Introduction

Tuberculosis is not more infective in the HIV-positive patient than in other individuals.  HIV-positive patients acquire TB at rates similar to those of the general population.  The difference is that the HIV-positive patient has less natural immunity, and so the consequences of TB infection are potentially more serious.  Once active disease has occurred, it may also progress more rapidly in HIV-positive patients. 

Aetiology of tuberculosis in HIV-positive patients

The major pathogen responsible for tuberculosis is Mycobacterium tuberculosis, although species including Mycobacterium kansaii, Mycobacterium marinum, Mycobacterium avium, Mycobacterium intracellulare and Mycobacterium fortuitum have been reported to cause tuberculosis.  These atypical species are usually more resistant to antituberculosis drugs compared to Mycobacterium tuberculosis.  This is a particular concern as Mycobacterium avium is becoming more prominent in HIV-positive patients.  Emergence of drug-resistant forms of Mycobacterium tuberculosis also requires consideration during therapy.

Diagnosis of TB in the HIV-positive patient

Presentation is often atypical and a high index of suspicion is required for diagnosis.  TB in HIV-positive patients is likely to:

• Present atypically with:
  • Negative sputum smears
  • Lack of tuberculin skin reaction with low CD4+ counts
  • Pleural or pericardial disease and disseminated disease
  • Bilateral, unilateral or lower zone shadowing.
• Reappear after a period of dormancy
  • Progression to active disease is 5–10% per year (50% lifetime risk) in patients with HIV, compared to a 10% lifetime risk in the general population.
• Progress more rapidly
• Possibly be drug-resistant. 

Active pulmonary TB occurs when CD4+ counts are still relatively high (250–500/ml).  As CD4+ cell counts fall, disseminated TB becomes more likely.

Management of TB in the HIV-positive patient

The treatment should be supervised by a physician with full training in the management of TB with direct access to a TB nurse or health visitor especially if MDR-TB is suspected or confirmed. Seek specialist advice.

Decisions on the type of isolation required should be made at consultant level, in discussion with the Infection Control Doctor, considering the infectiousness of the patient, the type of facilities available, local policies and the possibility of multi-drug resistant strains of TB.

• Previous BCG vaccine may not provide the expected immunity and new vaccination is not recommended, as the vaccine is live.
• Isoniazid resistance is higher in HIV-positive patients co-infected with TB in the UK.
• Drug resistance may occur because the bacterial load is higher, but it usually results from inappropriate therapy and poor patient compliance.  The infecting pathogen may be one of many resistant forms, including:
• Isoniazid resistant — often seen in HIV-positive patients
• Pyrazinamide resistant — rare in Mycobacterium tuberculosis although Mycobacterium bovis is naturally resistant
• Dual streptomycin/isoniazid resistant — commonest dual resistance and managed as for isoniazid resistance
• Multi-drug resistant — isoniazid and rifampicin resistant, with or without resistance to another antituberculosis drug, disease requires complex therapy involving 5–6 drugs for up to 24 months depending on HIV status and resistance profile.
• A TB-infected patient on an HIV ward is a serious threat to the surrounding immunocompromised patients and isolation may be required.

Antimicrobial rationale

• HIV regimens and TB drugs may interact.
• The standard short-course 4-drug regimen is as effective for HIV-positive patients as for immunocompetent patients.  Treatment regimens have been recommended by the British Thoracic Society.
• Some side-effects may be caused by the TB treatment eg. hepatitis, liver damage and peripheral neuropathy.
• Relapses are common if antimicrobial therapy is not adhered to.  Patient compliance can be increased and the possibility of relapse reduced by administering TB drugs via directly observed therapy (DOT) clinics.

Following treatment for tuberculosis, chemoprophylaxis is not recommended due to the possible emergence of drug-resistance.  However, due to the lifelong risk of recurrence, the patient should undergo follow-up with a tuberculosis specialist as well as their HIV specialist.

Department of Health guidelines on the prevention and control of tuberculosis in the United Kingdom.

Principles of prophylaxis

Chemoprophylaxis is not always appropriate due to incidence of drug-resistant pathogens, however:

• A 3–6 month treatment programme with 1 or 2 drugs is recommended if patient has been exposed to significant risk of tuberculosis infection
• A 6 month treatment programme with 2 or 3 drugs is recommended if patient has been in close contact with multi-drug resistant tuberculosis (MDR-TB).

Department of Health guidelines on the prevention and control of tuberculosis in the United Kingdom.