Incidence of influenza in Ontario following the Universal Influenza Immunization Campaign
Section snippets
Background
In Canada, influenza and pneumonia (as a complication of influenza) are responsible for approximately 75,000 hospitalizations each year [1] and 700–2500 deaths [2], [3]. With roughly 40% of the population of Canada residing in Ontario, it could be extrapolated that in Ontario approximately 30,000 people are hospitalized annually due to influenza and pneumonia resulting in 280–1000 deaths. Previous research has examined causes of emergency department (ED) overcrowding [4], [5], [6], [7], and the
Objective
The objective of this study was to compare the incidence of influenza in Ontario before and after the implementation of the UIIC to determine if there has been a decrease in influenza following the UIIC.
Study design
This is a population-based, retrospective study of laboratory-confirmed influenza cases as reported to Health Canada from 1 January 1990 to 31 August 2005.
Influenza data collection
Influenza is a reportable disease in Ontario and the reporting definition is the presence of the following three symptoms:
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Fever greater than 39 °C.
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Cough or sore throat.
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Myalgia, malaise and/or prostration.
In addition, to at least one of the following:
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A laboratory confirmation by detection or isolation of influenza virus in pharyngeal or nasal
Descriptive statistics
All analyses, with the exception of the time series analysis, were performed using SPSS version 12 [15]. Monthly influenza counts were changed to rate per 100,000 population using annual Ontario population estimates from Statistics Canada [16]. The percent of influenza found in Ontario, with respect to the rest of Canada was compared using Mann–Whitney U-test for the years 1996–2005 (years for which Flu Watch data for the country as a whole were available).
It is possible that the rate of
Time series analysis
Multitaper time series analysis [17], [18] was used to compare the mean rate of influenza in Ontario prior to and following the introduction of the UIIC. As a preliminary check on the temporal structure of this data, the power spectrum was calculated using multitaper methods, supplemented by the harmonic F-test for periodic components. Multitaper analysis gives greater control over the resolution-bias-variance trade-off, and spectra thus obtained can be used to estimate the underlying system
Results
Fig. 1 shows laboratory-confirmed influenza cases in Ontario per 100,000 population from 1 January 1990 to 31 August 2005.
Table 1 shows the number of influenza cases in Ontario as a percent of the total number of cases in Canada before and after the introduction of the UIIC in 1999/2000. There is not a significant difference in the percent of influenza cases following the introduction of the UIIC (p = 1.00).
The ratio of the rate of influenza in Ontario, with respect to other regions in Canada is
Comment
The Universal Immunization Campaign was introduced in Ontario in July 2000 with two primary objectives: to reduce ED pressure in the winter and to reduce the incidence of influenza [11]. The present study was unable to find a significant reduction in the incidence of influenza in Ontario following the introduction of the UIIC. The ratio of influenza rates in Ontario to other regions of Canada and the number of tests performed was also examined and, in the majority of cases, there was no
Conclusion
The findings of this study do not show a reduction in the rate of influenza in Ontario following the introduction of the Universal Influenza Immunization Campaign. Given that the individuals at low risk for complications from influenza are less likely to seek medical attention and less likely to develop complications, it may be more cost effective to target high risk individuals [34]. In their 1993 paper, Duclos and Hatcher state: “from our findings, the most effective approach to increase the
Limitations
Any assessment of the Universal Immunization Campaign will be affected by the lack of data on vaccine coverage in Ontario. No uniform baseline data on pre-UIIC vaccine coverage were collected, thus it is impossible to know how many low risk individuals received the influenza vaccination, or what their health outcomes were. Data on vaccine coverage is still not systematically collected, and although individual Health Units and physician offices may keep their own records regarding vaccinations
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