The Aggregate Hospitalizations and Deaths Reporting Activity (AHDRA) is a web-based influenza surveillance system implemented in response to the 2009 H1N1 pandemic that collects voluntary reports of influenza-related hospitalizations and deaths from U.S. states and territories. (This system does not collect reports of individual cases of flu illness, only hospitalizations and deaths.)

The primary goal of state-level reporting of influenza hospitalizations and deaths is to track the progression of influenza activity within each state and to determine trends (increasing or decreasing).

AHDRA tracks flu-related hospitalizations and deaths, not just those related to 2009 H1N1.  State and local health departments do not need to report the type of influenza virus identified for each hospitalization or death.  Approximately 44 jurisdictions report to AHDRA on average each week.

State and local health departments can submit influenza-related hospitalization and death reports to AHDRA using a laboratory-confirmed case definition or a syndromic case definition.
(Specific guidance for state and local health departments is available at http://www.cdc.gov/H1N1flu/hospitalreporting.htm )

• Laboratory-confirmed hospitalizations represent patients who test positive for any type of influenza by a laboratory test, by rapid influenza test, RT-PCR, DFA, or viral culture. 
• Laboratory-confirmed deaths represent individuals whose deaths have been confirmed by a laboratory test as being associated with influenza.
• Syndromic hospitalizations represent patients whose hospitalizations have been clinically identified as being associated with influenza-like illness (ILI) or pneumonia syndrome. 
• Syndromic deaths represent individuals whose deaths have been clinicially-identified as being associated with influenza-like illness (ILI) or pneumonia syndrome.

More information about AHDRA and a summary and interpretation of AHDRA data collected during the 2009 H1N1 pandemic (April 2009 -January 30, 2010) is available at http://www.cdc.gov/H1N1flu/hosp_deaths_ahdra.htm and will be updated as developments warrant.

Information on the proportion of influenza viruses that are 2009 H1N1 versus seasonal influenza is reported from the virologic surveillance system through FluView (http://www.cdc.gov/flu/weekly).