Refining the definition of miliary/disseminated tuberculosis in Canada

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

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.

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.

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