Tuberculosis

Overview and Pathogenesis of Tuberculosis

• Definition and Nature of the Disease: Tuberculosis (TB) is a contagious, chronic bacterial infection. While it primarily affects the lungs, it is capable of involving almost any part of the body.
• Etiological Agent: In humans, the disease is primarily caused by Mycobacterium tuberculosis.
  • Morphology: These organisms are long, slender, straight, or curved rods.
  • Characteristics: They are highly aerobic organisms and are classified as acid-fast bacilli (AFB).
• Transmission and Entry:
  • Transmission Mechanism: The bacilli are transmitted almost exclusively within aerosol droplets. These droplets are produced when an individual with active TB coughs, sneezes, or laughs.
  • Suspension: TB bacilli are highly resilient and can remain suspended in the air for several hours after a cough or sneeze.
  • Portals of Entry: The bacteria can enter the body via the respiratory tract, the gastrointestinal tract, or through an open wound in the skin.
  • Risk Factors: Individuals living in closed, small spaces are at a significantly higher risk of transmission.
• Recent Clinical Incident: A report from $9/27/14$ noted a plague at an El Paso hospital where an employee exposed hundreds of infants to the disease. Consequently, five babies tested positive for TB infection.

Epidemiology and Historical Context

• Global Prevalence: Approximately one-third ($1/3$) of the world's population is currently infected with latent TB.
  • Latent TB Definition: Individuals are infected with the bacteria but are not clinically ill and cannot transmit the disease to others.
• United States Statistics (CDC Data):
  • In $2012$, there were $9945$ new cases of TB reported in the U.S., which was the lowest number since reporting began in $1953$.
• Historical Trends:
  • Between $1986$ and $1992$, there was a notable increase in TB cases.
  • Contributing Factors: This spike was attributed to increased immigration from endemic areas, the rise of HIV, and the increased use of immunosuppressant drugs.

Anatomic Alterations of the Lungs

• Primary Tuberculosis: This is the initial infection stage.
  • When bacilli are inhaled, they multiply over a $3$ to $4$ week period, triggering an inflammatory response.
  • Macrophages migrate to the site and engulf the bacilli, though they do not always fully kill them.
• Postprimary Tuberculosis: Also known as Reactivation TB, Reinfection TB, or Secondary TB.
• Disseminated Tuberculosis: Also referred to as Extrapulmonary TB, Miliary TB, or Tuberculosis-disseminated.
• Common Pathological Changes (Mainly Postprimary):
  • Alveolar consolidation.
  • Alveolar-capillary destruction.
  • Formation of caseous tubercles or granulomas.
  • Cavity formation (cavitation).
  • Fibrosis and secondary calcification of the lung parenchyma.
  • Distortion and dilation of the bronchi.
  • Increased bronchial airway secretions.
• Disease Progression:
  • Early primary infection leads to the development of caseous tubercles.
  • Progression involves the cavitation of these tubercles and the development of new primary lesions, often in subpleural locations.
  • Advanced stages result in severe, permanent lung destruction.

Diagnostic Procedures and Interpretation

• Mantoux Tuberculin Skin Test:
  • Consists of an intradermal injection of a small amount of purified protein derivative ($PPD$) of the tuberculin bacillus.
  • Interpretation based on Induration (Swelling Size, not redness):
    • Negative: A wheal less than $5\,mm$.
    • Suspicious: A wheal measuring $5\,mm$ to $9\,mm$.
    • Positive: A wheal of $10\,mm$ or greater is considered sound evidence of recent or past infection or disease.
• Specific PPD Guidelines for Populations:
  • $5\,mm$ Threshold: Positive for HIV-positive groups or those in recent close contact with an active TB case.
  • $10\,mm$ Threshold: Positive for IV drug abusers, medically underserved populations, healthcare workers, and residents of long-term care facilities.
  • $15\,mm$ Threshold: Positive for the general public without known risk factors.
• Acid-fast Staining:
  • Ziehl-Neelsen Stain: Reveals bright red acid-fast bacilli against a blue background.
  • Fluorescent Acid-fast Stain: Reveals luminescent yellow-green bacilli against a dark brown background.
• Sputum Culture:
  • Necessary to differentiate M. tuberculosis from nontuberculous strains (e.g., Mycobacterium avium or Mycobacterium kansasii, which are often associated with COPD).
  • Identify drug-resistant bacilli and their antibiotic sensitivity.
  • M. tuberculosis grows slowly; it can take up to $6\,weeks$ for colonies to appear in culture.
• QuantiFERON-TB Gold Test (QFT-G):
  • Approved by the FDA in $2005$.
  • A whole-blood test used for diagnosing M. tuberculosis infection, including latent cases.
  • Results are typically available after $24\,hours$.

Clinical Data and Physical Examination

• Bedside Physical Examination Findings:
  • General Constitutional Symptoms: Progressive fatigue, malaise, anorexia, weight loss, and night sweats.
  • Temperature: Low-grade fever, often occurring in the late afternoon.
  • Respiratory Symptoms: Pleuritic chest pain, decreased chest expansion, cyanosis, and digital clubbing.
  • Cough: Chronic, productive cough; hemoptysis is seen in advanced states.
  • Signs of Heart Failure (Right-sided): Peripheral edema, venous distention (distended neck veins), pitting edema, and an enlarged, tender liver.
• Chest Assessment Findings:
  • Increased tactile and vocal fremitus.
  • Dull percussion note.
  • Bronchial breath sounds.
  • Crackles, rhonchi, and wheezing.
  • Pleural friction rub (if the infection extends to the pleural surface).
  • Whispered pectoriloquy.

Radiologic Findings (Chest Radiograph)

• Common Imaging Signs:
  • Increased opacity.
  • Ghon Nodule: A small, circumscribed lesion.
  • Ghon Complex: Involvement of the Ghon nodule and the associated lymph nodes.
  • Cavitation: Left upper lobe cavities are common in reactivation TB; these may contain air-fluid levels.
  • Pleural effusion and localized pleural thickening.
  • Calcification and fibrosis.
  • Retraction of lung segments or lobes.
  • Right ventricular enlargement (Cor Pulmonale).
  • Miliary TB: Characterized by widespread, uniformly distributed fine nodulation throughout the lung.

Medical and Pharmacologic Management

• General Strategy: Pharmacological treatment typically consists of $2$ to $4$ drugs administered over a period of $6$ to $9$ months (up to $12\,months$ in some instances).
• 6-Month Treatment Protocol:
  • Induction Phase (First $2\,months$): Daily dose of isoniazid ($INH$), rifampin, pyrazinamide, and either ethambutol or streptomycin.
  • Continuation Phase (Next $4\,months$): Daily or twice-weekly doses of isoniazid and rifampin.
• 9-Month Treatment Protocol:
  • Initial Phase (First $1$ to $2\,months$): Daily dose of isoniazid and rifampin.
  • Continuation Phase: Twice-weekly isoniazid and rifampin until the full $9\,month$ period is reached.
• First-Line Agents:
  • Isoniazid ($INH$): Considered the most effective first-line antituberculosis agent.
  • Rifampin (Rifadin): A bactericidal agent most commonly used in conjunction with isoniazid.
• Clinical Management Requirements:
  • Respiratory isolation must be maintained until sputum studies (collected as $3$ specimens on different days) are negative.
  • Decreased physical activity.
  • Treatment is frequently handled on an outpatient basis.

Respiratory Care Treatment Protocols

• Standard Protocols: In cases of clinical deterioration or specific symptomatic needs, the following protocols are utilized:
  • Oxygen Therapy Protocol: To manage hypoxemia.
  • Bronchopulmonary Hygiene Therapy Protocol: To manage increased secretions and airway clearance.
  • Mechanical Ventilation Protocol: Employed in cases of severe respiratory failure or lung destruction.