Tuberculosis prophylaxis in patients with steroid treatment and systemic rheumatic diseases. A case-control study

Objective The aim of this study was to assess the impact of isoniazid prophylaxis in patients with systemic rheumatic diseases who attended a teaching hospital in Mexico City between 1987 and 1992. Methods In this case-control study, patients with systemic rheumatic diseases and tuberculosis (cases) were compared with patients with systemic rheumatic diseases without tuberculosis (controls). The groups were matched by year of hospital admission and rheumatic disease. Clinical charts were reviewed for: 1) isoniazid prophylaxis, defined as the administration of isoniazid 300 mg/day for 6 or more months in patients with exposure to steroids (prophylaxis with isoniazid was defined as complete, incomplete or any prophylaxis); 2) exposure to steroids: defined as the administration of prednisone > 15 mg/day (or its equivalent of another steroid) for 3 or more months before tuberculosis or recruitment into the study; 3) exposure to immunosuppressants, defined as the administration of any dose of azathioprine, methotrexate, cyclophosphamide, and/or 6-mercaptopurine, before tuberculosis in the cases or recruitment date in the controls; 4) reactivity to PPD; and 5) other relevant variables. Results Twenty cases and 66 controls were studied. A 70% decrease in the risk of developing tuberculosis was found among patients who received any prophylaxis with isoniazid as compared to controls: OR 0.31, 95% Cl 0.09 -0.98, p = 0.03. A 97% decrease was seen in those patients who received complete prophylaxis: OR 0.034, 95% CI 0.0001 - 0.216, p 15 mg/day for three or more months) may be useful to prevent tuberculosis, independently of the results of the PPD reactivity test. However, a controlled clinical trial will be required to confirm these results.