniazid (4HR).
Medication Profiles, Toxicities & Clinical Monitoring
| Drug | Mechanism of Action | Major Adverse Effects | Clinical Pearls & Monitoring |
|---|---|---|---|
| Rifampicin (R) | Inhibits bacterial DNA-dependent RNA polymerase | Potent hepatic CYP450 inducer; hepatotoxicity; thrombocytopenia | Harmless orange/red discoloration of urine, sweat, saliva, and tears (warn patients); dramatically reduces levels of oral contraceptives, warfarin, and protease inhibitors |
| Isoniazid (H) | Inhibits mycolic acid cell wall synthesis | Peripheral neuropathy (pyridoxine antagonism); hepatotoxicity; drug-induced lupus | Must co-prescribe Pyridoxine (vitamin B6) 10-25 mg daily to prevent neuropathy. Discontinue if transaminases > 5x ULN (asymptomatic) or > 3x ULN with symptoms |
| Pyrazinamide (Z) | Discharges membrane potential in acidic phagosomes | Hyperuricemia (inhibits renal urate excretion); severe hepatotoxicity; polyarthralgias | Can precipitate acute gouty arthritis. The most hepatotoxic drug in the standard first-line regimen |
| Ethambutol (E) | Inhibits arabinosyl transferase (cell wall synthesis) | Retrobulbar optic neuritis (decreased visual acuity, red-green color blindness) | Test baseline visual acuity (Snellen chart) and color vision (Ishihara plates). Stop immediately if visual changes occur. May be used in young children when indicated at recommended weight-based doses, with age-appropriate monitoring |
A 71-year-old woman is evaluated in the emergency department with a 4-day history of productive cough with rust-colored sputum, right pleuritic chest pain, and high fever. Physical examination reveals bronchial breathing and dullness to percussion over the right middle lobe. Vital signs: BP 84/52 mmHg, HR 112 bpm, RR 32 breaths/min, SpO2 91% on room air, temperature 39.1°C. She is disoriented to time and place, scoring 6/10 on the Abbreviated Mental Test Score (AMTS). Laboratory evaluation reveals: serum urea 9.8 mmol/L, serum creatinine 110 umol/L, WBC 18.4 x 10^9/L. What is her CURB-65 score, and what is the most appropriate management setting?
CURB-65 score of 2; outpatient management with oral high-dose amoxicillin and close primary care follow-up
CURB-65 score of 3; admission to a short-stay observation unit with oral macrolide monotherapy
CURB-65 score of 4; inpatient admission to a general medical ward with oral ciprofloxacin
CURB-65 score of 5; urgent hospital admission with immediate intensive care / high dependency unit consultation and intravenous dual broad-spectrum antimicrobial therapy
A 42-year-old man who is HIV-positive with a CD4 count of 210 cells/uL presents to a Caribbean polyclinic with a 4-week history of productive cough, intermittent hemoptysis, drenching night sweats, and an 8 kg unintentional weight loss. A chest radiograph demonstrates bilateral apical infiltrates with a 3 cm cavitary lesion in the right upper lobe. Three sputum specimens are collected for acid-fast bacilli (AFB) smear and GeneXpert MTB/RIF testing. Which of the following statements regarding the GeneXpert MTB/RIF assay is most accurate?
It is an automated nucleic acid amplification test that detects Mycobacterium tuberculosis DNA and rifampicin resistance mutations in the rpoB gene within 2 hours
It relies on phenotypic mycobacterial culture growth and requires 4 to 6 weeks to yield definitive susceptibility results
A negative GeneXpert result completely rules out active pulmonary tuberculosis, eliminating the need for mycobacterial culture
It measures host interferon-gamma release from sensitized T lymphocytes in response to specific Mycobacterium tuberculosis antigens
A 35-year-old woman is initiated on the standard four-drug regimen (isoniazid, rifampicin, pyrazinamide, and ethambutol) for culture-confirmed active pulmonary tuberculosis. At her 4-week follow-up visit, she reports difficulty reading street signs and notes that red traffic lights appear washed-out and brownish. Visual acuity testing demonstrates a reduction from 20/20 to 20/70 bilaterally, and Ishihara color plate testing shows marked red-green color deficiency. Which drug is responsible for this adverse effect, and what is the proper management?
Isoniazid; increase the dose of pyridoxine (vitamin B6) to 100 mg daily and continue the full four-drug regimen
Ethambutol; discontinue ethambutol immediately and refer the patient for urgent ophthalmologic evaluation
Rifampicin; decrease the rifampicin dose by half and reassure the patient that optic neuritis is self-limiting
Pyrazinamide; administer intravenous allopurinol to lower serum uric acid levels and reverse optic neuropathy
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