Tuberculosis

Etiology and epidemiology

Tuberculosis is particularly common (up to 5C per cent) in HIV-infected patients from countries with a high prevalence of Mycobacterium tuberculosis, in intravenous drug users, and in localized areas of countries with an otherwise low prevalence (e.g. New York City). Even in low-prevalence countries such as the United Kingdom 5

per cent or more of HIV-infected patients will develop tuberculosis.

Clinical features

At CD4 counts over 300 * 106/l the presentation is similar to that in the immunocompetent, with lung and lymph node disease predominating and the pulmonary disease largely focal. Typical symptoms include fever, weight loss, and cough. As the CD4 count falls the clinical disease becomes less typical; extrapulmonary disease is present in two-thirds of patients, and pulmonary involvement is more widespread and rapidly progressive, often simulating acute bacterial infection and P. carinii pneumonitis.

Investigations

At high CD4 counts the chest radiograph will show focal, often apical, consolidation with cavitation or pleural effusion. Hilar and mediastinal lymphadenopathy are seen in 30 per cent of patients. At lower CD4 counts the chest radiograph is often indistinguishable from that with other respiratory diseases such as acute bacterial infection and P. carinii pneumonitis. The chest radiograph is normal in up to 20 per cent of patients with pulmonary involvement. Only 60 per cent of those with pulmonary disease will be sputum smear positive for acid-fast bacilli, although microscopy of bronchoscopic alveolar lavage fluid will increase the sensitivity to 80 to 90 per cent, with the remainder being identified on culture.

Treatment

All patients with confirmed or suspected tuberculosis should be isolated. The normal initial therapy is rifampin (rifampicin) 450 to 600 mg/day, isoniazid 300 mg/day, and pyrazinamide 1.5 to 2 g/day, with the addition of ethambutol 15 mg/kg/day if there is a significant (over 2 per cent) risk of resistance to isoniazid. After 2 months of therapy ethambutol and pyrazinamide are stopped, but the other drugs are continued for 6 months. Outbreaks of infection due to multidrug-resistant organisms have been reported. In these cases treatment should be guided by local susceptibility patterns and the results of antibiotic sensitivity testing of the organism.

Critical care

Management is the same as for P. carinii pneumonitis. It is important to isolate such patients. Other respiratory infections

Infection with fungi such as Cryptococcus species, Aspergillus species, and Histoplasma capsulatum, atypical mycobacteria such as the M. avium complex and Mycobacterium kansasii, and other organisms such as Nocardia asteroides and cytomegalovirus are uncommon causes of acute respiratory failure and are normally encountered in patients with low CD4 counts (below 150 * 106/l).

Pulmonary malignancy

The two most common malignancies associated with HIV are Kaposi's sarcoma and non-Hodgkin's lymphoma. Hodgkin's lymphoma is also seen with increased frequency. Pulmonary Kaposi's sarcoma is normally only seen in patients with low CD4 counts (below 200 * 10 6/l) who have cutaneous and palatal lesions, and it can cause extensive lung disease. Non-Hodgkin's lymphoma and Hodgkin's lymphoma may be seen at any stage of HIV and behave more aggressively at lower CD4 counts; they only rarely involve the lung.

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