Using a hospital admission survey to estimate the burden of influenza-associated severe acute respiratory infection in one province of Cambodia-methods used and lessons learned.

Rebekah J Stewart,Borann Sar,Chiedza Machingaidze,Ann Moen,Erica Dueger,Vanra Ieng,Reiko Tsuyuoka,Sovann Ly,Kheng Sim,A Danielle Iuliano,Katherine Roguski,Seng Heng

doi:10.1111/irv.12489

Abstract

BackgroundUnderstanding the burden of influenza‐associated severe acute respiratory infection (SARI) is important for setting national influenza surveillance and vaccine priorities. Estimating influenza‐associated SARI rates requires hospital‐based surveillance data and a population‐based denominator, which can be challenging to determine.ObjectivesWe present an application of the World Health Organization's recently developed manual (WHO Manual) including hospital admission survey (HAS) methods for estimating the burden of influenza‐associated SARI, with lessons learned to help others calculate similar estimates.MethodsUsing an existing SARI surveillance platform in Cambodia, we counted influenza‐associated SARI cases during 2015 at one sentinel surveillance site in Svay Rieng Province. We applied WHO Manual‐derived methods to count respiratory hospitalizations at all hospitals within the catchment area, where 95% of the sentinel site case‐patients resided. We used HAS methods to adjust the district‐level population denominator for the sentinel site and calculated the incidence rate of influenza‐associated SARI by dividing the number of influenza‐positive SARI infections by the adjusted population denominator and multiplying by 100 000. We extrapolated the rate to the provincial population to derive a case count for 2015. We evaluated data sources, detailed steps of implementation, and identified lessons learned.ResultsWe estimated an adjusted influenza‐associated 2015 SARI rate of 13.5/100 000 persons for the catchment area of Svay Rieng Hospital and 77 influenza‐associated SARI cases in Svay Rieng Province after extrapolation.ConclusionsMethods detailed in the WHO Manual and operationalized successfully in Cambodia can be used in other settings to estimate rates of influenza‐associated SARI.

Highlights

Influenza is an acute viral infection and a significant contributor to global morbidity[1-3] and mortality.[4,5] While the burden of influenza has been established in some countries, it is not well understood in many others, lower-middle-income countries such as Cambodia.[6]
The World Health Organization’s (WHO) global standards for influenza surveillance are used by many countries.[8-11]
We present an application in one province of Cambodia using hospital admission survey (HAS) methods to estimate the population of the catchment area and calculate the burden of influenza-associated Severe acute respiratory infection (SARI)

Summary

Introduction

Influenza is an acute viral infection and a significant contributor to global morbidity[1-3] and mortality.[4,5] While the burden of influenza has been established in some countries, it is not well understood in many others, lower-middle-income countries such as Cambodia.[6]. Understanding the burden of influenza-associated severe acute respiratory infection (SARI) is important for setting national influenza surveillance and vaccine priorities. Estimating influenza-associated SARI rates requires hospital-based surveillance data and a population-based denominator, which can be challenging to determine. Objectives: We present an application of the World Health Organization’s recently developed manual (WHO Manual) including hospital admission survey (HAS) methods for estimating the burden of influenza-associated SARI, with lessons learned to help others calculate similar estimates. Methods: Using an existing SARI surveillance platform in Cambodia, we counted influenza-associated SARI cases during 2015 at one sentinel surveillance site in Svay Rieng Province.

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