Internet-based monitoring of influenza-like illness in the general population: Experience of five influenza seasons in the Netherlands

Abstract

Like in most other countries, influenza surveillance in The Netherlands is based upon influenza-like illness (ILI) consultations reported by sentinel general practitioners (GP). In addition, an internet-based monitoring of ILI in the general population started in 2003/2004 (Great Influenza Survey (GIS)). We compared GIS results over 5 influenza seasons with results from the GP system. Weekly ILI incidence from GIS correlated well with ILI incidence from the GP system the same week and even better 1 week later. This suggests that GIS is useful for early detection of trends in influenza activity. However, two important vulnerable groups, children and the elderly, are clearly underrepresented in the GIS. Furthermore, virological confirmation is lacking in the GIS. So, GIS can be a useful addition to the GP system, especially when representativeness can be improved and when participation remains at the current high level.

Influenza-like Illness in Households with Children of Preschool Age

“…Monthly ILI incidence was estimated at 13.2% in parents and 21.6% in children, resulting in an overall rate of 1.72 ILI episodes/parent-year and 2.81 ILI episodes/child-year, respectively. These estimates are higher than those of 7.4-11.8% obtained via an internet-based monitoring system in the Dutch general population during the 2003-2008 winter seasons, 3 suggesting that ILI occurs more often in households with preschool children than in the community. The impact of ILI on the health-care system and on the society as a whole also appears relevant, with 35.7% of children and 17.7% of parents with ILI seeking medical care, and 45.7% and 22.8% of ILI-affected parents and children reporting, respectively, a loss of working and DCC days and about one third of those with ILI taking medications, which often represent out-ofpocket costs.…”

“…It mainly affects preschool children during the winter epidemics. [1][2][3] Besides influenza virus, other viruses and to a lesser extent bacteria can cause ILI. ILI-causing viruses include respiratory syncytial virus, rhinovirus, adenovirus, parainfluenza viruses, human coronaviruses and human metapneumovirus, which are indistinguishable on clinical grounds.…”

Ten-year performance of Influenzanet: ILI time series, risks, vaccine effects, and care-seeking behaviour

“…Based on single-season analysis, previous studies established excellent correlations between ILI incidences as determined by Influenzanet and by ECDC (Friesema et al, 2009;Marquet et al, 2006;van Noort et al, 2007). A question remained on whether this consistency would persist for multiple-season data streams.…”

“…It was initially conceived to make scientific information accessible to a broad public and to kindle students' enthusiasm for science, and was launched in the Netherlands and Belgium (www.degrotegriepmeting.nl) Based on single-season analysis, previous studies established good correlations between ILI incidences as determined by Influenzanet and by the clinical surveillance by sentinel General Practitioners (GPs) as coordinated by the European Centre for Disease Prevention and Control (ECDC) (Friesema et al, 2009;Marquet et al, 2006;van Noort et al, 2007;Paolotti et al, 2014;Vandendijck et al, 2013). The absolute ILI incidence as reported by http Influenzanet is, however, much more consistent across countries according to Influenzanet than reported by the ECDC, due to country specific medical care seeking rates and disparities in ILI case definitions used by GPs in different countries (van Noort et al, 2007).…”

Effectiveness of 2012–2013 influenza vaccine against influenza-like illness in general population

“…[5][6][7] Today, most of these observational studies are based on a population of patients consulting a general practitioner (GP) for ILI, which is not a randomized ILI sample, 8 as the majority of individuals with an ILI do not systematically access the healthcare systems. 9,10 This point highlights the need to provide other IVE estimation methods, not relying on individuals tracked by the healthcare systems.…”