How CDC is monitoring influenza data among people to better understand the current avian influenza A (H5N1) situation

Systems Used to Monitor Influenza Activity

Influenza activity is monitored year-round using multiple systems. These systems are used for monitoring seasonal influenza and, because influenza viruses are constantly changing in small, and occasionally more significant ways, these systems are also useful for monitoring signals and trends from novel influenza virus infections. Some examples are provided below.

Monitoring for Changes in Tests Positive for Influenza in Clinical Settings

Approximately 300 clinical laboratories located throughout all 50 states, Puerto Rico, Guam, and the District of Columbia report the results of clinical testing for influenza through either the U.S. WHO Collaborating Laboratories System or the National Respiratory and Enteric Virus Surveillance System (NREVSS). The results of tests performed by clinical laboratories nationwide are summarized below. While these laboratories don’t test specifically for influenza A(H5N1) virus, by tracking the percentage of specimens tested that are positive for influenza A viruses, we can monitor for unusual increases in influenza activity that may be an early sign of spread of novel influenza A viruses, including H5N1.

Monitoring for Changes in Emergency Department Visits for Influenza

The National Syndromic Surveillance Program (NSSP) collects, analyzes, and shares electronic data received from multiple health care settings, including emergency departments (ED). Data from NSSP on the weekly percentage of total emergency department visits associated with influenza-related diagnoses are summarized below. It’s important to note that these visits are among persons with any influenza diagnosis and are not specific to H5N1. However, by tracking all influenza diagnoses, as well as symptoms potentially related to influenza virus infections, among patients in EDs, the chance of detecting unusual levels of influenza is improved, including in jurisdictions where the virus has been identified in people or animals.