Ashley Fowlkes1, Andrea Steffens1, Jon Temte2, Steve Di Lonardo3, Lisa McHugh4, Karen Martin5, Heather Rubino6, Michelle Feist7, Carol Davis8, Christine Selzer9, Jose Lojo10, Oluwakemi Oni11, Katie Kurkjian12, Ann Thomas13, Rachelle Boulton14, Nicole Bryan15, Ruth Lynfield5, Matthew Biggerstaff1, Lyn Finelli1. 1. Influenza Division, Centers for Disease Control and Prevention, Atlanta, GA, USA. 2. Department of Family Medicine, University of Wisconsin School of Medicine and Public Health, Madison, WI, USA. 3. Division of Prevention and Primary Care, New York City Department of Health and Mental Hygiene, Gotham Center, Long Island City, NY, USA. 4. Communicable Disease Service Infectious and Zoonotic Disease, New Jersey Department of Health, Trenton, NJ, USA. 5. Minnesota Department of Health, St Paul, MN, USA. 6. Bureau of Epidemiology, Florida Department of Health, Tallahassee, FL, USA. 7. Division of Disease Control, North Dakota Department of Health, Bismarck, ND, USA. 8. Public Health Preparedness and Epidemiology Program, Texas Department of Health, Temple, TX, USA. 9. Acute Communicable Disease Control Program, Los Angeles County Department of Public Health, Los Angeles, CA, USA. 10. Division of Disease Control, Philadelphia Department of Public Health, Philadelphia, PA, USA. 11. Center for Acute Disease Epidemiology, Iowa Department of Public Health, Des Moines, IA, USA. 12. Division of Surveillance and Investigation, Virginia Department of Health, Richmond, VA, USA. 13. Acute and Communicable Disease Program, Oregon Public Health Division, Portland, OR, USA. 14. Division of Disease Control and Prevention, Utah Department of Health, Salt Lake City, UT, USA. 15. Council of State and Territorial Epidemiologists, Atlanta, GA, USA. Electronic address: afowlkes@cdc.gov.
Abstract
BACKGROUND: Since the introduction of pandemic influenza A (H1N1) to the USA in 2009, the Influenza Incidence Surveillance Project has monitored the burden of influenza in the outpatient setting through population-based surveillance. METHODS: From Oct 1, 2009, to July 31, 2013, outpatient clinics representing 13 health jurisdictions in the USA reported counts of influenza-like illness (fever including cough or sore throat) and all patient visits by age. During four years, staff at 104 unique clinics (range 35-64 per year) with a combined median population of 368,559 (IQR 352,595-428,286) attended 35,663 patients with influenza-like illness and collected 13,925 respiratory specimens. Clinical data and a respiratory specimen for influenza testing by RT-PCR were collected from the first ten patients presenting with influenza-like illness each week. We calculated the incidence of visits for influenza-like illness using the size of the patient population, and the incidence attributable to influenza was extrapolated from the proportion of patients with positive tests each week. FINDINGS: The site-median peak percentage of specimens positive for influenza ranged from 58.3% to 77.8%. Children aged 2 to 17 years had the highest incidence of influenza-associated visits (range 4.2-28.0 per 1000 people by year), and adults older than 65 years had the lowest (range 0.5-3.5 per 1000 population). Influenza A H3N2, pandemic H1N1, and influenza B equally co-circulated in the first post-pandemic season, whereas H3N2 predominated for the next two seasons. Of patients for whom data was available, influenza vaccination was reported in 3289 (28.7%) of 11,459 patients with influenza-like illness, and antivirals were prescribed to 1644 (13.8%) of 11,953 patients. INTERPRETATION: Influenza incidence varied with age groups and by season after the pandemic of 2009 influenza A H1N1. High levels of influenza virus circulation, especially in young children, emphasise the need for additional efforts to increase the uptake of influenza vaccines and antivirals. FUNDING: US Centers for Disease Control and Prevention.
BACKGROUND: Since the introduction of pandemic influenza A (H1N1) to the USA in 2009, the Influenza Incidence Surveillance Project has monitored the burden of influenza in the outpatient setting through population-based surveillance. METHODS: From Oct 1, 2009, to July 31, 2013, outpatient clinics representing 13 health jurisdictions in the USA reported counts of influenza-like illness (fever including cough or sore throat) and all patient visits by age. During four years, staff at 104 unique clinics (range 35-64 per year) with a combined median population of 368,559 (IQR 352,595-428,286) attended 35,663 patients with influenza-like illness and collected 13,925 respiratory specimens. Clinical data and a respiratory specimen for influenza testing by RT-PCR were collected from the first ten patients presenting with influenza-like illness each week. We calculated the incidence of visits for influenza-like illness using the size of the patient population, and the incidence attributable to influenza was extrapolated from the proportion of patients with positive tests each week. FINDINGS: The site-median peak percentage of specimens positive for influenza ranged from 58.3% to 77.8%. Children aged 2 to 17 years had the highest incidence of influenza-associated visits (range 4.2-28.0 per 1000 people by year), and adults older than 65 years had the lowest (range 0.5-3.5 per 1000 population). InfluenzaA H3N2, pandemic H1N1, and influenza B equally co-circulated in the first post-pandemic season, whereas H3N2 predominated for the next two seasons. Of patients for whom data was available, influenza vaccination was reported in 3289 (28.7%) of 11,459 patients with influenza-like illness, and antivirals were prescribed to 1644 (13.8%) of 11,953 patients. INTERPRETATION:Influenza incidence varied with age groups and by season after the pandemic of 2009 influenzaA H1N1. High levels of influenza virus circulation, especially in young children, emphasise the need for additional efforts to increase the uptake of influenza vaccines and antivirals. FUNDING: US Centers for Disease Control and Prevention.
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