Improving Accuracy of Influenza-Associated Hospitalization Rate Estimates

Diagnostic test sensitivity affects rate estimates for laboratory-confirmed influenza–associated hospitalizations. We used data from FluSurv-NET, a national population-based surveillance system for laboratory-confirmed influenza hospitalizations, to capture diagnostic test type by patient age and influenza season. We calculated observed rates by age group and adjusted rates by test sensitivity. Test sensitivity was lowest in adults >65 years of age. For all ages, reverse transcription PCR was the most sensitive test, and use increased from 65 years. After 2009, hospitalization rates adjusted by test sensitivity were ≈15% higher for children 65 years of age. Test sensitivity adjustments improve the accuracy of hospitalization rate estimates

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

<div><p>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.</p></div

Distribution of influenza test types used and average sensitivity of influenza testing among hospitalized patients tested for influenza in six FluSurv-NET sites.

<p>Distribution of influenza test types used and average sensitivity of influenza testing among hospitalized patients tested for influenza in six FluSurv-NET sites.</p

Risk of severe influenza-associated outcomes among persons hospitalized with influenza by season and age group.

<p>* Calculated from FluSurv-NET surveillance data, all sites</p><p>**Among deaths coded as pneumonia, influenza, or acute lower respiratory tract infections in the 2010 and 2011 National Multiple Cause Mortality Files. 2012–13 is an average of the two years with available data.</p><p>*** Algebraic combination of the risk of death if hospitalized and the % of deaths that occur during a hospital admission. 95% confidence intervals were calculated by combining the associated binary uncertainty of each parameter.</p><p>Risk of severe influenza-associated outcomes among persons hospitalized with influenza by season and age group.</p

Estimated multiplier for under-detection of influenza among hospitalized persons in FluSurv-NET.

<p>The multiplier represents the number of estimated true influenza hospitalizations per reported hospitalization.</p><p><i>*Summary multipliers were calculated using the same methods as 2010–11 and 2011–12 but using all the data from both seasons</i>.</p><p>Estimated multiplier for under-detection of influenza among hospitalized persons in FluSurv-NET.</p

Estimates of influenza disease burden in rates per 100,000 and number per U.S. population by age group and influenza season, United States.

<p>Estimates of influenza disease burden in rates per 100,000 and number per U.S. population by age group and influenza season, United States.</p

Proportion of patients tested for influenza (with binomial 95% confidence interval) by age group among hospitalized patients with a respiratory infection* in six FluSurv-NET sites.

<p>Proportion of patients tested for influenza (with binomial 95% confidence interval) by age group among hospitalized patients with a respiratory infection* in six FluSurv-NET sites.</p

General framework for estimating influenza disease burden in the U.S. population using FluSurv-NET hospital-based influenza surveillance data.

<p>General framework for estimating influenza disease burden in the U.S. population using FluSurv-NET hospital-based influenza surveillance data.</p

Factors Associated with Severe Outcomes Among Immunocompromised Adults Hospitalized for COVID-19 - COVID-NET, 10 States, March 2020-February 2022.

Immunocompromised persons are at increased risk for severe COVID-19-related outcomes, including intensive care unit (ICU) admission and death (1). Data on adults aged ≥18 years hospitalized with laboratory-confirmed COVID-19 from 10 U.S. states in the COVID-19-Associated Hospitalization Surveillance Network (COVID-NET) were analyzed to assess associations between immunocompromise and ICU admission and in-hospital death during March 1, 2020-February 28, 2022. Associations of COVID-19 vaccination status with ICU admission and in-hospital death were also examined during March 1, 2021-February 28, 2022. During March 1, 2020-February 28, 2022, among a sample of 22,345 adults hospitalized for COVID-19, 12.2% were immunocompromised. Among unvaccinated patients, those with immunocompromise had higher odds of ICU admission (adjusted odds ratio [aOR]&nbsp;=&nbsp;1.26; 95% CI&nbsp;=&nbsp;1.08-1.49) and in-hospital death (aOR&nbsp;=&nbsp;1.34; 95% CI&nbsp;=&nbsp;1.05-1.70) than did nonimmunocompromised patients. Among vaccinated patients,* those with immunocompromise had higher odds of ICU admission (aOR&nbsp;=&nbsp;1.40; 95% CI&nbsp;=&nbsp;1.01-1.92) and in-hospital death (aOR = 1.87; 95% CI&nbsp;=&nbsp;1.28-2.75) than did nonimmunocompromised patients. During March 1, 2021-February 28, 2022, among nonimmunocompromised patients, patients who were vaccinated had lower odds of death (aOR&nbsp;=&nbsp;0.58; 95% CI&nbsp;=&nbsp;0.39-0.86) than did unvaccinated patients; among immunocompromised patients, odds of death between vaccinated and unvaccinated patients did not differ. Immunocompromised persons need additional protection from COVID-19 and using multiple known COVID-19 prevention strategies,† including nonpharmaceutical interventions, up-to-date vaccination of immunocompromised persons and their close contacts,§ early testing, and COVID-19 prophylactic (Evusheld) and early antiviral treatment,¶ can help prevent hospitalization and subsequent severe COVID-19 outcomes among immunocompromised persons

Laboratory-Confirmed COVID-19-Associated Hospitalizations Among Adults During SARS-CoV-2 Omicron BA.2 Variant Predominance - COVID-19-Associated Hospitalization Surveillance Network, 14 States, June 20, 2021-May 31, 2022.

Beginning the week of March 20–26, 2022, the Omicron BA.2 variant of SARS-CoV-2, the virus that causes COVID-19, became the predominant circulating variant in the United States, accounting for &gt;50% of sequenced isolates.* Data from the COVID-19–Associated Hospitalization Surveillance Network (COVID-NET) were analyzed to describe recent COVID-19–associated hospitalization rates among adults aged ≥18 years during the period coinciding with BA.2 predominance (BA.2 period [Omicron BA.2 and BA.2.12.1; March 20–May 31, 2022]). Weekly hospitalization rates (hospitalizations per 100,000 population) among adults aged ≥65 years increased threefold, from 6.9 (week ending April 2, 2022) to 27.6 (week ending May 28, 2022); hospitalization rates in adults aged 18–49 and 50–64 years both increased 1.7-fold during the same time interval. Hospitalization rates among unvaccinated adults were 3.4 times as high as those among vaccinated adults. Among hospitalized nonpregnant patients in this same period, 39.1% had received a primary vaccination series and 1 booster or additional dose; 5.0% had received a primary series and ≥2 boosters or additional doses. All adults should stay up to date† with COVID-19 vaccination, and multiple nonpharmaceutical and medical prevention measures should be used to protect those at high risk for severe COVID-19 illness, irrespective of vaccination status§ (1).Beginning the week of March 20–26, 2022, the Omicron BA.2 variant of SARS-CoV-2, the virus that causes COVID-19, became the predominant circulating variant in the United States, accounting for &gt;50% of sequenced isolates.* Data from the COVID-19–Associated Hospitalization Surveillance Network (COVID-NET) were analyzed to describe recent COVID-19–associated hospitalization rates among adults aged ≥18 years during the period coinciding with BA.2 predominance (BA.2 period [Omicron BA.2 and BA.2.12.1; March 20–May 31, 2022]). Weekly hospitalization rates (hospitalizations per 100,000 population) among adults aged ≥65 years increased threefold, from 6.9 (week ending April 2, 2022) to 27.6 (week ending May 28, 2022); hospitalization rates in adults aged 18–49 and 50–64 years both increased 1.7-fold during the same time interval. Hospitalization rates among unvaccinated adults were 3.4 times as high as those among vaccinated adults. Among hospitalized nonpregnant patients in this same period, 39.1% had received a primary vaccination series and 1 booster or additional dose; 5.0% had received a primary series and ≥2 boosters or additional doses. All adults should stay up to date† with COVID-19 vaccination, and multiple nonpharmaceutical and medical prevention measures should be used to protect those at high risk for severe COVID-19 illness, irrespective of vaccination status§ (1)