from travel, also efﬁciently restricts the spread of other respiratory illnesses (27). Potential limitations in this study include lack of knowledge of the health status of passengers who did not return the survey or inform health authorities of ILI symptoms after ﬂight arrival, response bias resulting from contact with authorities after ﬂight arrival, recall bias caused by the length of time between ﬂight arrival and survey response; and potential for contracting an ILI postarrival from a source other than the ﬂight. Cross- checking of data collected by local health authorities at the time of ﬂight arrival showed no recall bias. Response levels from passengers contacted by health authorities were higher than those not contacted, thereby limiting response bias. The spectrum of signs and symptoms of passengers contracting ILI or pandemic (H1N1) 2009 varies; therefore, if a passenger did not return the survey or contact medical personnel or health authorities after the ﬂight, some cases may have been missed (28). Media coverage of the arrival of ﬂight 1 requesting passengers with ILI to contact health authorities was substantial. Although many passengers may be assumed to have then sought medical advice, the number of passengers who were not tested but reported ILI symptoms on their survey indicated this assumption was incorrect. Contracting pandemic (H1N1) 2009 postﬂight from a source in the community was unlikely. There was a small chance of contracting the disease preﬂight because of community transmission for ﬂight 1; however, ﬂight 2 originated from an area with no documented community transmission. At the time of investigation, community transmission of pandemic (H1N1) 2009 was not documented at the arrival port. The likelihood of community transmission is also low because all passengers with conﬁrmed pandemic (H1N1) 2009 had symptom onset date within 48 hours after ﬂight arrival. Spread of pandemic (H1N1) 2009 and other ILIs occurred in limited zones of the aircraft during international ﬂights into Australia during May 2009. The time required to contact passengers postﬂight resulted in the potential spread of disease into the community despite guidelines and policies in place to reduce the risk for disease importation. Nonetheless, application of these policies by Australian authorities may have assisted in delaying the importation of identiﬁed pandemic (H1N1) 2009 cases during the ﬁrst month of the recent pandemic. The ﬁndings of this investigation suggest that efforts to prevent importation of respiratory diseases into a community and protection of individuals from in-ﬂight exposure to ILI may require changes in international policies of both exit screening of symptomatic passengers preﬂight and contact tracing of those exposed to an ILI inﬂight. Further research on transmission of ILI in aircraft and into the effects of exit screening at international airport hubs to restrict travel Transmission of Inﬂuenza on International Flights of passengers with symptoms before ﬂying would be of particular interest for respiratory disease of greater severity than pandemic (H1N1) 2009. Acknowledgments We thank the states and territories for provision of data from the NetEpi Database. We also thank Jeremy McAnulty, Paula Spokes, and Kate Ward for critical comment on the manuscript. P.M.K. is funded by Australia’s National Health and Medical Research Council. 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