Comparison of five influenza surveillance systems during the 2009 pandemic and their association with media attention.
BACKGROUND
During the 2009 influenza pandemic period, routine surveillance of influenza-like-illness (ILI) was conducted in The Netherlands by a network of sentinel general practitioners (GPs). In addition during the pandemic period, four other ILI/influenza surveillance systems existed. For pandemic preparedness, we evaluated the performance of the sentinel system and the others to assess which of the four could be useful additions in the future. We also assessed whether performance of the five systems was influenced by media reports during the pandemic period.


METHODS
The trends in ILI consultation rates reported by sentinel GPs from 20 April 2009 through 3 January 2010 were compared with trends in data from the other systems: ILI cases self-reported through the web-based Great Influenza Survey (GIS); influenza-related web searches through Google Flu Trends (GFT); patients admitted to hospital with laboratory-confirmed pandemic influenza, and detections of influenza virus by laboratories. In addition, correlations were determined between ILI consultation rates of the sentinel GPs and data from the four other systems. We also compared the trends of the five surveillance systems with trends in pandemic-related newspaper and television coverage and determined correlation coefficients with and without time lags.


RESULTS
The four other systems showed similar trends and had strong correlations with the ILI consultation rates reported by sentinel GPs. The number of influenza virus detections was the only system to register a summer peak. Increases in the number of newspaper articles and television broadcasts did not precede increases in activity among the five surveillance systems.


CONCLUSIONS
The sentinel general practice network should remain the basis of influenza surveillance, as it integrates epidemiological and virological information and was able to maintain stability and continuity under pandemic pressure. Hospital and virological data are important during a pandemic, tracking the severity, molecular and phenotypic characterization of the viruses and confirming whether ILI incidence is truly related to influenza virus infections. GIS showed that web-based, self-reported ILI can be a useful addition, especially if virological self-sampling is added and an epidemic threshold could be determined. GFT showed negligible added value.
National Institute for Public Health and the Environment (RIVM), Centre for Infectious Disease Control Netherlands, P,O, Box 1, 3720 BA Bilthoven, The Netherlands. marit.de.lange@rivm.nl.
Marit M A
MM
de Lange
Adam
A
Meijer
Ingrid H M
IH
Friesema
Gé A
GA
Donker
Carl E
CE
Koppeschaar
Mariëtte
M
Hooiveld
Nel
N
Ruigrok
Wim
W
van der Hoek
D000293:Adolescent; D000328:Adult; D000368:Aged; D002648:Child; D002675:Child, Preschool; D005260:Female; D006801:Humans; D007223:Infant; D007231:Infant, Newborn; D053118:Influenza A Virus, H1N1 Subtype / Q000302:isolation & purification; D007251:Influenza, Human / Q000453:epidemiology* / Q000517:prevention & control; D008297:Male; D008402:Mass Media; D008875:Middle Aged; D009426:Netherlands / Q000453:epidemiology; D009524:Newspapers as Topic; D058873:Pandemics / Q000517:prevention & control*; D015397:Program Evaluation; D012621:Seasons; D018571:Sentinel Surveillance; D013690:Television