Influenza is a respiratory infection caused by the influenza virus. It is rife in North America, especially from December to April, and can cause major epidemics. It is spread through secretions from the nose or throat, when coughing or sneezing, or through contaminated hands or objects. It usually presents with a sudden fever, chills, headache, body aches, dry cough, sore throat, and severe general malaise that lasts for several days. In children, influenza is more often accompanied by nausea, vomiting and diarrhea. In the elderly, fever may be minimal, and influenza may present with general impairment, dizziness, confusion, or prostration. Influenza usually resolves spontaneously within 5 to 7 days, although cough and fatigue may persist for 2 weeks or more.
Influenza can lead to more serious consequences such as pneumonia, hospitalization and death. In Quebec, there are between 1,000 and 1,500 deaths each year linked to influenza and its complications. This is especially true in the elderly and in those with underlying chronic health conditions. Over 90% of deaths from pneumonia and influenza occur in people 65 years of age or older. Mortality from influenza in the elderly is 20 to 30 times higher in the presence of an underlying chronic disease. In addition, it has been found that children under 2 years of age are at as high a risk of being hospitalized with influenza as that of the elderly or those with chronic health problems. Pregnant women are also at higher risk of being hospitalized with influenza, especially during the 3rd trimester.
It is important to distinguish influenza from common respiratory infections, such as the common cold, which are harmless.
In 2011 and 2012, following the AH1N1 influenza epidemic, the influenza vaccine also protected against the AH1N1 influenza.