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Tuberculosis (TB)

BASICS

  • Definition: Active infection caused by Mycobacterium tuberculosis complex (MTB, M. bovis, M. africanum)
  • Forms:
  • Pulmonary TB (85%)
  • Extrapulmonary TB: miliary (disseminated), CNS (meningitis), lymphadenitis (scrofula), abdominal, pericardial, osteoarticular
  • Transmission: Inhalation of airborne bacilli from an individual with active pulmonary TB
  • Pathogenesis:
  • Bacilli enter alveoli → phagocytosed by macrophages → spread via lymphatics and bloodstream
  • Granuloma (tubercle) formation through cell-mediated immunity
  • May progress to caseous necrosis and cavitation
  • Outcome: eradication, latent infection (LTBI), or progression to active TB

EPIDEMIOLOGY

Metric Global (2021) United States (2022)
New Cases 10.6 million (134/100,000) 8,300 (2.5/100,000)
HIV-Associated TB 7% of cases –
TB Deaths 1.6 million –
Notable Trend Rising U.S. case rate after 10-year decline 71% cases in foreign-born

RISK FACTORS

For Infection

  • Close contact with TB case
  • Congregate living (prisons, shelters)
  • Homelessness, poverty
  • Healthcare workers

For Reactivation

  • HIV, immunosuppression
  • Diabetes, renal failure, malignancy
  • Malnutrition, smoking, IV drug use
  • Children <5 years
  • Recent infection (<2 years)
  • Systemic corticosteroids

COMMONLY ASSOCIATED CONDITIONS

  • HIV
  • Malignancy
  • Other immunosuppressive states

CLINICAL PRESENTATION

General Symptoms

  • Fever, night sweats
  • Weight loss
  • Fatigue, malaise
  • Lymphadenopathy
  • Arthralgia

Pulmonary TB

  • Chronic cough >2–3 weeks
  • Hemoptysis
  • Pleuritic chest pain

Abdominal TB

  • “Doughy” abdomen
  • Abdominal mass or pain
  • May mimic acute abdomen

PHYSICAL EXAM

  • Often normal
  • May show cachexia, lymphadenopathy, pulmonary findings
  • Poor weight gain in children

DIFFERENTIAL DIAGNOSIS

  • Pulmonary TB: pneumonia, lung cancer, fungal infections, sarcoidosis
  • Extrapulmonary TB: leishmaniasis, lymphoma, cat-scratch disease, autoimmune conditions

DIAGNOSTIC EVALUATION

Screening Tests

Test Preferred In
TST (PPD) Children <5 years
IGRA Age >5, BCG-vaccinated

TST and IGRA cannot differentiate active TB from LTBI

TST Interpretation

Induration Interpretation
≥5 mm HIV+, close TB contact, immunosuppressed
≥10 mm Recent immigrant, IV drug use, children <5 yrs
≥15 mm No risk factors

Confirmatory Tests for Active TB

Test Utility
AFB Smear and Culture (x3 sputum samples) Gold standard
NAAT / Xpert MTB/RIF Rapid detection, rifampin resistance
Chest X-ray / CT Primary TB: infiltrates, hilar LAD; Tree-in-bud sign on CT
Biopsies (CSF, lymph node, bone marrow) For extrapulmonary TB
Blood Work CBC, LFTs, HIV, Hep B/C

TREATMENT OF ACTIVE TB

General Measures

  • Initiate therapy if clinical suspicion is high
  • Airborne isolation until:
  • 2–3 weeks of therapy
  • Clinical improvement

  • 3 consecutive negative AFB smears

  • Directly Observed Therapy (DOT) recommended

  • Notify public health authorities

Standard Regimens

Regimen 1 (Preferred)

Phase Drugs Duration
Intensive INH + RIF + PZA + EMB 8 weeks
Continuation INH + RIF 18 weeks

Regimen 2 (Shorter, 4-month)

  • INH + RPT + MOX + PZA (8 weeks), then INH + RPT + MOX (9 weeks)

Use only in patients >12 yrs, >40 kg, drug-susceptible TB, no HIV or cavitation

Regimens 3–5

  • Modified frequencies (3x/week or 2x/week)
  • Caution: Not recommended for patients with HIV or cavitary disease

Special Populations

Pregnancy

  • Safe: INH + RIF + EMB ± PZA
  • Supplement with pyridoxine (25–50 mg/day)
  • Breastfeeding allowed with treatment

Children

  • Often more severe disease
  • Use same 4-drug regimen
  • DOT mandatory

HIV-Positive

  • Start TB treatment first
  • Initiate ART within 2 weeks (CD4 <50) or within 8 weeks (CD4 ≥50)
  • Monitor for IRIS

FOLLOW-UP AND MONITORING

Test Frequency
AFB smear/culture Monthly until 2 consecutive negatives
LFTs Monthly if liver disease, pregnancy, alcohol use
Vision (EMB >2 months or >20 mg/kg) Monthly red-green screening
CXR After 2 months
  • Missed doses: may require restart or extension of regimen
  • Reassess sensitivity if culture positive after 2 months

COMPLICATIONS

  • Cavitary lesions
  • Drug-induced hepatitis
  • Multidrug-resistant TB (MDR-TB)
  • Extensively drug-resistant TB (XDR-TB)
  • IRIS in HIV+ individuals starting ART
  • Secondary infections

SECOND-LINE THERAPIES

  • Fluoroquinolones, Aminoglycosides, Pretomanid
  • Use in:
  • Drug resistance
  • Drug intolerance

PUBLIC HEALTH AND REFERRAL

  • Mandatory reporting of active TB to local health authorities
  • Consult infectious disease for:
  • MDR/XDR-TB
  • HIV coinfection
  • Pregnancy
  • Pediatric TB

CODES

  • ICD-10:
  • A15.0 – Tuberculosis of lung
  • A15.9 – Respiratory TB, unspecified
  • A19.9 – Miliary TB, unspecified

CLINICAL PEARLS

  • TB is curable with full adherence.
  • Children and elderly often present atypically.
  • TST and IGRA cannot distinguish active TB from LTBI.
  • Public health notification is mandatory for all active TB cases.
  • DOT improves outcomes and prevents resistance.