Can a universal influenza immunization program reduce emergency department volume?

In 2000 the Ontario Minister of Health and Long-Term Care announced a universal influenza immunization program for Ontario, Canada. The 2 objectives of this $38-million program were to decrease seasonal impact of influenza on emergency department (ED) visits and to decrease the number and severity of influenza cases. This paper examines the correlation between population influenza rates and ED visits in 5 tertiary care hospitals in Ontario over a 5-year period (1996-2001).

In this retrospective, observational study, we determined the total number of ED visits during the study period, by month, at 5 tertiary care hospitals in 3 Ontario cities Kingston, London and Ottawa). Detailed ED diagnoses were captured for Kingston, and provincial and national population-based influenza rates were obtained from Health Canada for the 5-year study period. Correlation and regression analyses were used to determine the relationship of influenza rates and ED volumes. "Influenza season" is defined in this study as November 1st to March 31st of each year.

There was no significant correlation between influenza rates and ED volumes, with Pearson correlation coefficients (r) of 0.22 (p = 0.72), 0.33 (p = 0.59) and 0.27 (p = 0.66) at the Kingston, London and Ottawa study sites, respectively. Data from the Kingston hospitals showed that, during influenza season, acute respiratory diagnoses accounted for only 4.4% of ED visits and influenza for only 0.34% of visits. Multiple linear regression analysis showed that the ED diagnosis of influenza was not significantly related to ED volume. During the influenza season after the universal immunization campaign, ED visits increased at all sites.

Based on this study, a universal influenza immunization campaign is unlikely to affect ED volume.