Tuberculosis in HIV

Key Features

Essentials of Diagnosis

• Fatigue, weight loss, fever, night sweats, and cough

• Pulmonary infiltrates on chest radiograph, including nodular or cavitating

• Positive tuberculin skin test reaction (most cases)

• Smear of sputum positive for acid-fast bacilli, rapid molecular testing positive, or culture of sputum positive for Mycobacterium tuberculosis (MTB)

General Considerations

• Latent tuberculosis infection (LTBI) occurs when bacilli are contained within granulomata, the typical response to infection in immunocompetent persons

  • Nontransmissible, but may become active disease if a person's immune function becomes impaired

  • Reactivation occurs within 2 years in up to 50% of HIV-positive patients

• Medication nonadherence is a major cause of treatment failure, disease transmission, and development of drug resistance

• Resistance may be to single or multiple drugs

  • Drug-resistant TB is resistant to one first-line antituberculous drug, either isoniazid or rifampin

  • Multidrug-resistant tuberculosis (MDR-TB) is resistant to isoniazid and rifampin, and possibly additional agents

  • Extensively drug-resistant tuberculosis (XDR-TB) is resistant to isoniazid, rifampin, fluoroquinolones and either aminoglycosides or capreomycin or both

Demographics

• HIV increases the risk of reactivation tuberculosis

• Risk factors for drug resistance include

  • Immigration from a region with drug-resistant tuberculosis

  • Close contact with a patient infected with drug-resistant tuberculosis

  • Unsuccessful prior therapy

  • Patient noncompliance

Clinical Findings

Symptoms and Signs

• Cough is most common

• Blood-streaked sputum is common; frank hemoptysis is rare

• Slowly progressive constitutional symptoms

  • Malaise

  • Anorexia

  • Weight loss

  • Fever

  • Night sweats

• Patients appear chronically ill and malnourished

• Chest examination is nonspecific; post-tussive apical rales are classic

• Extrapulmonary disease is especially common, often with lymphadenitis or miliary disease

• Atypical presentations are common

Differential Diagnosis

• Pneumonia or lung abscess

• Lung cancer

• Lymphoma

• Mycobacterium avium complex (or other nontuberculous mycobacteria)

• Sarcoidosis

• Fungal infection (eg, histoplasmosis)

• Endocarditis

• Nocardiosis

Diagnosis

Laboratory Tests

• Tuberculin skin test (TST)

  • The Mantoux test is the preferred method: 0.1 mL of purified protein derivative (PPD) containing 5 tuberculin units is injected intradermally on the volar surface of the forearm using a 27-gauge needle on a tuberculin syringe. After 48–72 hours, the transverse width in millimeters of induration at the skin test site is measured

  • Table 9–13 summarizes the criteria established by the Centers for Disease Control and Prevention (CDC) for interpretation of the Mantoux TST

• Interferon gamma release assays (IGRAs) (including the QuantiFERON and T-SPOT tests) are in vitro assays of CD4+ T-cell-mediated interferon gamma release in response to stimulation by specific M tuberculosis antigens

  • In endemic areas, IGRAs are no more sensitive than the TST in active tuberculosis (20–40% false-negative rate) and cannot distinguish active from latent disease

  • IGRAs should not be used to exclude active tuberculosis