Indicator Profile of Influenza Virus Infections

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, except in very young children. It is estimated that 30 to 60 million U.S. residents get influenza each year. About 100,000 of them are hospitalized and an estimated 36,000 die each year from complications associated with the disease.

Scientists classify influenza viruses 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. In a typical seasonal epidemic, Type A causes the majority of hospitalizations due to its severity. 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 then, without washing your hands, touch your eyes, nose, or mouth, 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. Populations exist that are particularly susceptible to severe complications of influenza. These populations include the elderly (greater then or equal to 65 years old), children less than 24 months old, those with chronic respiratory and cardiovascular disease, and those with chronic metabolic disease such as diabetes. Each year it is estimated that at least 1,000 influenza-associated hospitalizations occur, a portion of which die from the illness.

Data Notes

Please visit the following website to find current influenza data: http://health.utah.gov/epi/diseases/flu

Data Sources

Utah Department of Health, Bureau of Epidemiology; 

Definition

Since influenza surveillance is comprised of 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: Direct Fluorescence Antibody (DFA), rapid influenza tests, serological tests, and/or viral culture.

How We Calculated the Rates

Numerator: The 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, or student absences, depending on the surveillance component presented.
Denominator: The denominator associated with describing influenza activity depends on the surveillance component being presented. Please see the website at http://health.utah.gov/epi/diseases/flu/ for more information.

Page Content Updated On 06/11/08, Published on 06/13/08
Communicable Disease Epidemiology Program, Office of Epidemiology, Division of Epidemiology and Laboratory Services, Utah Department of Health, Salt Lake City, UT 84114-2104, Telephone: 801-538-6191, Fax: 801-538-9923, Website: health.utah.gov/els/epidemiology/comdisease.html, Contact: Melissa Stevens, Email: melissastevens@utah.gov
The information provided above is from the Utah Department of Health's Center for Health Data IBIS-PH web site (http://ibis.health.utah.gov). The information published on this website may be reproduced without permission. Please use the following citation: "Retrieved Thu, 21 August 2008 19:32:28 from Utah Department of Health, Center for Health Data, Indicator-Based Information System for Public Health Web site: http://ibis.health.utah.gov".

Content updated: Fri, 13 Jun 2008 11:07:10 MDT