2.3 Community-Acquired Pneumonia & Pulmonary Tuberculosis
Key Takeaways
- Streptococcus pneumoniae is the most common cause of Community-Acquired Pneumonia (CAP), while atypical pathogens (Mycoplasma, Legionella) present with extrapulmonary symptoms and require macrolides or respiratory fluoroquinolones.
- The CURB-65 score stratifies CAP mortality risk (Confusion, Urea >7 mmol/L, Respiratory rate ≥30, BP <90/60, Age ≥65): scores 0-1 are managed outpatient, score 2 inpatient ward, and scores ≥3 require intensive care assessment.
- Under India's National Tuberculosis Elimination Program (NTEP), CBNAAT (GeneXpert MTB/RIF) is the mandatory primary diagnostic test for suspected pulmonary TB to confirm M. tuberculosis complex and detect Rifampicin resistance upfront.
- Drug-sensitive pulmonary TB is treated with a 6-month regimen (2 months Intensive HRZE + 4 months Continuation HRE), with strict awareness of drug toxicities: Isoniazid (peripheral neuropathy - prevent with Vit B6), Rifampicin (orange secretions), Pyrazinamide (hyperuricemia/hepatotoxicity), and Ethambutol (optic neuritis/color blindness).
Community-Acquired Pneumonia & Pulmonary Tuberculosis
1. Community-Acquired Pneumonia (CAP) Pathophysiology & Etiology
Community-Acquired Pneumonia (CAP) is an acute infection of the pulmonary parenchyma acquired outside of hospital or healthcare facilities.
Etiological Spectrum
| Category | Causative Pathogens | Clinical & Radiologic Features |
|---|---|---|
| Typical Bacterial | Streptococcus pneumoniae (most common ~50%), Haemophilus influenzae, Moraxella catarrhalis, Staphylococcus aureus | Sudden onset high fever, rigors, productive cough with rusty sputum (S. pneumoniae), lobar consolidation on chest X-ray. |
| Atypical Bacterial | Mycoplasma pneumoniae, Legionella pneumophila, Chlamydia pneumoniae | Insidious onset, dry cough, prominent extrapulmonary symptoms (headache, myalgias, low grade fever). Interstitial / patchy infiltrates ("walking pneumonia"). |
| Viral | Influenza A/B, SARS-CoV-2, Respiratory Syncytial Virus (RSV) | Diffuse bilateral interstitial infiltrates, prominent systemic flu-like symptoms. |
Key Pathogen Associations (UPSC CMS High-Yield)
- Klebsiella pneumoniae: Alcoholics, diabetics; presents with "currant jelly" sputum and upper lobe cavitation (bulging fissure sign).
- Staphylococcus aureus: Secondary bacterial pneumonia following Influenza virus infection; prone to causing cavitary lesions, pneumatoceles, and empyema.
- Mycoplasma pneumoniae: Young adults in dormitories/military camps; associated with erythema multiforme, cold agglutinin autoimmune hemolytic anemia (IgM), and bullous myringitis.
- Legionella pneumophila: Exposure to contaminated air conditioning cooling towers or water plumbing; presents with high fever, relative bradycardia (Faget sign), hyponatremia, diarrhea, and confusion.
2. Risk Stratification: The CURB-65 Score
The CURB-65 criteria predict 30-day mortality and determine the appropriate site of care (Outpatient vs Inpatient Ward vs ICU):
| Criterion | Description | Points |
|---|---|---|
| C | Confusion (Abnormal mental status test score $\le 8$ or new disorientation) | 1 |
| U | Urea (Blood Urea Nitrogen $>19 \text{ mg/dL}$ or Serum Urea $>7 \text{ mmol/L}$) | 1 |
| R | Respiratory Rate $\ge 30 \text{ breaths/min}$ | 1 |
| B | Blood Pressure (Systolic $<90 \text{ mmHg}$ OR Diastolic $\le 60 \text{ mmHg}$) | 1 |
| 65 | Age $\ge 65 \text{ years}$ | 1 |
CURB-65 Management Triage
| Total Score | Mortality Risk | Recommended Management Disposition |
|---|---|---|
| 0 – 1 | Low (<3%) | Outpatient care with oral antimicrobial therapy. |
| 2 | Moderate (9%) | Inpatient hospital ward admission or close outpatient monitoring. |
| $\ge 3$ | High (15–40%) | Severe CAP: Urgent inpatient hospitalization; evaluate for ICU admission (especially if score 4–5). |
3. Empiric Antimicrobial Treatment Protocols
Treatment must be initiated promptly based on setting and national/international guidelines:
- Outpatient (Healthy, no comorbidity): Oral Amoxicillin $1 \text{ g}$ tid OR Azithromycin $500 \text{ mg}$ day 1 then $250 \text{ mg}$ daily OR Doxycycline $100 \text{ mg}$ bid.
- Outpatient (With Comorbidities - COPD, DM, CKD, heart disease): Oral Amoxicillin/Clavulanate + Macrolide (Azithromycin) OR Monotherapy with Respiratory Fluoroquinolone (Levofloxacin $750 \text{ mg}$ daily or Moxifloxacin $400 \text{ mg}$ daily).
- Inpatient Non-ICU Ward: IV Beta-lactam (Ceftriaxone $1-2 \text{ g}$ daily or Cefotaxime) + IV/Oral Macrolide (Azithromycin) OR IV Respiratory Fluoroquinolone (Levofloxacin).
- Inpatient ICU (Severe CAP): IV Beta-lactam (Ceftriaxone $2 \text{ g}$ daily or Piperacillin-Tazobactam) + IV Azithromycin OR IV Levofloxacin. Add IV Vancomycin or Linezolid if MRSA is suspected.
4. Pulmonary Tuberculosis (TB) & NTEP Guidelines
Tuberculosis is caused by Mycobacterium tuberculosis, an obligate aerobic, acid-fast bacillus (AFB).
Clinical Manifestations
- Constitutional Symptoms: Low-grade fever with characteristic evening rise of temperature, night sweats, anorexia, weight loss.
- Pulmonary Symptoms: Chronic cough $>2 \text{ weeks}$, mucopurulent sputum production, hemoptysis, pleuritic chest pain.
- Radiology: Primary TB presents with Ghon focus (subpleural parenchymal lesion) + lymphadenopathy = Ghon Complex. Secondary/Reactivation TB demonstrates apical and subapical cavitary lesions in upper lobes (high $PO_2$).
Diagnostic Cascade (National Tuberculosis Elimination Program - NTEP India)
Under NTEP guidelines, sputum microscopy is replaced by rapid molecular diagnostics as the primary test:
- CBNAAT (Cartridge Based Nucleic Acid Amplification Test / GeneXpert MTB/RIF): Mandatory initial diagnostic test for all presumptive TB cases.
- Simultaneously detects M. tuberculosis complex DNA and mutations in the rpoB gene conferring Rifampicin resistance within 2 hours.
- Sputum Smear Microscopy: Ziehl-Neelsen (ZN) staining or Auramine-O Fluorescent staining (detects acid-fast bacilli; requires $\ge 10,000 \text{ bacilli/mL}$).
- Line Probe Assay (LPA): Used for rapid second-line drug susceptibility testing (Fluoroquinolones, Injectable drugs).
- Liquid Culture (MGIT): Gold standard for confirmation and definitive DST.
5. NTEP Anti-Tubercular Therapy (ATT) Regimens
Treatment of Drug-Microbiologically Sensitive Pulmonary TB consists of Fixed-Dose Combination (FDC) tablets administered daily according to weight bands:
- Intensive Phase (IP) - 2 Months (2 HRZE): Daily Isoniazid (H), Rifampicin (R), Pyrazinamide (Z), Ethambutol (E). Rapidly kills actively dividing bacilli and clears sputum.
- Continuation Phase (CP) - 4 Months (4 HRE): Daily Isoniazid (H), Rifampicin (R), Ethambutol (E). Eliminates persistent dormant bacilli to prevent relapse.
NTEP Update Note: Ethambutol is included in the Continuation Phase (4 HRE) under NTEP to protect against monotherapy in cases of undetected primary isoniazid resistance.
6. High-Yield Adverse Effects of First-Line Anti-TB Drugs
| Drug | Primary Mechanism of Action | Major Adverse Effects & Toxicity Profiles | Clinical Pearls & Antidotes |
|---|---|---|---|
| Isoniazid (H) | Inhibits mycolic acid synthesis | Peripheral Neuropathy (due to Vitamin B6 deficiency), Hepatotoxicity, Drug-induced Lupus | Co-administer Pyridoxine (Vitamin B6 10-25 mg/day) to prevent neuropathy. |
| Rifampicin (R) | Inhibits bacterial DNA-dependent RNA polymerase | Orange-red discoloration of bodily fluids (urine, tears, sweat), Hepatotoxicity, Strong CYP450 inducer, Thrombocytopenia | Reassure patient regarding orange secretions. Interacts with oral contraceptives and Warfarin. |
| Pyrazinamide (Z) | Disruption of membrane potential & energy metabolism | Hyperuricemia (causes arthralgia/gout), Most Hepatotoxic first-line drug | Avoid in severe liver disease or acute gouty arthritis. |
| Ethambutol (E) | Inhibits arabinosyl transferase (cell wall synthesis) | Retrobulbar Optic Neuritis (decreased visual acuity, red-green color blindness, central scotoma) | Bacteriostatic (others are bactericidal). Test visual acuity & color vision baseline; Contraindicated in young children. |
| Streptomycin (S) | Inhibits 30S ribosomal subunit protein synthesis | Ototoxicity (vestibular damage, irreversible hearing loss), Nephrotoxicity | Second-line injectable. Avoid in pregnancy (causes fetal congenital deafness). |
A 68-year-old male with a history of chronic obstructive pulmonary disease presents to the clinic with fever, productive cough, and shortness of breath. On exam, he is confused (AMTS 6/10), blood pressure is 84/52 mmHg, pulse 110 bpm, respiratory rate 32 breaths/min, and blood urea nitrogen is 28 mg/dL (Urea 10 mmol/L). What is his CURB-65 score and the most appropriate management disposition?
A 34-year-old male receiving standard fixed-dose anti-tubercular therapy (ATT) under NTEP for pulmonary tuberculosis presents to the clinic complaining of difficulty distinguishing red and green traffic lights and progressive blurring of vision in both eyes. Which anti-tubercular medication is responsible for this adverse effect?
A 22-year-old college student presents with a 10-day history of low-grade fever, dry hacking cough, headache, and generalized malaise. Chest X-ray demonstrates patchy bilateral interstitial infiltrates despite mild physical lung signs. Laboratory testing reveals elevated cold agglutinin titers (IgM). Which of the following is the most appropriate empirical antibiotic therapy?
Under the National Tuberculosis Elimination Program (NTEP) guidelines in India, what is the mandatory primary initial diagnostic test recommended for all patients with presumptive pulmonary tuberculosis?