The Sentinel Network, a revolution in epidemiology

A formidable French initiative begun under the leadership of Alain-Jacques Valleron, a biomathematician at Inserm, the Sentinel Network ventured into real-time participation, even before the arrival of the Internet. From 1984, it enabled the spread of infectious diseases to be directly monitored through the volunteering efforts of hundreds of general practitioners. A turning point for medical practice and epidemiological research.

© Inserm, P. Latron

Epidemiology through networks, a 21st century version: this is what Alain-Jacques Valleron implemented well ahead of time with the Sentinel Network, even before the arrival of the Internet. Created in 1984, this network has in thirty years become the last word in epidemiological research in France, and allows the general public and physicians to directly witness the spread of some infectious diseases and the appearance of epidemics. "This project was born of my fascination with technology and the need for reliable epidemiological data to feed into models of disease spread," explains the man himself, an expert in the modelling of epidemics.

Obtaining reliable data in real time

From the start of the 1980s, he devoted himself to the development of information systems and statistical or compter models enabling the description, modelling and detection of the dynamics of infections and epidemics in real time. Field data were rare at that time. "There was a system of compulsory reporting for certain illnesses, and reference centres operated by the French General Health Directorate. But the information, submitted by post, was not always sent, or was slow to arrive and be analysed. For measles, for example, the development of the Sentinel Network enabled the observation of failure to report the illness by a factor of a thousand in the 1980s!" illustrates the researcher.

In order to obtain reliable data in real time, he then had the idea of a collaborative network with general practitioners. Having observed the technological advances and the emergence of the first networks between professionals in the United States, even before the arrival of the Internet, he wrote a comprehensive report on the interest of these epidemiological techniques, and sent it to the French General Health Directorate and Inserm’s General Directorate. The green light was then given for the creation of the Sentinel Network, which would come into being a year later. The system enables physicians to log on from their practices to submit information on cases of influenza, mumps, measles, acute diarrhoea, or chickenpox diagnosed in recent days. The initial volunteers took to the system immediately, and a first epidemic of influenza was detected only a few weeks after the tool was launched.

A network coordinated by Inserm researchers and UPMC in collaboration with InVS

Today 1,300 volunteer private general practitioners distributed throughout mainland France belong to the network coordinated by Inserm Joint Research Unit 707, Université Pierre et Marie-Curie, in collaboration with the French Institute for Public Health Surveillance (InVS). Physicians are invited to log on as often as possible, and at least once a week. Data are sent to the server at the Inserm Unit, which checks and interprets the information in the form of summaries, graphs and maps.

The system is flexible, so that new diseases can be easily accommodated, and enables regular, time-limited monitoring. This was the case for asthma attacks between 2002 and 2011, and requests for HIV testing between 1987 and 2002. At the moment, cases of suicide and Lyme disease are being monitored, for example.

Modelling, planning, simulating

This tool generates large databases for several diseases, which can be downloaded free of charge—great for researchers in epidemiology! "Thanks to these databases, it is possible to reconstruct an epidemic by computer, and to test methods of intervention," illustrates Alain-Jacques Valleron. During the H1N1 influenza epidemic, for example, we simulated the impact of closing the schools. That enabled us to know whether this measure would have been useful in stemming the spread of the virus and to predict the number of days for which we would need to close the schools, the number of schools to close, etc. Moreover, since the arrival of the Internet in 1995, the network website offers very easy access to the information collected. This has really marked a turning point for physicians. A general practitioner who observes several cases of influenza-like illnesses in the middle of summer may wonder what it is. It may be an emerging virus, a bioterrorist attack, etc. The ability to check what is happening for his/her colleagues, in the same region and elsewhere, in real time, is highly instructive. Moreover, regular monitoring of the data allows him/her to prepare for an epidemic and to modify his/her practice. Even the wider public has adopted this tool in recent years," he observes.

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