Age- and influenza activity-stratified case definitions of influenza-like illness: Experience from hospital-based influenza surveillance in South Korea

Tae Un Yang, Hee-Jin Cheong, Joon-Young Song, Jin Soo Lee, Seong Heon Wie, Young Keun Kim, Wonseok Choi, Jacob Lee, Hye Won Jeong, Woo Joo Kim

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Objectives: This study aims to identify clinical case definitions of influenza with higher accuracy in patients stratified by age group and influenza activity using hospital-based surveillance system. Methods: In seven tertiary hospitals across South Korea during 2011-2012 influenza season, respiratory specimens were obtained from patients presenting an influenza-like illness (ILI), defined as having fever plus at least one of following symptoms: cough, sore throat or rhinorrhea. Influenza was confirmed by reverse transcriptase-polymerase chain reaction. We performed multivariate logistic regression analyses to identify clinical variables with better relation with laboratory-confirmed influenza, and compared the accuracy of combinations. Results: Over the study period, we enrolled 1417 patients, of which 647 had laboratory-confirmed influenza. Patients with cough, rhinorrhea, sore throat or headache were more likely to have influenza (p<0.05). The most accurate criterion across the study population was the combination of cough, rhinorrhea, sore throat and headache (sensitivity 71.3%, specificity 60.1% and AUROC 0.66). The combination of rhinorrhea, sore throat and sputum during the peak influenza activity period in the young age group showed higher accuracy than that using the whole population (sensitivity 89.3%, specificity 72.1%, and AUROC 0.81). Conclusions: The accuracy of clinical case definitions of influenza differed across age groups and influenza activity periods. Categorizing the entire population into subgroups would improve the detection of influenza patients in the hospital-based surveillance system.

Original languageEnglish
Article numbere84873
JournalPLoS One
Issue number1
Publication statusPublished - 2014 Jan 24


ASJC Scopus subject areas

  • Biochemistry, Genetics and Molecular Biology(all)
  • Agricultural and Biological Sciences(all)

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