Protecting your home and community

Influenzanet: Real Time Surveillance of Influenza Prevalence in Europe


A photo of Camp Funkston in Kansas during the 1918 flu pandemicInfluenzanet is a real-time surveillance system that monitors the prevalence of influenza-like-illness (ILI) with the aid of volunteers via the Internet. Residents of the participating countries register online, and weekly during during the flu season, participants are asked to report symptoms they have experienced.

Belgium and The Netherlands launched the program during the 2003/2004 flu season:  since then, Denmark, France, Ireland, Italy, Portugal, Spain, Sweden, and the United Kingdom have become partners.

An image of flu prevalence in the UK on 2014-01-28 at 16:38

ILI prevalence in the UK is updated every three minutes

The method used by the partner countries is designed to reduce the bias inherent in the population that volunteers to be reporters. For example, since people with flu-like symptoms (influenza-like illness, or ILI) are most likely to sign up, the first symptoms questionnaire from each volunteer is ignored. The U.K. version of the intake questionnaire can be found here.

A photo of a young man with the flu

Photo credit Jess and Colin Liotta



A case of ILI is defined based on a the sudden onset of reported symptoms and at least one of the four systemic symptoms:

  • Fever and/or chills
  • Feeling tired or exhausted
  • Headache
  • Muscle pain

And at least one of the three respiratory symptoms:

  • Cough
  • Sore throat
  • Shortness of breath (dyspnoea)

An image of the results page from InfluenzanetThe ability to see ILI activity is startling. The interactive results page allows the visitor to compare and follow flu activity among all the partner countries.

At a glance the visitor can tell that all is very much not well in Italy and Sweden, while ILI activity in Belgium and the Netherlands is somewhat quiescent.

Incidence of ILI in France appears to be on the wane, as in Spain, while it looks like the UK is beginning to spike. Portugal might be beginning to spike, or maybe if we check back later we’ll find out that it’s actually plateaued.

How does Influenzanet compare with traditional, MD-based surveillance systems?

A study of five surveillance systems in place during the 2009 influenza pandemic, including Influenzanet, found strong correlations among the results. Authors Marit MA de Lange, Adam Meijer, et al., found that there was no correlation between peak numbers of cases during the summer of 2009 and the incidence of television broadcasts and articles in print media. Their results suggest that systems that collect data on self-reported ILI, such as Influenzanet, can be a useful tool in real-time flu surveillance.

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