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Content on this page was developed during the 2009-2010 H1N1 pandemic and has not been updated.

  • The H1N1 virus that caused that pandemic is now a regular human flu virus and continues to circulate seasonally worldwide.
  • The English language content on this website is being archived for historic and reference purposes only.
  • For current, updated information on seasonal flu, including information about H1N1, see the CDC Seasonal Flu website.

Questions and Answers: Behavioral Risk Factor Surveillance System (BRFSS) 2009 H1N1 Flu Modules for Influenza-like Illness (ILI) and Vaccination

February 24, 2010 3:30 PM ET

The Behavioral Risk Factor Surveillance System (BRFSS) is a state-based system of health surveys that collects information on health risk behaviors, preventive health practices, and health care access primarily related to chronic disease and injury. 

To help track influenza activity during the 2009-2010 influenza season, modules (an optional set of questions that are asked along with the standard set of BRFSS questions) related to influenza-like illness (defined as an illness with reported fever and a cough and/or sore throat for this survey), and seasonal and 2009 H1N1 vaccines have been added to the survey.

For more information about BRFSS, see

What is BRFSS?

Established in 1984 by the Centers for Disease Control and Prevention (CDC), the Behavioral Risk Factor Surveillance System (BRFSS) is the world’s largest, on-going telephone health survey, interviewing more than 400,000 adults each year.  It tracks health conditions and risk behaviors monthly in all 50 states, the District of Columbia, Puerto Rico, the U.S. Virgin Islands, and Guam. 

Which states have included the influenza modules in their BRFSS survey?

The 2009 H1N1 influenza-like illness (ILI), and influenza vaccines modules for adults were accepted by 49 states the District of Columbia, Puerto Rico, the U.S. Virgin Islands, and Guam.  Fewer states and territories, 41, included the modules for children in their BRFSS surveys.

How is BRFSS data used?

The timely data on health related behaviors obtained by BRFSS is used by states to identify and track health objectives, and develop and evaluate public health policies and programs. 

How is the influenza BRFSS data about ILI being used this season?

The 2009 H1N1 ILI module is able to indicate how much ILI is reported in the participating states and territories.  In the data collected from September 1, 2009 – December 31, 2009 8.3% of the U.S. population reported having had ILI. 

When participants report that they have had ILI, they are asked follow-up questions, including whether they sought medical care for their illness.  Participants are also asked whether anyone in their households were hospitalized for ILI.  These data are supplemental to CDC’s weekly FluView surveillance system and provide additional information about ILI, and also about behaviors related to influenza.

How is the influenza BRFSS data about seasonal and 2009 H1N1 vaccinations being used this season?

Questions in BRFSS’s influenza vaccination module ask participants if they have gotten the seasonal and 2009 H1N1 vaccines.  The main purpose for collecting this data is to allow CDC to provide state level vaccination estimates.  A secondary purpose is to provide national estimates for smaller subgroups of the population, including different racial and ethnic groups, those with certain underlying medical conditions (such as asthma and diabetes) that place them at high risk for complications from the flu, and health care providers. 

Are there any limitations to the BRFSS data?

BRFSS data does have a few limitations.  Because it is a telephone survey, it does not reach people without telephones.  In addition, a majority of interviews are conducted by landlines; therefore households that use cell phones only are much less like to participate.  Additionally, these data are self-reported and therefore, as is the case with all self-reported data, their reliability is subject to question.


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