Respiratory symptoms in households as an effective marker for influenza-like illness surveillance in the community

Abstract

To effectively track the growth of influenza, we piloted an online system to monitor influenza-like illness (ILI) in the community in one district of Hong Kong. Four syndromic markers, namely fever, respiratory symptoms, fever with respiratory symptoms, fever and/or respiratory symptoms, either of the individual or of the household, were collected during the study period from June 2012 to October 2013. A total of 132 residents of Tuen Mun District reported syndromic markers at the individual and household levels on a weekly basis. Temporal patterns of these markers were compared with data derived from laboratory surveillance by dynamic linear regression. Household respiratory symptoms were found to be an effective syndromic marker, pre-dating overall laboratory virus surveillance results on influenza diseases in two influenza seasons by 3-4 weeks. To conclude, respiratory symptoms can be a good marker predicting the onset of the influenza season in the community, and is particularly useful with regard to data from households, even if the sample size may not be a large one.

Keywords: ILI; Influenza; Influenza-like illness; Syndromic surveillance.