Clinical outcomes of pyrazinamide-monoresistant Mycobacterium tuberculosis in Quebec

In Quebec, 6.2% of all tuberculosis (TB) isolates from Canadian-born patients are resistant to pyrazinamide (PZA) alone. The clinical significance of PZA-monoresistant (PZA(MR)) TB is unknown.

Canadian-born patients with PZA(MR) TB diagnosed between 1 January 1990 and 31 December 2000 and reported in a prior study were compared to randomly selected Canadian-born patients with fully susceptible isolates diagnosed within the same time period.

A total of 318 patients were eligible, of whom 40 (12.6%) had missing outcome information. Mean total duration of treatment was respectively 9.0 and 8.9 months for those with PZA(MR) and pan-susceptible strains. Respectively 91% and 89% of PZA(MR) and pan-susceptible patients received at least 6 months of rifampin-containing treatment. Among 67 patients with PZA(MR) TB, 51 (76%) were cured, 3 (4%) relapsed, none failed treatment, and 16 (24%) died within 6 months of diagnosis. Of 211 subjects with fully susceptible isolates, 181 (86%) were cured, 2 (1%) relapsed, 2 (1%) failed treatment, and 30 (14%) died within 6 months of diagnosis. PZA monoresistance was associated with decreased odds of successful clinical outcomes compared with pan-susceptible TB (OR 0.4, 95%CI 0.2-0.8).

Patients with PZA(MR) TB had significantly worse clinical outcomes than patients with fully susceptible strains.