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Influenza Surveillance Information

Eye on Influenza Newsletter

Seasonal Influenza Information

(last updated 5/17/2013)

Annual influenza epidemics follow a winter seasonal pattern in the United States with typical activity peaking during late December to March. Surveillance of influenza activity is important to guide prevention and control activities, vaccine strain selection, and patient care. In addition, surveillance activities help to monitor and prepare for the impact of influenza on the healthcare system. Influenza surveillance in California is particularly important to monitor for importation of novel strains of influenza due to our coastal location with several ports of entry for flights and shipping from Asia, as well as our other international borders.

Surveillance for influenza activity in Orange County includes the monitoring of the following components year-round:

  • influenza viruses:  specimens are submitted from participating hospitals, physicians, and laboratories for tracking and strain-typing
  • influenza-like illnesses:  sentinel providers (physicians, nurse practitioners, physician assistants) report outpatient influenza-like illnesses and submit specimens
  • pneumonia and influenza deaths:  death certificates are reviewed for deaths from pneumonia or influenza
  • emergency room saturation:  the hours that emergency rooms are "on diversion" or closed to new patients because of saturation
  • severe influenza and deaths:  are reported by health care providers and hospital infection control professionals
  • outbreaks of respiratory illness:  are investigated and control measures are instituted.
  • enhanced surveillance for human cases of avian influenza:  health care providers are requested to report any patients with fever and respiratory symptoms who traveled to affected areas in the 7-10 days prior to symptom onset (specific criteria will be distributed as novel strains are identified).

In addition, data on hospital admissions for pneumonia and influenza from one Orange County hospital is included in the California Department of Public Health weekly influenza report. Data from all these components are analyzed weekly, summarized, and compared with state and national trends.  Other enhanced surveillance may be implemented as needed similar to what was done in 2009-2010 during the 2009 H1N1 pandemic. 

For information on statewide influenza activity, see the California Influenza Surveillance Project webpage

For information on national influenza activity, see the CDC Flu Activity & Surveillance webpage.

Variant Influenza A H3N2 (H3N2v) in Humans

(last updated 5/17/2013) 

Human cases of swine-origin variant influenza A H3N2 (H3N2v) were reported in the U.S. in 2011-2012. Signs and symptoms of H3N2v infection are similar to that of seasonal influenza. This virus was first identified in July 2011 and contains the matrix (M) gene from the influenza A (H1N1)pdm09 virus which may confer increased transmissibility to and among humans, compared to other variant influenza strains. Most cases had direct or indirect exposure to pigs. Thus far only limited human-human transmission has occurred. No H3N2v cases have been identified to date in California. Note: Flu viruses are not spread by eating properly handled or prepared pork or pork products. For more information and current interim recommendations, see the recent issues of Eye on Influenza. For CDC updates and case counts, see the CDC H3N2v webpage. 

For Physicians and Other Health Care Providers

We are actively recruiting physicians and other health care providers to participate as sentinel providers for influenza surveillance. For more information, please To receive our influenza newsletter, please email

Additional information available on our For Physicians Page.