Letter reporting the use of a validated method of identifying periods of high disease activity to describe the seasonal pattern of seasonal allergic rhinoconjunctivitis (SAR) in the United Kingdom.  The Google trends application (Google, Mountain View, CA, USA) was searched for the terms 'hay fever' and 'hayfever', limited to the United Kingdom and the months of Jan 2008 to Dec 2010.  The combined results demonstrated a consistent pattern of online search engine activity.  No search activity is seen during Winter.  Searches begin in Spring, with a small peak in the search volume index in late Apr/early May and a larger peak in mid-June.  The smaller peak occurs during the peak tree pollen season (e.g. birch), while the larger peak occurs during the peak grass pollen season.

The writers suggest that this inadvertent mass collaboration provides useful information as to the timing of peak symptoms of allergic rhinoconjunctivitis in the United Kingdom.