Self-Reported Influenza-Like Illness and Receipt of Influenza Antiviral Drugs During the 2009 Pandemic, United States, 2009–2010

Abstract

Objectives. The purpose of our study was to more accurately characterize people reporting influenza-like illness (ILI) and evaluate trends in health care seeking and influenza diagnosis and treatment during the 2009 influenza pandemic. Methods. From September 2009 to March 2010, we ascertained ILI (fever with cough or sore throat), health care seeking, and clinical diagnosis and treatment of influenza with influenza antiviral drugs among adults in 51 jurisdictions, and ILI and health care seeking among children in 41 jurisdictions. Results. Among 216 431 adults and 43 511 children, 8.1% and 28.4% reported ILI, respectively. ILI peaked during November interviews and was higher among young people and American Indian/Alaska Natives. Of those with ILI, 40% of adults and 56% of children reported seeking health care; 26% of adults who sought care reported receiving a diagnosis of influenza. Of adults reporting an influenza diagnosis, 36% were treated with influenza antiviral drugs; treatment was highest among adults aged 18 to 49 years. Conclusions. Analysis of ILI data from the Behavioral Risk Factor Surveillance System enabled a better understanding of the factors associated with self-reported ILI, health care seeking, and clinical influenza diagnosis and treatment, and will help inform year-to-year influenza trends.

Estimates of the Number of Human Infections With Influenza A(H3N2) Variant Virus, United States, August 2011–April 2012

“…Although the proportion of respondents with ILI who sought care has remained consistent during the two study periods, the proportion of persons with influenza specimens collected during the summer months is more likely to differ. Persons may either have fewer respiratory specimens collected overall or be tested less frequently for influenza but more frequently for pathogens associated with transmission during the summer months (e.g., pertussis) [4, 5]. Therefore, the proportion of specimens collected for influenza testing used in this analysis may be too high and the resulting under-ascertainment multiplier too low.…”

“…To estimate the proportion of persons with ILI who visited healthcare providers and had an influenza respiratory specimen collected (parameters A and C), we analyzed survey data from the Behavioral Risk Factor Surveillance System (BRFSS) influenza-like illness (ILI) module from the 2009–10 and 2010–11 influenza seasons [4]. To estimate the proportion of persons who visited healthcare providers participating in voluntary influenza surveillance programs (e.g., a U.S. Outpatient Influenza-Like Illness Surveillance Network [ILINet] physician, a hospital, or a healthcare site conducting a special study of influenza) (parameter B), we used ILINet catchment as a proxy [9].…”

“…We generated median and upper and lower 90% values for the number of total cases of illness. Because care seeking for ILI varies based on the age of the patient, we stratified the model between pediatric (<18 years old) and adult (≥18 years old) cases [4]. …”

“… * BRFSS: Behavioral Risk Factor Surveillance System, [4] ** ILINet: Influenza Like Illness Network, [9] …”

“…Among these, less than half of all people with influenza-like illness (ILI) seek health care; when health care is sought, providers test few patients for influenza; point of care rapid influenza antigen diagnostic tests have low test sensitivity and are not able to differentiate H3N2v virus from the currently circulating seasonal influenza A virus strains, and a majority of healthcare providers do not forward respiratory specimens to their public health laboratory, thereby preventing further characterization and confirmation [4-7]. Therefore, the true number of H3N2v virus infections is likely much higher than reported.…”