REFINING THE DEFINITION OF MILIARY/DISSEMINATED TUBERCULOSIS IN CANADA.

ABSTRACT

OBJECTIVE: While a multi-site 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 TB patients in Canada. Definitions were combined in a multi-variable logistic regression to determine risk factors for TB-related death in DTB. RESULTS: We applied two mutually exclusive definitions of DTB to our dataset 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 TB patients, 110 (3.8%) met the 'strict' definition, while 168 (5.8%) met the 'multisite' definition. Of all 278 DTB patients 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. DTB patients, by either definition, were less likely to achieve cure/treatment completion and more likely to die. 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 both a strict and multisite definition of DTB for purposes of reporting consistency and investigational comparability.