Evaluation of an influenza-like illness case definition in the diagnosis of influenza among patients with acute febrile illness in cambodia

Matthew R Kasper,Thomas F Wierzba,Ly Sovann,Shannon D Putnam,Patrick J Blair

doi:10.1186/1471-2334-10-320

Matthew R Kasper, Thomas F Wierzba + Show 3 more

Open Access

https://doi.org/10.1186/1471-2334-10-320

Copy DOI

Abstract

BackgroundInfluenza-like illness (ILI) is often defined as fever (>38.0°C) with cough or sore throat. In this study, we tested the sensitivity, specificity, and positive and negative predictive values of this case definition in a Cambodia patient population.MethodsPassive clinic-based surveillance was established at nine healthcare centers to identify the causes of acute undifferentiated fever in patients aged two years and older seeking treatment. Fever was defined as tympanic membrane temperature >38°C lasting more than 24 hours and less than 10 days. Influenza virus infections were identified by polymerase chain reaction.ResultsFrom July 2008 to December 2008, 2,639 patients were enrolled. From 884 (33%) patients positive for influenza, 652 presented with ILI and 232 acute fever patients presented without ILI. Analysis by age group identified no significant differences between influenza positive patients from the two groups. Positive predictive values (PPVs) varied during the course of the influenza season and among age groups.ConclusionThe ILI case definition can be used to identify a significant percentage of patients with influenza infection during the influenza season in Cambodia, assisting healthcare providers in its diagnosis and treatment. However, testing samples based on the criteria of fever alone increased our case detection by 34%.

Highlights

Influenza-like illness (ILI) is often defined as fever (>38.0°C) with cough or sore throat
Building upon previous influenza surveillance results from rural Cambodian patients [19], we evaluated a commonly used ILI definition, document fever and cough or sore throat as a predictor of influenza disease
We found that the ILI case definition was more sensitive for patients infected with influenza A than influenza B, possibly reflecting milder disease among those infected influenza B as described in previous studies [20,21]

Summary

Introduction

Influenza-like illness (ILI) is often defined as fever (>38.0°C) with cough or sore throat. It is reported that between 3 and 5 million cases of severe influenza disease occur each year [1], with estimated annual influenza-associated mortality between 500,000 and 1,000,000 cases (median case-fatality of 190 deaths per 100,000 person infected with influenza) [2,3]. Common clinical symptoms of influenza include fever, cough, sore throat, headache, Building upon previous influenza surveillance results from rural Cambodian patients [19], we evaluated a commonly used ILI definition, document fever and cough or sore throat as a predictor of influenza disease. As previous studies have suggested limiting the use of clinical predictors for influenza to the influenza season [15], the sampling included all eligible patients enrolled during a single Cambodian influenza season

Methods

Results

Discussion

Conclusion