The spatiotemporal association of non-prescription retail sales with cases during the 2009 influenza pandemic in Great Britain.
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.


METHODS
The UK.


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


METHODS
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.
Department of Clinical Sciences, Liverpool School of Tropical Medicine, Liverpool, UK.
Stacy
S
Todd
Peter J
PJ
Diggle
Peter J
PJ
White
Andrew
A
Fearne
Jonathan M
JM
Read
D000328:Adult; D000998:Antiviral Agents / Q000191:economics*; D003132:Commerce; D006801:Humans; D007251:Influenza, Human / Q000453:epidemiology*; D004366:Nonprescription Drugs / Q000191:economics*; D058873:Pandemics; D013997:Time Factors; D006113:United Kingdom / Q000453:epidemiology
D000998:Antiviral Agents; D004366:Nonprescription Drugs
Influenza; Outbreak; Syndromic Surveillance