Surveillance for Infuenza
Surveillance in the United States and around the world is an important step in identifying possible influenza epidemics and classifying which influenza strains go into the yearly vaccines. There are 136 national influenza centers in over 100 countries worldwide that conduct year-round surveillance of influenza, and all information on trends and strains are reported to five World Health Organization Collaborating Centers for Reference and Research on Influenza in the United States, the United Kingdom, Australia, Japan and China.
In the United States, the Epidemiology and Prevention Branch in the Influenza Division of the CDC deals with analyzing influenza activity every year. Over 80 laboratories in the United States and abroad provide information on virologic surveillance, including the total number of respiratory specimens tested and the number positive for influenza types A and B each week (Center for Disease Control and Prevention, 2011). Hospitals and healthcare facilities also provide numerous influenza cases to the CDC, thereby providing up-to-date prevalence and incidence rates in all 50 states. Mortality and hospitalization surveillance track the number of influenza-related deaths and the number of patients admitted to hospitals with laboratory-confirmed influenza, respectively. Lastly, the surveillance system also tracks the geographic spread of influenza. All of this information is important in controlling influenza mutations, identifying strains for the yearly vaccinations and categorizing susceptible populations.
The figure below shows the percentage of visits to US outpatient facilities for influenza-like illness by month and shows how it varies during the year.
Source: http://www.cdc.gov/flu/weekly/summary.htm/
Syndromic surveillance uses indicators from individuals and populations before laboratory results and confirmed diagnoses to identify outbreaks and to monitor the health status of the community (Center for Disease Control and Prevention, 2011). This type of surveillance is important because it more up-to-date and often provides information quicker than a laboratory test can be completed.
Current weekly reports on influenza activity in the US can be found at http://www.cdc.gov/flu/weekly/, while worldwide reports may be accessed at http://www.who.int/influenza/gisrs_laboratory/flunet/en/. Google Flu Trends uses aggregated search data to estimate influenza activity around the world - http://www.google.org/flutrends/