Michele Kohli, BSc, MSc
The persistence of influenza in the North American population has not been completely explained by epidemiologists.1 During the last influenza season (1997-98), there were 5,148 laboratory confirmed cases of influenza in Canada (see Table 1).2 The elderly population, those aged 65 years and above, are particularly susceptible to this disease. Over 95% of the deaths caused by influenza occur in this age group, in part, because of the higher prevalence of congestive heart failure and lung disease.1 Last year, the occurrence of influenza peaked between January and March.2 When the prevalence of influenza is high in a population, patients presenting with a febrile respiratory illness along with symptoms such as myalgia, headache, sore throat and cough are often diagnosed as having influenza.1 However, the gold standard for diagnosis is laboratory detection of the virus in nasopharyngeal swabs.1 The genes of the influenza virus mutate frequently, causing the antigenic molecules of the virus to change, resulting in the emergence of new viral sub-types. This process is known as antigenic drift. When human and swine or avian strains of influenza A recombine, the resulting new subtypes can cause pandemics.
