Objective: Public health emergency planning includes a consideration of public health human resource requirements. We addressed the hypothetical question: How many public health physicians could Canada mobilize in the event of a public health emergency? Methods: We used the 2004 National Physician Survey (NPS) to estimate the number of public health physicians in Canada. Using weighting to account for non-response, we estimated the numbers and population estimates of public health physicians who were active versus 'in reserve'. We explored the impact of using diverse definitions of public health physician based upon NPS questions on professional activity, self-reported degrees and certifications, and physician database classifications. Results: Of all Canadian physicians, an estimated 769 (1.3%) are qualified to practice public health by virtue of degrees and certifications relevant to public health, of whom 367 (48%) also report active 'community medicine/public health' practice. Even among Canada's 382 Community Medicine specialists, only 60% report active public health practice. Conclusion: The estimation of the size of Canada's public health physician workforce is currently limited by the lack of a clear definition and appropriate monitoring. It appears that, even with a reserve public health physician workforce that would almost double its numbers, Canada's available workforce is only 40% of projected requirements. Public health emergency preparedness planning exercises should clearly delineate public health physician roles and needs, and action should be taken accordingly to enhance the numbers of Canadian public health physicians and their capacity to meet these requirements.
