Article Text

The spatiotemporal association of non-prescription retail sales with cases during the 2009 influenza pandemic in Great Britain
  1. Stacy Todd1,2,
  2. Peter J Diggle3,4,
  3. Peter J White5,6,7,
  4. Andrew Fearne8,
  5. Jonathan M Read3
  1. 1Department of Clinical Sciences, Liverpool School of Tropical Medicine, Liverpool, UK
  2. 2Oxford University Clinical Research Unit, Wellcome Trust Major Overseas Programme, Ho Chi Minh City, Vietnam
  3. 3Institute of Infection and Global Health, University of Liverpool, Liverpool, UK
  4. 4Lancaster Medical School, University of Lancaster, Lancaster, UK
  5. 5Department of Infectious Disease Epidemiology, MRC Centre for Outbreak Analysis and Modelling, Imperial College School of Public Health, London, UK
  6. 6NIHR Health Protection Research Unit in Modelling Methodology, Department of Infectious Disease Epidemiology, Imperial College School of Public Health, London, UK
  7. 7Modelling and Economics Unit, Centre for Infectious Disease Surveillance and Control, Public Health England, London, UK
  8. 8Kent Business School, University of Kent, Canterbury, UK
  1. Correspondence to Dr Jonathan M Read; jonread{at}


Objective To assess whether retail sales of non-prescription products can be used for syndromic surveillance and whether it can detect influenza activity at different spatial scales. A secondary objective was to assess whether changes in purchasing behaviour were related to public health advice or levels of media or public interest.

Setting The UK.

Participants National and regional influenza case estimates and retail sales from a major British supermarket.

Outcome measures Weekly, seasonally adjusted sales of over-the-counter symptom remedies and non-pharmaceutical products; recommended as part of the advice offered by public health agencies; were compared with weekly influenza case estimates. Comparisons were made at national and regional spatial resolutions. We also compared sales to national measures of contemporaneous media output and public interest (Internet search volume) related to the pandemic.

Results At a national scale there was no significant correlation between retail sales of symptom remedies and cases for the whole pandemic period in 2009. At the regional scale, a minority of regions showed statistically significant positive correlations between cases and sales of adult ‘cold and flu’ remedies and cough remedies (3.2%, 5/156, 3.8%, 6/156), but a greater number of regions showed a significant positive correlation between cases and symptomatic remedies for children (35.6%, 55/156). Significant positive correlations between cases and sales of thermometers and antiviral hand gels/wash were seen at both spatial scales (Cor 0.477 (95% CI 0.171 to 0.699); 0.711 (95% CI 0.495 to 0.844)). We found no significant association between retail sales and media reporting or Internet search volume.

Conclusions This study provides evidence that the British public responded appropriately to health messaging about hygiene. Non-prescription retail sales at a national level are not useful for the detection of cases. However, at finer spatial scales, in particular age-groups, retail sales may help augment existing surveillance and merit further study.

  • Influenza
  • Syndromic Surveillance
  • Outbreak

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