Important Facts for Influenza Virus Infections
DefinitionSince influenza surveillance comprises several components, multiple definitions are used when describing influenza activity, including the following: number of visits for influenza-like illness (ILI) at sentinel sites, laboratory-confirmed cases, influenza-associated hospitalizations, and student absences from sentinel schools. Confirmation of an influenza case relies on laboratory testing using one of the following tests: Realtime PCR (RT-PCR), Direct Fluorescence Antibody (DFA), rapid influenza tests, serological tests, and/or viral culture. For seasonal influenza data collected by the Utah Department of Health, please visit [http://www.health.utah.gov/epi/diseases/influenza/surveillance/index.html]. Reports available include weekly updates and annual seasonal summaries.
NumeratorThe numerator associated with describing influenza activity depends on each surveillance component. Therefore, numerator data may include the number of ILI visits, laboratory-confirmed cases, influenza-associated hospitalizations, pneumonia and influenza deaths, or student absences, depending on the surveillance component presented. For seasonal influenza data collected by the Utah Department of Health, please visit [http://www.health.utah.gov/epi/diseases/influenza/surveillance/index.html].
DenominatorThe denominator associated with describing influenza activity depends on the surveillance component being presented.
Why Is This Important?Influenza (flu) is a very contagious viral infection of the nose, throat, bronchial tubes, and lungs. Influenza is a respiratory infection and does not typically involve gastrointestinal symptoms. In some very young children the infection can cause gastrointestinal symptoms. It is estimated that nearly 16 million to 63 million U.S. residents get influenza each year and about 200,000 of them are hospitalized. The estimated annual death toll from complications associated with the disease ranges from 3,000 to 49,000. Influenza viruses are classified into types A, B, and C. Influenza type A and B viruses typically cause the most serious illnesses. Type A viruses are usually the cause of the most serious epidemics, and the most severe illness (influenza-associated hospitalizations). Type B viruses can cause epidemics, but illness is usually milder than illnesses caused by type A viruses. Type C is less common and typically only causes mild illness in humans. Each type of influenza includes many different strains which tend to change each year. Due to the fact that the strains can change each year, people do not build resistance, or immunity, to the next upcoming influenza strain. Every year, 9 to 10 months before the next influenza ("flu") season, scientists begin to prepare a new vaccine. Influenza vaccines include inactivated or killed virus from both A and B strains. People who have influenza can make you sick if they cough or sneeze near you. The viruses can pass through the air and enter your body through your nose or mouth. Influenza can also be spread if you touch things like a telephone or doorknob that has been contaminated by someone who has influenza. If you touch a contaminated surface and touch your eyes, nose, or mouth without washing your hands, you can become sick. Most people recover from influenza within one week, however, some have life-threatening complications, such as pneumonia, and may need to be hospitalized. In fact, most influenza-related deaths are due to pneumonia. There are certain populations that are at risk for severe complications of influenza. These populations include the elderly (65 years of age and older), children less than 24 months old, those with chronic respiratory and cardiovascular disease, and those with chronic metabolic disease such as diabetes. During the 2014-2015 influenza season, approximately 1,400 Utah residents were hospitalized due to influenza-associated hospitalizations. Nearly 1 in 12 Utah resident deaths (7.8%) had pneumonia and/or influenza listed as the cause of death. The 2009 H1N1 pandemic caused a lot of sickness in Utah. From June of 2009 until September 2010, over 1,300 hospitalizations and 45 deaths due to H1N1 were reported in Utah. The H1N1 strain of the influenza virus affected the population differently than what is seen during a typical influenza season. Generally during an influenza season it is the very young and very old most affected, but with 2009 H1N1 influenza two-thirds, or roughly 67%, of all cases were in individuals aged 5 to 64 years. Within the most recent influenza season (2014-2015) a majority of cases occurred during the months of December through February with most cases testing positive for a mutated, or "drifted", strain of influenza A, H3 virus that was not included in the season's vaccine. In many cases, the body's immune system may not recognize these newer strains because they have "drifted" in disease causing properties from the old strains. Influenza B persisted through the end of the 2014-2015 season.
Healthy People Objective IID-22:Increase the number of public health laboratories monitoring influenza virus resistance to antiviral agents
U.S. Target: 25 public health laboratories