Extension of traditional infectious disease surveillance with a repeated population survey.

Background: Public health surveillance is an important tool for monitoring cases of infectious diseases. Identification of risk factors requires the comparison of exposure between cases and controls. However, standard surveillance systems do not routinely collect information on controls.

Methods: Since 2008, we have extended the surveillance of infectious diseases in The Netherlands with a repeated population survey. This survey is based on the thrice-yearly administration of a questionnaire about potential risk factors for several gastrointestinal, foodborne and respiratory infections to a representative, dynamic sample of the Dutch population. The questionnaire contains questions similar to those used for interviewing cases.

Results: Over 14 mailing rounds, 4926 persons were approached with a response of 36%, with a small underrepresentation of men, young people, people living in large cities and persons with both parents born outside The Netherlands. Costs per completed questionnaire were around 15 euro. Muscle/joint pain in the past 4 weeks was the most reported symptom (44%), followed by running nose (39%) and headache (32%); 5.6% reported gastroenteritis, reflecting an incidence of 997 episodes per 1000 person-years.

Conclusions: Extending traditional surveillance with a repeated population survey offers the unique opportunity to gather data for a multitude of purposes. The survey already has been used in two outbreak investigations and two case-control studies. It is cost-effective and may provide novel epidemiological insights towards risk group and risk factor identification and characterization for a variety of infectious diseases. The survey will be continued and expanded in use.