[Adherence and effectiveness of the treatment of latent tuberculosis infection with isoniazid for 9 months in a cohort of 755 patients].

Background And Objective: The effectiveness of the treatment of latent tuberculosis infection depends on its efficacy, the adherence to treatment and patient's risk of tuberculosis. The objective of this study was to evaluate the adherence to treatment with daily isoniazid for 9 months, its effectiviness and equivalent adherence with daily isoniazid for 6 months so that treatment can be as effective as with daily isoniazid for 9 months.

Patients And Method: Cohort of 755 contacts of patients with lung confirmed tuberculosis with latent tuberculosis infection treated from 1986 to 2004, classified according to risk of tuberculosis disease into converters (high risk), frequent and non-frequent contacts. Adherence's rate for daily isoniazid for 9 months is evaluated according to percentage of treatment completion and effectiveness achieved is the number necessary to treat for preventing one tuberculosis case. Efficacy (reduction of morbidity) with isoniazid for 9 months: 93%, and with isoniazid for 6 months: 69%.

Results: Adherence's rate: 53/59 (89.9%; 95% confidence interval [CI], 82.1-97.5%) in converters; 305/380 (80.3%; 95% CI, 76.3-84.3%) in frequent contacts; and 205/211 (64.9%; 95% CI, 59.6-70.2%) in non-frequent contacts. The number necessary to treat with isoniazid for 9 months was 9 for converters, 16 for frequent contacts, and 79 for non-frequent contacts. Equivalent adherence for daily isoniazid for 6 months was 121% for converters, 108% for frequent contacts and 87.5% for non-frequent contacts.

Conclusions: For latent tuberculosis infection, a 9-month-isoniazid treatment has the highest effectiveness in the converters and frequent contacts. Such high effectiveness is impossible to achieve with a daily 6-month-isoniazid regimen.