06. Active Pulmonary Tuberculosis (TB)

Overview

Infection with Mycobacterium tuberculosis, an acid-fast–staining bacillus, is acquired by inhalation into the respiratory system with airborne particles. This review will focus on active pulmonary TB.

  • Latent TB (LTBI): a non-contagious, asymptomatic state of quiescent TB infection – the only manifestation is TST/IGRA positivity. Must rule out active pulmonary TB with symptom review and chest radiograph.
  • Active pulmonary TB:
    • Primary TB: pulmonary infection directly after inoculation. Represents ~1-5% of cases – radiographically different than reactivation TB – classically with hilar/paratracheal lymphadenopathy, lower lobe infiltrates, or pleural effusion.
    • Secondary/Reactivation TB: pulmonary infection after latent TB. Classic symptoms are subacute cough, fatigue, fever, night sweats, and weight loss. Radiographic findings depend on the host:
      • In immunocompetent hosts: apical-posterior infiltrates, cavitary disease with hilar lymphadenopathy.
      • In HIV/AIDS patients (with CD4 count < 200): diffuse disease (including miliary), mid/lower lung zone disease, hilar and mediastinal lymphadenopathy.
  • Extra-pulmonary TB: occurs via hematogenous spread from primary or reactivation TB. There is often concomitant pulmonary TB so be sure to evaluate for this possibility. Extra-pulmonary TB can present as disseminated or miliary TB, and can affect the pleura (pleural TB), bone (spinal TB = Pott’s disease), pericardium (pericarditis), bone marrow, brain (TB meningitis or tuberculoma), lymph nodes, skin (erythema induratum), GI tract (most commonly terminal ileitis), peritoneum, GU system, and joints.

Risk Factors

  • For exposure:
    • Birth, residence, or travel > 1 month in TB endemic areas
    • Employees or residents of high-risk congregation settings (correctional facilities, homeless shelters, dialysis units, nursing facilities, or hospitals)
    • Close contact of person with infectious TB
    • PWID
  • For reactivation TB:
    • Recent acquisition (e.g. within 2 years)
    • Age < 5 years
    • Immunocompromised:
      • HIV/AIDS
      • Organ transplant candidates/recipients
      • Immunosuppressive medications: prolonged corticosteroids, TNF-antagonists, chemotherapy
    • Leukemia, lymphoma, head and neck cancer
    • Abnormal CXR consistent with prior TB
    • Silicosis
    • DM
    • Renal failure requiring dialysis
  • Lifetime risk for reactivation TB (without LTBI therapy):
    • HIV-negative: 10% lifetime risk with highest risk (5%) over the first 2 years
    • HIV/AIDS: 10% per-year risk

Evaluation/Differnetial Diagnosis

  • Differential diagnosis: fungal pneumonia, bacterial lung abscess, Nocardia, non-tuberculous mycobacterial pneumonia, septic embolic disease, and malignancy
  • Patients with risk factors (above) and any of the following clinical findings should be considered for isolation and AFB testing:
    • Symptom review: cough > 2 weeks, shortness of breath, hemoptysis, night sweats, fevers, unintentional weight loss
    • History of positive TST or IGRA
    • Fever >38.5
    • Upper-lobe opacity on chest x-ray
    • Note: crackles and shortness of breath are less commonly associated with pulmonary TB
    • Note: HIV+ patients may present atypically. Have a very low threshold for ruling out TB in HIV+ patients
  • For all suspected cases of active pulmonary TB:
    • Airborne respiratory isolation
    • Evaluate for active pulmonary TB with AFB smears and NAAT (GeneXpert). Some variation in protocol by hospital: collect 2-3 AFB smear/culture (every 8 hours, including one early AM sample) and 1-2 GeneXpert samples
      • AFB smear positivity: 60% sensitivity compared to culture with one sample, an additional 10% with second sample, and additional 2% with third sample. There is decreased sensitivity in non-cavitary disease and HIV+ patients
      • Culture: gold standard of diagnosis, allows for determining drug susceptibility
      • GeneXpert has a sensitivity of >95% in smear-positive samples and ~60% in smear-negative culture-positive samples (can increase this to 70% with a second Xpert test). It also can detect rifampin resistance
  • Consider empiric treatment for patients in whom clinical suspicion is high
  • TST and IGRA cannot distinguish between latent and active pulmonary TB. Either can be negative in 25% of patients with active infection

Management

  • If four-drug RIPE (rifampin, isoniazid, pyrazinamide, and ethambutol) therapy is being considered, consult Infectious Diseases
  • All patients on isoniazid should also receive pyridoxine (Vitamin B6)
  • All culture-confirmed cases or suspected cases started on anti-TB therapy should be reported to the Department of Public Health

Key Points

  • Fluoroquinolones should be avoided in patients with clinical suspicion of TB who are not on therapy to avoid development of resistance from TB monotherapy
  • An HIV specialist should be consulted when initiating treatment for TB if a patient is on ART as significant drug interactions with rifampin and ART may exist

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Key Words: Tuberculosis, Mycobacterium tuberculosis