1118. The Incidence of Medically-attended Influenza-like Illness and Influenza Virus Infection Across the Age Span: New Insights in the Epidemiology of Laboratory-confirmed Influenza
Session: Poster Abstract Session: Influenza and H1N1 Diagnosis, Epidemiology, and Viral Outcome
Saturday, October 22, 2011
Room: Poster Hall B1

Early serologic studies have shown that school-age children have the highest incidence of influenza, but age-specific incidence differed by influenza type and subtype. Molecular diagnostic tests vastly improve specificity and allow for rapid determination of circulating strains. The Influenza Incidence Surveillance Project (IISP) estimates the incidence of medically-attended influenza-like illness (ILI) and influenza virus type- and subtype-specific by age using molecular methods.


From August 2010 through April 2011, 55 health care providers in 12 states and jurisdictions conducted prospective surveillance of patients with acute respiratory infection and ILI (fever with cough and/or sore throat). Respiratory specimens were collected for influenza testing by real-time reverse transcriptase polymerase chain reaction (RT-PCR) or multiplex RT-PCR from the first 10 ILI patients each week; demographic and clinical data were collected. The incidence of influenza infection was estimated by multiplying the proportion influenza positive by the number of ILI cases reported each week with the total patient population as the denominator.


During the surveillance period, 364,817 outpatient visits occurred, of which 2.1% were visits for ILI. ILI activity peaked from 23 January to 19 February 2011. While ILI incidence was highest among children aged 2-4 years, laboratory-confirmed influenza was highest among children aged 5-17 years. Influenza type and subtype incidence differed by age with influenza A (H3N2) and influenza B having the highest incidence among the 5-17 year age group, while incidence of influenza A (H1N1) was highest in the 18-24 year age group. There was an absence of influenza A (H1N1) in persons aged >65 years.


Influenza rates were highest in school-age children for influenza A (H3N2) and influenza B, but not influenza A (H1N1), perhaps due to immunity acquired during the pandemic when influenza A (H1N1) circulated widely in this age group. Children aged <5 years were less likely to have influenza, and may reflect social mixing patterns in this age group. IISP provides a platform for a greater understanding of the spectrum of influenza disease and epidemiology.

Subject Category: V. Virology including clinical and basic studies of viral infections, including hepatitis

Ashley Fowlkes, MPH1,2, Heidi Davidson, MPH1, Lisa Ferland, MPH3, Kate Goodin, MPH4, Yumei Sun, PhD5, Sovirny Norng, MPH6, Karen Martin, MPH7, Michelle Feist8, Steve Di Lonardo, MS9, Lisa McHugh, MPH10, Jose Lojo, MPH11, Rachel Linz, MPH12, Rachelle Boulton, MSPH13, Katie Kurkjian, DVM, MPH1,14, Jonathan Temte, MD, PhD15 and Lyn Finelli, DrPH, MS1, (1)Centers for Disease Control and Prevention, Atlanta, GA, (2)Influenza Division, Centers for Disease Control and Prevention, Atlanta, GA, (3)Council of State and Territorial Epidemiologists, Atlanta, GA, (4)Florida Department of Health, Tallahassee,, FL, (5)Iowa Department of Public Health, Des Moines, ID, (6)Los Angeles County Department of Public Health, Los Angeles, CA, (7)Minnesota Department of Health, St. Paul, MN, (8)North Dakota Department of Health, Bismarck,, ND, (9)New York City Department of Health and Mental Hygiene, Long Island City , NY, (10)New Jersey Department of Health and Senior Services, Trenton, NJ, (11)Philadelphia Department of Public Health, Philadelphia , PA, (12)Oregon Public Health Division, Portland, OR, (13)Utah Department of Health, Salt Lake City, UT, (14)Virginia Department of Health, Richmond, VA, (15)University of Wisconsin School of Medicine and Public Health, Madison, WI


A. Fowlkes, None

H. Davidson, None

L. Ferland, None

K. Goodin, None

Y. Sun, None

S. Norng, None

K. Martin, None

M. Feist, None

S. Di Lonardo, None

L. McHugh, None

J. Lojo, None

R. Linz, None

R. Boulton, None

K. Kurkjian, None

J. Temte, None

L. Finelli, None

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