It is not surprising that there was a close relationship between the clinical and virological sentinel data. This relationship should be close, because the diagnosis of ILI or ARI and the subsequent collection of respiratory specimens is done by the same person (sentinel GP). Sampling of specimens is also usually at its highest during the period of increased influenza activity, which will lead to increased numbers of positive specimens. Some of the non-matches of sentinel data occurred during the Christmas/New Year period when the clinical and virological surveillance systems are affected by holidays.