HIV & TB

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First posted December 2006 by Charles Gomersall

Epidemiology

• significant proportion of patients with TB in Western countries are infected with HIV
• TB is the cause of death in ~10% of patients with HIV
• disease may be due to primary disease or reactivation

Clinical features

• depend on degree of immunosuppression
  • CD4⁺>350 cells/µl
    • clinical presentation similar to TB in non HIV-infected patients although extra-pulmonary disease more common
  • CD4⁺<350 cells/µl
    • extrapulmonary disease (pleuritis, pericarditis, meningitis) common
  • severely immunocompromised
    • may present as severe systemic disease with high fevers, rapid progression and systemic sepsis
    • CXR findings of pulmonary TB differ from patients with less advanced HIV disease:
      • lower and middle lobe disease more common
      • miliary infiltrates common
      • cavitation less common
    • sputum smears and culture results may be positive even with a normal CXR

Investigations

• sputum smear and culture less sensitive in severely immunocompromised patients and tuberculin skin test often negative in these patients
• yield of mycobacterial stain and culture of specimens from extra-pulmonary sites higher in these patients
• mycobacterial blood culture may be positive in patients with disseminated disease
  • more sensitive in patients with severe immunodeficiency
• positive smear indicates mycobacterial disease but not necessarily TB. However, as TB is the the most virulent mycobacterial disease, anti-TB treatment should be started until definitive identification can be made

Treatment

Should include at least:

• 6 months isoniazid and rifampicin or rifabutin
• 2 months of pyrazinamide and ethambutol
  • ethambutol can be discontinued if organism is known to be sensitive to other three drugs

Other regimes are recommended for patients with serum aminotransferase concentrations >3 times upper limit of normal before the start of therapy and for management of drug resistance or treatment failure.

In addition to the usual complications of anti-TB therapy, patients with HIV disease are at risk of developing an immune reconstitution reaction, particularly those who are concurrently receiving anti-retroviral therapy.

Anti-retroviral therapy

Substantial adverse drug interactions occur between rifamycins (eg rifampicin, rifabutin) and commonly used anti-retrovirals as a result of induction of the the hepatic cytochrome P450 system. Rifampicin is the most potent inducer with rifabutin resulting in significantly less induction.

Click here for IDSA recommended dose adjustments when anti-retroviral therapy and rifabutin are adminstered simultaneously.

The optimal time for initiating anti-retroviral therapy in patients with TB is controversial. Although early therapy may decrease HIV disease progression it may be associated with a relatively high incidence of adverse effects and immune reconstitution reactions. Most clinicians choose to wait 4-8 weeks. Patients already receiving anti-retroviral therapy at the time of diagnosis of TB require careful review of their therapy.

Further reading

Treating Opportunistic Infections among HIV-Infected Adults and Adolescents: Recommendations from CDC, the National Institutes of Health, and the HIV Medicine Association/Infectious Diseases Society of America

© Charles Gomersall, December 2006

©Charles Gomersall, October, 2009 unless otherwise stated. The author, editor and The Chinese University of Hong Kong take no responsibility for any adverse event resulting from the use of this webpage.
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