Estimating severity of influenza epidemics from severe acute respiratory infections (SARI) in intensive care units

Liselotte van Asten,Angie Luna Pinzon,Nicolette F. de Keizer,Gé A. Donker,Evert de Jonge,Dylan W. de Lange,Sierk Marbus,Frederika Dijkstra,Wim van der Hoek

doi:10.1186/s13054-018-2274-8

Abstract

BackgroundWhile influenza-like-illness (ILI) surveillance is well-organized at primary care level in Europe, few data are available on more severe cases. With retrospective data from intensive care units (ICU) we aim to fill this current knowledge gap. Using multiple parameters proposed by the World Health Organization we estimate the burden of severe acute respiratory infections (SARI) in the ICU and how this varies between influenza epidemics.MethodsWe analyzed weekly ICU admissions in the Netherlands (2007–2016) from the National Intensive Care Evaluation (NICE) quality registry (100% coverage of adult ICUs in 2016; population size 14 million) to calculate SARI incidence, SARI peak levels, ICU SARI mortality, SARI mean Acute Physiology and Chronic Health Evaluation (APACHE) IV score, and the ICU SARI/ILI ratio. These parameters were calculated both yearly and per separate influenza epidemic (defined epidemic weeks). A SARI syndrome was defined as admission diagnosis being any of six pneumonia or pulmonary sepsis codes in the APACHE IV prognostic model. Influenza epidemic periods were retrieved from primary care sentinel influenza surveillance data.ResultsAnnually, an average of 13% of medical admissions to adult ICUs were for a SARI but varied widely between weeks (minimum 5% to maximum 25% per week). Admissions for bacterial pneumonia (59%) and pulmonary sepsis (25%) contributed most to ICU SARI. Between the eight different influenza epidemics under study, the value of each of the severity parameters varied. Per parameter the minimum and maximum of those eight values were as follows: ICU SARI incidence 558–2400 cumulated admissions nationwide, rate 0.40–1.71/10,000 inhabitants; average APACHE score 71–78; ICU SARI mortality 13–20%; ICU SARI/ILI ratio 8–17 cases per 1000 expected medically attended ILI in primary care); peak-incidence 101–188 ICU SARI admissions in highest-incidence week, rate 0.07–0.13/10,000 population).ConclusionsIn the ICU there is great variation between the yearly influenza epidemic periods in terms of different influenza severity parameters. The parameters also complement each other by reflecting different aspects of severity. Prospective syndromic ICU SARI surveillance, as proposed by the World Health Organization, thereby would provide insight into the severity of ongoing influenza epidemics, which differ from season to season.

Highlights

Though advocated by the World Health Organization (WHO) and the European Centre for Disease Prevention and Control (ECDC), surveillance of severe acute respiratory infections (SARI) that require hospital admission is implemented in only few Western European countries [1,2,3,4]
Analyses We described incidence of intensive care units (ICU) SARI admissions during complete season-years and we described ICU SARI characteristics during defined influenza epidemics: incidence, rate, the contribution of the separate diagnoses to the syndrome, mean Acute Physiology and Chronic Health Evaluation (APACHE) IV score, in-ICU SARI mortality, ICU SARI peak incidence, and the SARI/ILI ratio
Year-to-year and week-to-week ICU SARI admissions The overall proportion of ICU SARI admissions were relatively stable from one season-year to the (11– 14% of all ICU medical admissions were a SARI, Table 1), This proportion varied more from one week to the

Summary

Introduction

Though advocated by the World Health Organization (WHO) and the European Centre for Disease Prevention and Control (ECDC), surveillance of severe acute respiratory infections (SARI) that require hospital admission is implemented in only few Western European countries [1,2,3,4]. Surveillance of acute respiratory infections (ARI) or influenza-like illness (ILI) in primary care is well-established as part of the European Influenza Surveillance Network (EISN), coordinated by the ECDC [5, 6]. Such primary care surveillance covers the community dwelling population and is focused on patients with milder illness. While influenza-like-illness (ILI) surveillance is well-organized at primary care level in Europe, few data are available on more severe cases. Using multiple parameters proposed by the World Health Organization we estimate the burden of severe acute respiratory infections (SARI) in the ICU and how this varies between influenza epidemics

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