Among close contacts with symptomatic infection, the median interval between illness onset and sample collection was 0.5 days. More than 85% of close contacts were quarantined within 72 hours after interview of the index case-patients. The median interval between fi rst exposure and quarantine was 3.4 days for the close contacts, and it was shorter, on average, for fl ight passenger contacts than nonpassenger contacts (1.7 days vs. 3.8 days). For symptomatic close contacts infected with pandemic (H1N1) 2009, the median of generation time (i.e., the time from illness onset in an index case to illness onset in a secondary case) were 2.4 days; it was shorter for fl ight passenger contacts than nonpassenger contacts (1.6 days vs. 2.5 days) ( Table 1) .