A prospective study of the risk of tuberculosis among HIV-infected patients

Abstract

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.