Pulmonary · PANCE / PANRE

Tuberculosis (Active and Latent)

Written & clinically reviewed by Ryan Busch, PA-C · Updated August 2026 · Report an error

Mycobacterium tuberculosis infection — active disease or asymptomatic latent infection (LTBI).

Also known as: TB, tuberculosis, latent TB, LTBI, active TB, Mycobacterium tuberculosis, miliary TB

Overview

Infection with Mycobacterium tuberculosis complex. Latent TB infection (LTBI): asymptomatic, non-contagious, positive immunologic test, no clinical/radiographic disease. Active TB: symptomatic disease, often pulmonary, contagious; may be primary or reactivation.

Epidemiology

Globally ~10 million new cases and ~1.3 million deaths annually. In the US, >85% of cases occur in non-US-born persons or those born in high-burden countries. HIV coinfection accelerates progression. Drug-resistant TB (MDR, XDR) is a global challenge.

Try two board-style Tuberculosis questions

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Question 1PulmonaryMedium
A 58-year-old man with a 40-pack-year smoking history and chronic obstructive pulmonary disease reports several weeks of drenching night sweats, a 20-lb unintentional weight loss, and blood-streaked sputum. Chest imaging shows a new 2-cm cavitary lesion in the right upper lobe. He is hemodynamically stable and afebrile in the clinic. Which of the following is the most appropriate next step in management?
  • AEmpiric antibiotics for pneumonia
  • BCT-guided transthoracic lung biopsy
  • CEmpiric systemic antifungal therapy
  • DAFB sputum smear and culture × 3
Reveal answer & full explanation
Correct answer: D — AFB sputum smear and culture × 3
  • AEmpiric antibiotics for pneumonia
  • BCT-guided transthoracic lung biopsy
  • CEmpiric systemic antifungal therapy
  • DAFB sputum smear and culture × 3✓

Why AFB sputum smear and culture × 3 is correct

  • A cavitary right-upper-lobe lesion with night sweats, weight loss, and hemoptysis is the classic presentation of reactivation pulmonary tuberculosis, which must be excluded before anything else.
  • The first step is to collect acid-fast bacilli (AFB) sputum smears and cultures (three specimens) and place the patient in airborne isolation to protect staff and other patients.
  • Smear plus culture, with nucleic acid amplification testing, establishes the diagnosis and drug susceptibility; it is non-invasive, inexpensive, and carries immediate public-health implications.

Why the others are wrong

  • Empiric antibiotics for pneumonia — a subacute cavitary lesion with weeks of constitutional symptoms is not acute bacterial pneumonia; premature closure on the most common cause of a lung infiltrate that also delays TB isolation.
  • CT-guided transthoracic lung biopsy — although malignancy is on the differential in a smoker, an invasive biopsy before active TB is excluded risks aerosolizing organisms and exposing staff; it is a later step, a right-concern-wrong-sequence error.
  • Empiric systemic antifungal therapy — there is no host risk factor or exposure history pointing to an endemic or invasive fungal infection; it buzzword-matches 'cavitary lesion' without justification.
Question 2PulmonaryEasy
A 30-year-old female has a positive purified protein derivative (PPD) (18mm induration) with no symptoms and a normal chest X-ray. She was born in a tuberculosis (TB)-endemic country and has never been treated. She has no immunocompromising conditions. Which of the following is the most appropriate next step?
  • AIsoniazid plus rifapentine for 12 weeks
  • BNo pharmacologic therapy indicated
  • CFour-drug rifampin/isoniazid/pyrazinamide/ethambutol regimen
  • DRepeat tuberculin skin test in 6 months
Reveal answer & full explanation
Correct answer: A — Isoniazid plus rifapentine for 12 weeks
  • AIsoniazid plus rifapentine for 12 weeks✓
  • BNo pharmacologic therapy indicated
  • CFour-drug rifampin/isoniazid/pyrazinamide/ethambutol regimen
  • DRepeat tuberculin skin test in 6 months

Why isoniazid plus rifapentine for 12 weeks is correct

  • A positive tuberculin skin test (TST) or interferon-gamma release assay (IGRA) with a normal chest X-ray and no symptoms represents latent tuberculosis infection (LTBI), not active tuberculosis (TB).
  • Treatment of LTBI reduces reactivation risk by 90%.
  • The preferred regimen is 3HP: isoniazid plus rifapentine once weekly for 12 weeks — preferred for best adherence.
  • An alternative is isoniazid (INH) for 9 months.
  • Active TB must be ruled out before starting treatment (chest X-ray, symptom review).
  • Pyridoxine (B6) should be given with INH to prevent peripheral neuropathy.

Why the others are wrong

  • No pharmacologic therapy indicated — a positive PPD in a person from a TB-endemic country represents latent TB infection, which warrants treatment to prevent reactivation; withholding therapy leaves a 5–10% lifetime reactivation risk.
  • Four-drug rifampin/isoniazid/pyrazinamide/ethambutol regimen — RIPE is the treatment for active TB; with no symptoms and a normal chest X-ray this is latent infection, and four-drug therapy would be excessive and unnecessarily toxic.
  • Repeat tuberculin skin test in 6 months — the diagnosis is already established by the 18 mm induration, so re-testing only delays treatment; a once-positive TST stays positive and would not change management.

Additional high-yield points

  • Interferon-gamma release assay (IGRA) such as QuantiFERON is preferred over TST for Bacillus Calmette-Guerin (BCG)-vaccinated individuals, as BCG vaccination can cause false-positive TST results.
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Risk factors

  • Birth or residence in high-prevalence country, recent travel
  • Close contact with active pulmonary TB case
  • HIV/AIDS, immunosuppression (TNF-alpha inhibitors, transplant, chemotherapy, chronic corticosteroids)
  • Diabetes mellitus, end-stage renal disease, silicosis
  • Healthcare workers, prison/shelter exposure, IV drug use
  • Children <5 years and elderly
  • Malnutrition, alcohol use disorder, smoking

Pathophysiology

Inhaled aerosolized droplet nuclei reach alveoli, ingested by alveolar macrophages. Most contain infection in granulomas (latent). With reduced immunity, dormant bacilli reactivate → caseating granulomas, cavitation, hematogenous spread (miliary). Lifetime reactivation risk ~5-10% (general), ~10%/year with untreated HIV.

Clinical presentation

Symptoms

  • LTBI: asymptomatic by definition
  • Active pulmonary TB: chronic cough >3 weeks (productive, may be hemoptysis), drenching night sweats, fevers, weight loss, anorexia, fatigue
  • Pleuritic chest pain if pleural involvement
  • Extrapulmonary TB: lymphadenitis (scrofula), TB meningitis, Pott disease (spinal), genitourinary, peritoneal, miliary

Signs / physical exam

  • Often nonspecific exam early in disease
  • Fever, cachexia, post-tussive crackles, amphoric breath sounds over cavities
  • Lymphadenopathy, hepatosplenomegaly (miliary)

Classic findings

Apical/posterior upper lobe or superior segment of lower lobe cavitary disease (reactivation); hilar lymphadenopathy + middle/lower lobe infiltrate (primary); miliary nodules (2-3 mm) on CXR (disseminated).

Differential diagnosis

  • Community-acquired pneumonia — Acute onset, lobar consolidation, responds to standard antibiotics within days
  • Lung cancer — Mass lesion in smoker, weight loss, hemoptysis; biopsy distinguishes
  • Non-tuberculous mycobacteria (M. avium complex, M. kansasii) — Older women with bronchiectasis ('Lady Windermere'), cavitary disease in COPD; AFB+ but TB-specific NAAT negative
  • Fungal pneumonia (histoplasmosis, coccidioidomycosis, blastomycosis) — Geographic exposure (Mississippi/Ohio valley, Southwest, Great Lakes); serology and fungal cultures
  • Sarcoidosis — Bilateral hilar lymphadenopathy without parenchymal cavitation, non-caseating granulomas, elevated ACE
  • Lung abscess — Air-fluid level on CXR, putrid sputum, polymicrobial flora
  • Pulmonary aspergillosis — Aspergilloma in pre-existing cavity (often TB), positive Aspergillus IgG/galactomannan

Diagnostic workup

Diagnostic criteria

LTBI: positive TST (induration ≥5/10/15 mm cutoff based on risk) or positive IGRA + no active disease on imaging/clinical evaluation. Active TB: clinical findings + positive AFB smear/NAAT/culture from respiratory or other site.

Labs

  • LTBI: tuberculin skin test (TST/PPD) OR interferon-gamma release assay (IGRA — QuantiFERON, T-SPOT)
  • Active TB: 3 sputum samples for AFB smear, culture (gold standard, 6-8 weeks), and NAAT (Xpert MTB/RIF, rapid)
  • HIV test on every TB patient
  • CBC, CMP, hepatitis serologies, baseline LFTs before treatment
  • Drug susceptibility testing on positive culture

Imaging

  • CXR — primary: hilar adenopathy, middle/lower infiltrate, Ghon complex; reactivation: apical/posterior cavitary lesions; miliary: 2-3 mm nodules diffuse
  • CT chest if CXR equivocal or to characterize disease
  • MRI brain/spine if neurologic/spinal TB suspected

Diagnostic algorithm

TST IndurationConsidered Positive If…
≥5 mmHIV+, recent contact with active TB, fibrotic CXR consistent with prior TB, organ transplant, immunosuppression (≥15 mg/d prednisone × 1 mo, TNF inhibitors)
≥10 mmRecent immigrant (<5 y) from high-prevalence country, IVDU, healthcare workers, prison/shelter residents, children <5, mycobacterial lab workers, diabetes/CKD/silicosis
≥15 mmAny person with no known risk factors
Mantoux tuberculin skin test (TST) cutoffs for positivity by risk category (CDC).

Treatment

First-line

  • LTBI (CDC 2020 preferred shorter regimens): isoniazid + rifapentine weekly × 12 weeks (3HP, DOT); OR rifampin daily × 4 months (4R); OR isoniazid + rifampin daily × 3 months (3HR)
  • LTBI alternative: isoniazid daily × 6 or 9 months (older standard; longer, more hepatotoxicity)
  • Active drug-susceptible TB (RIPE × 2 months intensive phase): rifampin (R) + isoniazid (H/INH) + pyrazinamide (Z/PZA) + ethambutol (E)
  • Continuation phase × 4 months: rifampin + isoniazid (HR) — total 6 months
  • Always add pyridoxine (vitamin B6) 25-50 mg daily with isoniazid to prevent peripheral neuropathy
  • Directly observed therapy (DOT) recommended to ensure adherence and prevent resistance
  • Report all cases to public health department; contact tracing

Second-line / adjunct

  • Drug-resistant TB: MDR (resistant to INH + RIF) — bedaquiline-containing regimens (BPaL: bedaquiline + pretomanid + linezolid × 6 months, per 2022 WHO update)
  • XDR (additional resistance to fluoroquinolones and a second-line injectable): individualized regimens with newer agents
  • TB meningitis: extend therapy to 9-12 months + adjunctive corticosteroids (dexamethasone) to reduce mortality and neurologic sequelae
  • Pott disease (spinal TB): 6-9 months + surgical consultation for spinal instability or cord compression
  • HIV coinfection: start ART within 2-8 weeks of TB therapy (sooner if CD4 <50); watch for IRIS
  • Drug toxicities: hepatotoxicity (especially INH, RIF, PZA — monitor LFTs), optic neuritis (ethambutol — baseline and monthly vision), hyperuricemia/gout (PZA), orange body fluids (rifampin), drug-drug interactions (rifampin is potent CYP3A4 inducer)

Complications

  • Cavitary disease, hemoptysis (Rasmussen aneurysm), pneumothorax
  • Miliary/disseminated TB, TB meningitis, Pott disease
  • Multidrug-resistant and extensively drug-resistant TB
  • Aspergilloma formation in old cavities
  • Constrictive pericarditis, bronchiectasis (post-TB)
  • Drug toxicities — DILI, peripheral neuropathy, optic neuritis

PANCE pearls

  • Reactivation TB favors apical/posterior segments (higher O2 tension); primary TB favors middle/lower lobes with hilar adenopathy.
  • Mantoux interpretation: ≥5 mm positive if HIV, recent contact, immunosuppressed, fibrotic CXR; ≥10 mm if high-risk demographic; ≥15 mm for low-risk patients.
  • IGRA preferred over TST in BCG-vaccinated individuals (BCG can cause false-positive TST).
  • Rifampin turns body fluids orange and is a potent CYP3A4 inducer — reduces efficacy of OCPs, warfarin, ART, statins, and many others.
  • Pregnancy: use RIPE without streptomycin (ototoxic to fetus); pyridoxine essential. Treat LTBI in pregnant women only if recent infection or HIV+; otherwise defer postpartum.

References

  • CDC/IDSA/NTCA 2020 — Guidelines for the Treatment of Latent Tuberculosis Infection (Sterling et al., MMWR 2020)
  • ATS/CDC/IDSA 2016 — Treatment of Drug-Susceptible Tuberculosis (Nahid et al., Clin Infect Dis 2016)
  • WHO 2022 — WHO Consolidated Guidelines on Tuberculosis: Drug-Resistant TB Treatment (2022 Update)
  • Nix-TB / ZeNix Trials — Bedaquiline-Pretomanid-Linezolid for Highly Drug-Resistant TB (Conradie et al., NEJM 2020/2022)

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Commonly confused with

vs Sarcoidosis

Related Pulmonary diagnoses

AsthmaChronic Obstructive Pulmonary Disease (COPD)Community-Acquired Pneumonia (CAP)Hospital-Acquired and Ventilator-Associated Pneumonia (HAP/VAP)Aspiration Pneumonia and PneumonitisPulmonary Embolism (PE)Pulmonary HypertensionPneumothorax (Spontaneous and Tension)Pleural EffusionAcute Respiratory Distress Syndrome (ARDS)Lung Cancer (Small Cell and Non-Small Cell)BronchiectasisCystic FibrosisSarcoidosis

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