Indeed, in the current series the number of cases detected in patients over 60 years old is remarkably low: less than 1% in both Panels B and C whilst this age group provided 10.5% of the patients tested in these two panels. This distribution of cases in age groups is of special interest in the light of HI serological results : regardless of the antibody titre considered, it appears clear that the prevalence of antibodies to H1N1sw is low under the age of 30. Since it is extremely improbable that strains related to H1N1sw circulated in human populations during the last 20 or 30 years, the value observed for young patients is likely to be due to cross reactivity with seasonal influenza and thus indicative of the global overestimation of the prevalence provided by the HI assay. In individuals over 40, the prevalence is clearly disconnected from that observed for seasonal viruses and suggests previous exposure to influenza virus antigenically related to the current H1N1sw. However, much earlier circulation of H1N1sw-related strains cannot be ruled out considering the high prevalence values observed for patients over 80. This suggests a ����cause and effect���� relationship, i.e. protection provided by specific antibodies. However, this interpretation should be considered tenuous since the significance of the titres of HI antibodies detected, in terms of protection against infection/ asymptomatic infection/severe forms, is unknown. Moreover, if the group of elderly individuals appears to be collectively prone to a low incidence of H1N1 and H1N1sw infections, individuals without SD-208 immunity to the virus do exist in this age group. Their precise number is unknown since the antibody level that may provide effective protection is undetermined, but the occurrence of a low incidence in this age group does not eliminate during the outbreak the risk of complicated forms and high mortality as classically observed in the case of seasonal influenza infection. Concerning beta-Cyclodextrin diagnosis of the acute infection, it is generally considered that the only reliable tool was the detection of viral genomes using molecular biological methods.