Winter means influenza season and as such should be a reminder that prevention is always better than treatment.

Influenza kills approximately 36,000 people worldwide on a yearly basis and 90 % of those people are 65 and older.

It is thought that influenza affects 20 % of children and 5 % of adults yearly. It is transmitted like most viruses by inhalation of aerosolized secretions from infected people. These secretions are aerosolized by talking, sneezing, or coughing.

Generally two types are known to cause community outbreaks and even epidemics, influenza A and B. There is an influenza C but it causes very mild disease.

The virus changes significantly enough from year to year that there is no immunity from previous vaccination.

Pandemics are luckily rare and have occurred 4 times since 1918. The one with which you are likely most familiar occurred in 2009. This was caused by an influenza type A virus (H1N1) or ‘swine flu.? This usually occurs when there is a novel gene rearrangement in the virus. The milder year-to-year changes that require new seasonal vaccines are considered antigenic shifts.

Epidemics usually occur from late fall to early spring. ?The CDC publishes weekly updates on influenza outbreaks during flu season.

Like most viruses the real complications occur with secondary infections. Influenza generally causes fever and muscle aches. If a productive cough and shortness of breath develop concern for pneumonia is heightened. This secondary bacterial pneumonia accounts for 25 % of deaths from influenza.

People who are over 65 have a higher rate of complication from the flu. People with medical conditions that include chronic pulmonary disease or cardiovascular conditions also experience more complications than healthy counterparts. Other chronic conditions that may leave a patient vulnerable to serious sickness from influenza include kidney disease and diabetes. It is imperative that people in these categories receive vaccination to prevent influenza because of the possible devastating effects of a complicated course of illness with influenza.

Children are also at higher risk of complication from influenza and therefore it is important that people who care for infants aged 6 to 59 months are immunized so as to not spread the infection to this vulnerable population.

Other at risk groups include pregnant women, people undergoing chemotherapy or immunosuppression, and residents of chronic care facilities.

Symptoms are very general and include an upper respiratory infection with fever and possible muscle aches. Generally sore throat and swollen glands are not necessarily typical of flu and may be a result of another type of viral or bacterial illness. Cough and shortness of breath that develops several days after the onset of cold symptoms with fever may be signs of a secondary bacterial infection.

Treatment is generally supportive (rest and fluids). There are antiviral medications which may shorten the course of the illness by 1-2 days if instituted quickly (within 2 days of symptom onset). These medications do not help symptoms caused by non influenza viruses. The typical use of these medications are for high risk individuals who live in households with someone who was positively diagnosed with influenza. Use of these medications helps reduce the transmission of influenza in households.

The most important take home message regarding influenza is that prevention is key and vaccination can help save lives.