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Objective: To evaluate the risk of developing active tuberculosis (TB) in a cohort of HIV-1 -infected patients.

Methods: Prospective longitudinal follow-up of 839 HIV-infected patients, of whom 505 (60%) were parenteral drug users and 269 (32%) homosexual men. Tuberculin skin tests were performed at baseline and annually thereafter. Prophylaxis with isoniazid (300 mg daily for 9 months) was offered to those with a positive tuberculin test (induration >=5mm). Diagnosis of TB was accepted if it could be confirmed microbiologically (acid-fast bacilli seen in Ziehl-Neelsen stains or grown in Lowenstein-Jensen cultures) or pathologically (presence of caseating granulomas) and patients had consistent clinical manifestations.

Results: Active TB developed in 23 out of the 733 (3.1%) patients with a negative tuberculin skin test after a mean follow-up of 16 $pM 11 months (range, 2-52 months), with an estimated cumulative probability of 1.5 and 7% after 1 and 3 years, respectively (or 2.4 per 100 patient-years). None of the 87 patients with a negative tuberculin test but a positive Multitest developed TB. Conversely, 106 patients had a positive tuberculin skin test (97 at baseline and nine who converted during follow-up). Active TB developed in seven out of the 26 not receiving prophylaxis or in whom prophylaxis had to be discontinued (16.2 per 100 patient-years), in four out of 61 patients 3-27 months after having completed 9 months of prophylaxis with isoniazid (8.9 per 100 patient-years) and in none of the 19 still receiving isoniazid. When TB was diagnosed, the mean CD4 lymphocyte count of the 34 patients who developed it during follow-up was 77 $pM 103 $$ 106/I (range/ -1-400 $$ 106/l).

Conclusions: Among HIV-infected patients in whom the tuberculin skin test is negative, the risk of developing active TB is sufficient to consider prophylaxis if the CD4 count falls below 400 $$ 106/l, at least in those patients with skin anergy living in high-risk geographical areas such as Spain. When the tuberculin skin test was positive, isoniazid (9 months) provided a 45% protection beyond the period of its administration.

(C) Lippincott-Raven Publishers.