However, it was also noticed that attack rates in children increased with age sub-Cyclohexaamylose groups, the risk of infection among teenagers being 3 times the risk of the youngest. This difference may be, in the case of the current investigation, explained in part by the physical separation of children in different groups, but may also MCB-613 reflect specific behaviour or susceptibility to infection in different age groups. Finally, the genetic characterisation of a strain isolated in the early period of the outbreak from a patient returning from Mexico, and that of a strain isolated in July 2009 from a French autochthonous case revealed two mutations at positions 106 and 248 of the neuraminidase protein. Residue 106 is located at the N terminus of the neuraminidase domain and closely related to the trans-membrane domain. Residue 248 is located at the surface of the protein and part of an antibody recognition site. It may therefore be associated with antigenic shift. The N248D mutation has previously been reported in H1N1 human strains isolated in the thirties, forties, seventies, eighties and nineties. Sequence analysis suggests that a majority of strains harboured the V106N248 pattern at the origin of the outbreak. The mechanism of emergence of ID strains remains unclear: such strains may have emerged from a common ancestor and disseminated secondarily, but this hypothesis is epidemiologically puzzling and poorly supported by phylogenetic analyses in other genes such as HA. The alternative hypothesis cannot be ruled out and would suggest that evolutionary constraints led to the decline of V106-N248 strains after May 2009 and the emergence of I106-D248. To our knowledge, this phenomenon has not been associated to date with a change in the epidemiology or clinical presentation of the viral infection, but certainly deserves a careful follow up during the coming months. Hemoglobin and myoglobin are the two major respiratory hemoproteins burdened with the task of maintaining aerobic life: Hb shuttles oxygen from the lungs to tissues, while Mb maintains a store of oxygen in muscles, ready for use.