Refining the definition of miliary/disseminated tuberculosis in Canada.

Objectives: Although a "multisite" definition of disseminated tuberculosis (DTB) exists, there is limited evidence to support its use. Herein, we sought to generate that evidence.

Methods: We evaluated treatment outcomes and reporting requirements against two distinct definitions of DTB in a 15-year population-based cohort of consecutively diagnosed patients with tuberculosis (TB) in Canada. Definitions were combined in a multi-variable logistic regression to determine the risk factors for TB-related death in DTB.

Results: We applied two mutually exclusive definitions of DTB to our data set: 1. "strict" - TB disease associated with a positive TB culture in blood/bone marrow or TB disease associated with a miliary pattern on chest imaging and a positive TB culture or, 2. multisite - TB disease in two or more non-contiguous sites. Among 2877 notified patients with TB, 110 (3.8%) met the strict definition, whereas 168 (5.8%) met the multisite definition. Of all 278 patients with DTB, only 135 (48.6%) were notified as DTB using International Classification of Disease codes and only 66 (23.7%) were classified as DTB by Canada's Public Health Agency. Patients with DTB by either definition were less likely to achieve cure/treatment completion and more likely to die. The risk factors for a fatal outcome included extremes of age, Canadian birth, central nervous system involvement, and HIV co-infection.

Conclusion: Our findings support the combination of a strict and multisite definition of DTB for purposes of reporting consistency and investigational comparability.