The first wave of the 1918 influenza pandemic among soldiers of the Canadian expeditionary force.

OBJECTIVES: This article evaluates the evidence for the presence of the first, mild wave of the 1918 influenza pandemic among soldiers in the Canadian Expeditionary Force (CEF). METHODS: Death records for soldiers in the CEF who died in Canada in 1917 and 1918 were extracted from the Commonwealth War Graves Commission and record-linked to the Canada War Graves Registers, Circumstances of Casualty database. Monthly mortality rates from pneumonia and influenza (P&I) were compared with mortality rates from all other causes for 1917 and 1918, and by region for 1918. RESULTS: The herald wave of influenza was present among CEF soldiers in 1918. P&I mortality was significantly higher in March and April 1918 than during the same period in 1917. P&I mortality rates varied across the country and were significantly higher among soldiers who died in the Maritime region of Canada. In March, Maritime P&I mortality was significantly higher than its counterpart in the West; in April it was significantly higher than P&I mortality in both the Central and Western regions. CONCLUSIONS: The CEF findings suggest that local, geographic heterogeneity characterized the first wave of the 1918 influenza pandemic in Canada and illustrate the ways in which well-established, historical patterns of cross-border social contact with the United States, coupled with the special conditions created by warfare, disproportionately funnelled influenza into particular regions. Identification of the mild first wave among soldiers in the CEF calls for more research on the civilian experience of both waves of influenza in Canada.