Estimating Influenza Disease Burden from Population-Based Surveillance Data in the United States

Abstract

Annual estimates of the influenza disease burden provide information to evaluate programs and allocate resources. We used a multiplier method with routine population-based surveillance data on influenza hospitalization in the United States to correct for under-reporting and estimate the burden of influenza for seasons after the 2009 pandemic. Five sites of the Influenza Hospitalization Surveillance Network (FluSurv-NET) collected data on the frequency and sensitivity of influenza testing during two seasons to estimate under-detection. Population-based rates of influenza-associated hospitalization and Intensive Care Unit admission from 2010–2013 were extrapolated to the U.S. population from FluSurv-NET and corrected for under-detection. Influenza deaths were calculated using a ratio of deaths to hospitalizations. We estimated that influenza-related hospitalizations were under-detected during 2010-11 by a factor of 2.1 (95%CI 1.7–2.9) for age < 18 years, 3.1 (2.4–4.5) for ages 18-64 years, and 5.2 (95%CI 3.8–8.3) for age 65+. Results were similar in 2011-12. Extrapolated estimates for 3 seasons from 2010–2013 included: 114,192–624,435 hospitalizations, 18,491–95,390 ICU admissions, and 4,915–27,174 deaths per year; 54–70% of hospitalizations and 71–85% of deaths occurred among adults aged 65+. Influenza causes a substantial disease burden in the U.S. that varies by age and season. Periodic estimation of multipliers across multiple sites and age groups improves our understanding of influenza detection in sentinel surveillance systems. Adjusting surveillance data using a multiplier method is a relatively simple means to estimate the impact of influenza and the subsequent value of interventions to prevent influenza.

Burden of influenza, respiratory syncytial virus, and other respiratory viruses and the completeness of respiratory viral identification among respiratory inpatients, Canada, 2003‐2014

“…A modeling study based on estimates of testing probabilities and test sensitivity by Reed et al10 calculated multipliers of 2, 3, and 5 for pediatric age group, working‐age adults, and adults aged 65+, respectively; however, these estimates were for the PNI diagnostic group only. Our estimated influenza multiplier for the pediatric age group of 1.3 (the multiplier is the reciprocal of completeness in Table 2) is lower than the US estimate.…”

“…Because regression estimates are not available in real time, researchers have proposed other methods10, 11 to use surveillance data to predict the full burden in near real time, only some of which have been evaluated at year‐end against a regression approach 6, 12, 13, 14…”

“…In this study, our objectives were (i) to update our estimates of the average annual respiratory hospitalization rate attributable to influenza, RSV, and other respiratory viruses in Canada by age group and disease severity; (ii) to quantify the degree to which the rates of hospitalizations coded as due to those virus rates underestimate this burden; and (iii) to discuss issues related to adopting emerging approaches based on near real‐time data that would permit more timely assessment of the burden of influenza and other respiratory viruses. The proportion of hospitalizations attributed to influenza and other respiratory viruses for which the respiratory virus was identified provides an approximate measure of completeness of viral identification, estimates that help hospital administrators interpret their data, as the corresponding multiplier (reciprocal of completeness) has been used in this way with near real‐time surveillance data 10. As estimation of the hospitalization burden attributable to influenza for the pediatric population has been a challenge, we explored this issue by comparing the number of admissions with the influenza virus identified to the estimated excess attributed to influenza for various diagnostic groups.…”

Epidemiology and burden of influenza in the U.S. Department of Veterans Affairs

“…Because not all persons with influenza sought medical care, and some sought treatment outside VA, we likely underestimated the true influenza burden in the VA patient population. Future analyses could account for influenza under‐detection by using a CDC multiplier method to adjust VA surveillance data 3. Administrative coding data were utilized for influenza hospitalizations, outpatient influenza and ILI visits, and telephone triage encounters.…”

“…A recent report estimated that from 2010 to 2016, annual U.S. influenza‐related illnesses ranged from 9.2 to 35.6 million, medical visits from 4.3 to 16.7 million, hospitalizations from 140 000 to 710 000, and pneumonia and influenza deaths from 4000 to 20 000 2. Although U.S. population‐based surveillance data have been used to estimate overall and age‐based influenza disease burden,2, 3, 4 the epidemiology and impact of seasonal influenza in more specific U.S. patient populations is less well described.…”