Continuing Education generally more pathogenic than influenza B. These viruses infect humans and a variety of animals; some of these strains may spread from animal species to humans as well. The influenza viruses are ever changing via antigenic drift and shift. Antigenic drift is a process by which the virus produces ongoing gene mutations resulting in new subtypes and altered virulence. Antigenic shift is less common, but creates virulent strains that are transmissible to a greater population of susceptible individuals which can cause a pandemic. The gene segments between two strains are re-assorted, presumably during a co-infection in a single host. The “Spanish flu” of 1918 was a result of an antigenic shift. This pandemic alone affected 20 to 50 million people globally and was responsible for 549,000 deaths in the U.S. The 2009 H1N1 influenza (also referred to as Swine Flu) pandemic was a recombinant influenza consisting of a mix of swine (pig), avian (bird), and human gene segments. Influenza Diagnosis. Respiratory illnesses caused by influenza virus infection are difficult to differentiate from other illnesses caused by respiratory pathogens based on signs and symptoms alone. Once the presence of influenza virus is confirmed in a region or community, healthy adults with acute influenza-like symptoms most likely have the infection. The accuracy of diagnosis in an influenza outbreak can be as high as 80 to 90 percent. Rapid diagnosis can also be made by testing respiratory secretions from nasopharyngeal samples and/or throat swabs. There are a variety of rapid tests with results available as quickly as 30 minutes. While some are useful in differentiating influenza A and influenza B, none of the current tests can distinguish between influenza A (H1N1) and influenza A (H3N2). The optimal use of rapid diagnostic tests in patient management is not yet defined. Transmission. Influenza viruses are spread primarily
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through large-particle respiratory droplet transmission via coughing or sneezing. Transmission requires close contact with a susceptible individual, since the large droplets do not remain suspended in the air and only travel a short distance. Transmission may also occur via contact with surfaces contaminated with respiratory droplets or through small particles suspended in the air. Influenza Vaccine. Each year in the U.S., a vaccine containing the antigens from the strains most likely to cause infection during the season is produced. At the time of writing this lesson, the vaccine contains three strains, two influenza A strains and one influenza B. The 20122013 vaccine contains the following: A/California/7/2009(H1N1) pdm09-like virus, A/Victoria/361/ 2011(H3N2)-like virus, and B/ Wisconsin/1/2010-like virus. The Centers for Disease Control and Prevention (CDC) recommends that everyone six months of age and older get a flu vaccine each year as soon as it is available. It is especially important for people who are at high risk of developing serious complications such as pneumonia. This includes individuals who have asthma, diabetes, chronic lung disease, are pregnant, or are 65 years of age and older. The vaccine is also important for those who live with, or care for, persons at high risk for developing serious complications. It takes about two weeks for antibodies to develop and provide protection against influenza. Despite the fact that immunity declines over time, most healthy adults and older children will remain protected throughout the season. There are two types of influenza vaccine: inactivated vaccine given by injection and live, attenuated influenza vaccine (LAIV) sprayed into the nostrils. The inactivated vaccine, referred to as the “flu shot,” may or may not contain thimerosal. The flu shot can be given to all persons aged six months and older.
A high-dose inactivated vaccine is also available for persons 65 years of age and older. This product has four times the amount of antigen in the standard formulation, and has been shown to provide higher antibody responses in older adults when compared to the standard dose. Side effects are minor and include soreness, redness, or swelling at the injection site; hoarseness; sore, red, or itchy eyes; cough; fever, aches, headache, itching, and fatigue. Life threatening severe reactions to either vaccine formulation are very rare. LAIV is recommended for healthy persons two through 49 years of age who are not pregnant and do not have chronic health conditions (heart disease, lung disease, asthma, kidney or liver disease, diabetes, anemia, or other blood disorders). The vaccine should not be given if a severe allergy to a component of the vaccine exists or if the patient has an allergy to eggs. It does not contain thimerosal or other preservatives. LAIV is made from a weakened virus and does not cause influenza, but may cause mild symptoms such as runny nose, cough, congestion, fever, headache, muscle aches, cough, chills, tiredness/weakness, sore throat, wheezing, abdominal pain, vomiting, or diarrhea. Specific product labeling and CDC vaccine information statements (http://www.cdc.gov/vaccines/pubs/vis/) should be referred to for complete prescribing instructions and recommendations. Antiviral Treatment/Prophylaxis. Influenza antiviral treatment can shorten the duration of fever, lessen symptoms, reduce the risk of complications from influenza, and shorten hospitalization stays. It is recommended to begin antiviral treatment as soon as possible ― ideally within 48 hours of illness onset, for any patient (1) with confirmed or suspected influenza who is hospitalized; (2) who has severe, complicated, or progressive illness; or (3) at higher risk of complications. Treatment should
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