For each contact investigation performed in the period April 29th until June 22nd 2009, the following data were collected: flight arrival date, first day of illness of index patient, date of laboratory diagnosis, date of contact tracing request and the date passenger lists were obtained and contact details were completed ('contacts details identified'). From these data, time intervals (in days) between flight arrival and date of diagnosis (interval I), between diagnosis and request dates (interval II) and between request and contact details identified dates (interval III) were calculated, see Figure 2 . Date of actual contact tracing and oseltamivir administration was not available in this study, but is inherently always hours if not days later. As the airline company traces contacts amongst crewmembers, these are not included in this study.