Isoniazid-monoresistant tuberculosis in the United States, 1993 to 2003

Seven percent of tuberculosis (TB) cases reported to the US National Tuberculosis Surveillance System in 2005 had Mycobacterium tuberculosis isolates with resistance to at least isoniazid.

We undertook this study to describe demographic characteristics, risk factor information, and treatment outcomes for persons with isoniazid-monoresistant (resistant to isoniazid and susceptible to rifampin, pyrazinamide, and ethambutol hydrochloride) TB compared with persons with TB susceptible to all first-line anti-TB drugs.

The numbers of isoniazid-monoresistant TB cases increased from 303 (4.1%) in 1993 to 351 (4.2%) in 2005. In our multivariate analysis of all TB cases reported from 1993 to 2003, the races/ethnicities of patients with isoniazid-monoresistant TB were significantly more likely to be US-born Asian/Pacific Islander (adjusted odds ratio [aOR], 1.9; 95% confidence interval [CI], 1.4-2.6), foreign-born Asian/Pacific Islander (1.8; 1.4-2.1), foreign-born black non-Hispanic (1.4; 1.1-1.7), or US-born Hispanic (1.3; 1.1-1.5). Isoniazid monoresistance was also associated with failure to complete therapy within 1 year (aOR, 1.7; 95% CI, 1.5-1.8), a history of TB (1.5; 1.3-1.7), and correctional facility residence (1.5; 1.2-1.7).

Isoniazid-monoresistant TB did not decline from January 1, 1993, through December 31, 2005, despite national downward trends observed in overall TB cases and in multidrug-resistant TB cases. Physicians must ensure completion of treatment for patients taking isoniazid as part of their TB or latent TB infection therapy. In addition, physicians should maintain heightened vigilance for isoniazid resistance when evaluating certain at-risk populations for TB and latent TB infection.